What's smaller than a Feather but larger than a Trinket? It's an Adafruit ItsyBitsy nRF52840 Express featuring the Nordic nRF52840 Bluetooth LE processor! Teensy & powerful, with an fast nRF52840 Cortex M4 processor running at 64 MHz and 1 MB of FLASH - this microcontroller board is perfect when you want something very compact, with a heap-load of memory and Bluetooth LE support This Itsy is your best option for tiny wireless connectivity - it can act as both a BLE central and peripheral, with support in both Arduino and CircuitPython.

ItsyBitsy nRF52840 Express is only 1.4" long by 0.7" wide, but has 6 power pins, 21 digital GPIO pins (6 of which can be analog in). It's the same chip as the Feather nRF52840 but really really small. So it's great for those really compact builds. It even comes with 2MB of QSPI Flash built in, for data logging, file storage, or CircuitPython code.

The most exciting part of the ItsyBitsy is that while we ship it with an Arduino IDE compatible demo, you can also install CircuitPython on board with only a few clicks. When you plug it in, it will show up as a very small disk drive with code.py on it. Edit code.py with your favorite text editor to build your wireless-enabled project using Python, the most popular programming language. No installs, IDE or compiler needed, so you can use it on any computer, even ChromeBooks or computers you can't install software on. When you're done, unplug the Itsy and your code will go with you.

Here are some of the updates you can look forward to when using ItsyBitsy nRF52:

  • Same size, form-factor as the remaining ItsyBitsy mainboards - with a similar but not identical pinout (there's no pins at the end of the board like most other Itsy's due to the radio antenna being there.
  • Floating point support with Cortex M4 DSP instructions
  • 32-bit, 3.3V logic and power with power/enable pin
  • 1024 KB flash, 256 KB RAM
  • 2 MB QSPI FLASH chip for storing files and CircuitPython code storage.
  • Native Open Source USB stack - pre-programmed with UF2 bootloader
  • Bluetooth Low Energy compatible 2.4GHz radio (Details available in the nRF52840 product specification)
  • FCC / IC / TELEC certified module
  • Up to +8dBm output power
  • 21 GPIO, 6 x 12-bit ADC pins, up to 12 PWM outputs (3 PWM modules with 4 outputs each)
  • Blue LED for general purpose blinking, mini DotStar RGB LED for colorful feedback
  • 1 x Special Vhigh output pin gives you the higher voltage from VBAT or VUSB, for driving NeoPixels, servos, and other 5V-logic devices. Digital 5 level-shifted output for high-voltage logic level output.
  • Native USB supported by every OS - can be used in Arduino or CircuitPython as USB serial console, Keyboard/Mouse HID, even a little disk drive for storing Python scripts.
  • Can be used with Arduino IDE or CircuitPython
  • Comes pre-loaded with the UF2 bootloader, which looks like a USB storage key. Simply drag firmware on to program, no special tools or drivers needed! It can be used to load up CircuitPython or Arduino IDE

Each order comes with one assembled and tested ItsyBitsy nRF52840, with headers that can be soldered in for use with a breadboard.

So what are you waiting for? Pick up a ItsyBitsy nRF today and be amazed at how easy and fast it is to get started with the teensiest Bluetooth dev board we have.

Power Pins

The ItsyBitsy nRF52840 Express has BAT G USB on the top left, next to the micro USB port

These pins are:

  • BAT - battery input for an alternative power source to USB, the voltage can only be from 3.5V to 6VDC
  • GND - Power/data ground
  • USB - This is the same pin as the MicroUSB connector's 5V USB power pin. This should be used as an output to get 5V power from the USB port. Say if you need to power a bunch of NeoPixels or servos.

You can always put any voltage you like into BAT and the circuitry will switch between BAT and USB dynamically for you. That means you can have a Battery backup that only gets enabled when USB is disconnected.

If you want to add rechargeable power, a LiPoly backpack can be soldered into these three pins that will let you have a battery that is automatically recharged whenever USB is plugged in, then switches to LiPoly when on the go:

Adafruit LiIon/LiPoly Backpack Add-On for Pro Trinket/ItsyBitsy

PRODUCT ID: 2124
If you have an ItsyBitsy or Pro Trinket you probably know it's the perfect little size for a portable project. This LiPoly backpack makes it really easy to do! Instead of wiring 2...
$4.95
IN STOCK

In addition to the three standard power pins, the ItsyBitsy nRF52840 Express has a few more pins available for power sourcing:

  • 3V - this is the regulated output from the onboard regulator. You can draw 500mA whether powered by USB or battery.
  • EN - connected to the regulator enable, it will let you shut off power - when running on battery only. But at least you don't have to cut a trace or wire to your battery. This pin does not affect power when using USB
  • Vhi - this is a special pin! It is a dual-Schottky-diode connected output from BAT and USB. This means this will always have the higher-of-the-two voltages, but will always have power output. The voltage will be about 5VDC when powered by USB, but can range from 3.5-6VDC when powered from battery. It's not regulated, but it is high-current, great for driving servos and NeoPixels.

Analog Inputs

The 7 available analog inputs (A0 .. A5 and D10 which is called A6) can be configured to generate 8, 10 or 12-bit data (or 14-bits with over-sampling), at speeds up to 200kHz (depending on the bit-width of the values generated), based on an internal 0.6V reference

The following default values are used:

  • Default voltage range: 0-3.6V (uses the internal 0.6V reference with 1/6 gain)
  • Default resolution: 12-bit (0..4096)
  • Default mV per lsb (assuming 3.6V and 12-bit resolution): 1 LSB = 0.87890625 mV

Since the AREF can be scaled internally, we don't have an external AREF pin - it's not needed!

Unlike digital functions, which can be remapped to any GPIO/digital pin, the ADC functionality is tied to specified pins, A0 thru A5 and also D10/A6

PWM Outputs

Any GPIO pin can be configured as a PWM output, using the dedicated PWM block.

Three PWM modules can provide up to 12 PWM channels with individual frequency control in groups of up to four channels.

I2C Pins

I2C pins on the nRF52840 require external pullup resistors to function, which are not present on the Adafruit nRF52840 Feather by default. You will need to supply external pullups to use these. All Adafruit I2C breakouts have appropriate pullups on them already, so this normally won't be an issue for you.

Logic pins

This is the general purpose I/O pin set for the microcontroller. All logic except for pin 5 is 3.3V output and input. You can usually use 3V logic as an input to 5V, but the 3V Itsy pins should not be connected to 5V!

All pins can do PWM output  - nRF52840 will assign a PWM to any pin you like
All pins can be interrupt inputs  - nRF52840 will assign an IRQ to any pin you like

D2 and A1 thru A5 are 'low speed' pins, they can be used for < 10KHz signals but not recommended for higher frequencies so as to avoid radio interference. Any other pins will work at high speeds!

Special GPIO

Since you have PWM/IRQ on any pin, there's not a lot of special pins - they can all pretty much do anything, like connect a PDM microphone or encoder. Here are the somewhat special pins:

  • #0 / RX - GPIO #0, also receive (input) pin for Serial1
  • #1 / TX - GPIO #1, also transmit (output) pin for Serial1
  • SDA and SCL - these are the I2C hardware interface pins. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup on each to 3.3V. PWM output
  • #3 - GPIO #3 is connected to the blue LED next to the Reset button - it isn't available on the pin breakouts
  • #4 - GPIO #4 is connected to the SW button to the right of the micro USB connector - it isn't available on the pin breakouts
  • #5 - GPIO #5. This is a special OUTPUT-only pin that can PWM. It is level-shifted up to Vhi voltage, so it's perfect for driving NeoPixels that want a ~5V logic level input. You can use this with our NeoPixel DMA control library to automatically write NeoPixel data without needing any processor time.
  • SCK/MOSI/MISO - the hardware SPI port for connecting SPI devices, you can use any pin for CS

These pins are available in CircuitPython under the board module. Names that start with # are prefixed with D and other names are as is. So #0 / RX above is available as board.D0 and board.RX for example.

QSPI Flash and DotStar

As part of the 'Express' series of boards, this ItsyBitsy is designed for use with CircuitPython.

To make that easy, we have added two extra parts: a mini DotStar (RGB LED) and a 2 MB QSPI (Quad SPI) Flash chip.

The DotStar is connected to pin #6 (clock) and #8 (data) in Arduino, so just use our DotStar library and set it up as a single-LED strand on pins 6 & 8. The DotStar is powered by the 3.3V power supply but that hasn't shown to make a big difference in brightness or color.

The QSPI Flash is connected to 6 pins that are not brought out on the GPIO pads. QSPI is neat because it allows you to have 4 data in/out lines instead of just SPI's single line in and single line out. This means that QSPI is at least 4 times faster. But in reality is at least 10x faster because you can clock the QSPI peripheral much faster than a plain SPI peripheral

We have an Arduino library here which provides QSPI interfacing for Arduino. In CircuitPython, the QSPI flash is used natively by the interpreter and is read-only to user code, instead the Flash just shows up as the writable disk drive!

Other Pins

A tactile switch is provided for use in your projects, which is connected to P0.29 and is accessible in code as D4.

Holding this button down coming out of a board reset will also force the device to enter and remain in USB bootloader mode, which can be useful if you lock your board up with bad application code!

RST - this is the Reset pin, tie to ground to manually reset the nRF52840, as well as launch the bootloader manually

SWCLK & SWDIO - These are the debug-interface pins, used if you want to reprogram the chip directly or attach a debugger.

You can install the Adafruit Bluefruit nRF52 BSP (Board Support Package) in two steps:

nRF52 support requires at least Arduino IDE version 1.8.6! Please make sure you have an up to date version before proceeding with this guide!
Please consult the FAQ section at the bottom of this page if you run into any problems installing or using this BSP!

1. BSP Installation

Recommended: Installing the BSP via the Board Manager

  • Download and install the Arduino IDE (At least v1.8)
  • Start the Arduino IDE
  • Go into Preferences
  • Add https://www.adafruit.com/package_adafruit_index.json as an 'Additional Board Manager URL' (see image below)
  • Restart the Arduino IDE
  • Open the Boards Manager option from the Tools -> Board menu and install 'Adafruit nRF52 by Adafruit' (see image below)

It will take up to a few minutes to finish installing the cross-compiling toolchain and tools associated with this BSP.

The delay during the installation stage shown in the image below is normal, please be patient and let the installation terminate normally:

Once the BSP is installed, select

  • Adafruit Bluefruit nRF52832 Feather (for the nRF52 Feather)
  • Adafruit Bluefruit nRF52840 Feather Express (for the nRF52840 Feather)
  • Adafruit ItsyBitsy nRF52840 (for the Itsy '850)
  • Adafruit Circuit Playground Bluefruit (for the CPB)
  • etc...

from the Tools -> Board menu, which will update your system config to use the right compiler and settings for the nRF52:

2. LINUX ONLY: adafruit-nrfutil Tool Installation

adafruit-nrfutil is a modified version of Nordic's nrfutil, which is used to flash boards using the built in serial bootloader. It is originally written for python2, but have been migrated to python3 and renamed to adafruit-nrfutil since BSP version 0.8.5.

This step is only required on Linux, pre-built binaries of adafruit-nrfutil for Windows and MacOS are already included in the BSP. That should work out of the box for most setups.

Install python3 if it is not installed in your system already

Download: file
$ sudo apt-get install python3

Then run the following command to install the tool from PyPi

Download: file
$ pip3 install --user adafruit-nrfutil

Add pip3 installation dir to your PATH if it is not added already. Make sure adafruit-nrfutil can be executed in terminal by running

Download: file
$ adafruit-nrfutil version
adafruit-nrfutil version 0.5.3.post12

3. Update the bootloader (nRF52832 ONLY)

To keep up with Nordic's SoftDevice advances, you will likely need to update your bootloader if you are using the original nRF52832 based Bluefruit nRF52 Feather boards.

Follow this link for instructions on how to do that

This step ISN'T required for the newer nRF52840 Feather Express, which has a different bootloader entirely!

Advanced Option: Manually Install the BSP via 'git'

If you wish to do any development against the core codebase (generate pull requests, etc.), you can also optionally install the Adafruit nRF52 BSP manually using 'git', as decribed below:

Adafruit nRF52 BSP via git (for core development and PRs only)

  1. Install BSP via Board Manager as above to install compiler & tools.
  2. Delete the core folder nrf52 installed by Board Manager in Adruino15, depending on your OS. It could be
    macOS~/Library/Arduino15/packages/adafruit/hardware/nrf52
    Linux~/.arduino15/packages/adafruit/hardware/nrf52
    Windows%APPDATA%\Local\Arduino15\packages\adafruit\hardware\nrf52
  3. Go to the sketchbook folder on your command line, which should be one of the following:
    macOS: ~/Documents/Arduino
    Linux: ~/Arduino
    Windows: ~/Documents/Arduino
  4. Create a folder named hardware/Adafruit, if it does not exist, and change directories into it.
  5. Clone the Adafruit_nRF52_Arduino repo in the folder described in step 2:
    git clone --recurse-submodules [email protected]:adafruit/Adafruit_nRF52_Arduino.git
  6. This should result in a final folder name like ~/Documents/Arduino/hardware/Adafruit/Adafruit_nRF52_Arduino (macOS).

  7. Restart the Arduino IDE

The nRF52 family includes an adjustable 'successive-approximation ADC' which can be configured to convert data with up to 14-bit resolution (0..16383), and the reference voltage can be adjusted up to 3.6V internally.

The default values for the ADC are 10-bit resolution (0..1023) with a 3.6V reference voltage, meaning every digit returned from the ADC = 3600mV/1024 = 3.515625mV.

Analog Reference Voltage

The internal reference voltage is 0.6V with a variable gain setting, and can be adjust via the analogReference(...) function, providing one of the following values:

  • AR_INTERNAL (0.6V Ref * 6 = 0..3.6V) <-- DEFAULT
  • AR_INTERNAL_3_0 (0.6V Ref * 5 = 0..3.0V)
  • AR_INTERNAL_2_4 (0.6V Ref * 4 = 0..2.4V)
  • AR_INTERNAL_1_8 (0.6V Ref * 3 = 0..1.8V)
  • AR_INTERNAL_1_2 (0.6V Ref * 2 = 0..1.6V)
  • AR_VDD4 (VDD/4 REF * 4 = 0..VDD)

For example:

Download: file
// Set the analog reference to 3.0V (default = 3.6V)
analogReference(AR_INTERNAL_3_0);

Analog Resolution

The ADC resolution can be set to 8, 10, 12 or 14 bits using the analogReadResolution(...) function, with the default value being 10-bit:

Download: file
// Set the resolution to 12-bit (0..4095)
analogReadResolution(12); // Can be 8, 10, 12 or 14

Default ADC Example (10-bit, 3.6V Reference)

The original source for this code is included in the nRF52 BSP and can be viewed online here.

int adcin    = A5;
int adcvalue = 0;
float mv_per_lsb = 3600.0F/1024.0F; // 10-bit ADC with 3.6V input range

void setup() {
  Serial.begin(115200);
  while ( !Serial ) delay(10);   // for nrf52840 with native usb
}

void loop() {
  // Get a fresh ADC value
  adcvalue = analogRead(adcin);

  // Display the results
  Serial.print(adcvalue);
  Serial.print(" [");
  Serial.print((float)adcvalue * mv_per_lsb);
  Serial.println(" mV]");

  delay(100);
}

Advanced Example (12-bit, 3.0V Reference)

The original source for this code is included in the nRF52 BSP and can be viewed online here.

#include <Arduino.h>

#if defined ARDUINO_NRF52840_CIRCUITPLAY
#define  PIN_VBAT          A8   // this is just a mock read, we'll use the light sensor, so we can run the test
#endif

uint32_t vbat_pin = PIN_VBAT;             // A7 for feather nRF52832, A6 for nRF52840

#define VBAT_MV_PER_LSB   (0.73242188F)   // 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096

#ifdef NRF52840_XXAA
#define VBAT_DIVIDER      (0.5F)          // 150K + 150K voltage divider on VBAT
#define VBAT_DIVIDER_COMP (2.0F)          // Compensation factor for the VBAT divider
#else
#define VBAT_DIVIDER      (0.71275837F)   // 2M + 0.806M voltage divider on VBAT = (2M / (0.806M + 2M))
#define VBAT_DIVIDER_COMP (1.403F)        // Compensation factor for the VBAT divider
#endif

#define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)


float readVBAT(void) {
  float raw;

  // Set the analog reference to 3.0V (default = 3.6V)
  analogReference(AR_INTERNAL_3_0);

  // Set the resolution to 12-bit (0..4095)
  analogReadResolution(12); // Can be 8, 10, 12 or 14

  // Let the ADC settle
  delay(1);

  // Get the raw 12-bit, 0..3000mV ADC value
  raw = analogRead(vbat_pin);

  // Set the ADC back to the default settings
  analogReference(AR_DEFAULT);
  analogReadResolution(10);

  // Convert the raw value to compensated mv, taking the resistor-
  // divider into account (providing the actual LIPO voltage)
  // ADC range is 0..3000mV and resolution is 12-bit (0..4095)
  return raw * REAL_VBAT_MV_PER_LSB;
}

uint8_t mvToPercent(float mvolts) {
  if(mvolts<3300)
    return 0;

  if(mvolts <3600) {
    mvolts -= 3300;
    return mvolts/30;
  }

  mvolts -= 3600;
  return 10 + (mvolts * 0.15F );  // thats mvolts /6.66666666
}

void setup() {
  Serial.begin(115200);
  while ( !Serial ) delay(10);   // for nrf52840 with native usb

  // Get a single ADC sample and throw it away
  readVBAT();
}

void loop() {
  // Get a raw ADC reading
  float vbat_mv = readVBAT();

  // Convert from raw mv to percentage (based on LIPO chemistry)
  uint8_t vbat_per = mvToPercent(vbat_mv);

  // Display the results

  Serial.print("LIPO = ");
  Serial.print(vbat_mv);
  Serial.print(" mV (");
  Serial.print(vbat_per);
  Serial.println("%)");

  delay(1000);
}

NOTE: For FAQs relating to the BSP, see the dedicated BSP FAQ list.

What are the differences between the nRF51 and nRF52 Bluefruit boards? Which one should I be using?

The two board families take very different design approaches.

All of the nRF51 based modules are based on an AT command set (over UART or SPI), and require two MCUs to run: the nRF51 hosting the AT command parser, and an external MCU sending AT style commands.

The nRF52 boards run code directly on the nRF52, executing natively and calling the Nordic S132 SoftDevice (their proprietary Bluetooth Low Energy stack) directly. This allows for more efficient code since there is no intermediate AT layer or transport, and also allows for lower overall power consumption since only a single device is involved.

The nRF52 will generally give you better performance, but for situation where you need to use an MCU with a feature the nRF52 doesn't have (such as USB), the nRF51 based boards will still be the preferable solution.

Can I run nRF51 Bluefruit sketches on the nRF52?

No. The two board families are fundamentally different, and have entirely separate APIs and programming models. If you are migrating from the nRF51 to the nRF52, you will need to redesign your sketches to use the newer API, enabling you to build code that runs natively on the nRF52832 MCU.

Can I use the nRF52 as a Central to connect to other BLE peripherals?

The S132 Soft Device and the nRF52832 HW support Central mode, so yes this is possible. At this early development stage, though, there is only bare bones support for Central mode in the Adafruit nRF52 codebase, simply to test the HW and S132 and make sure that everything is configured properly. An example is provided of listening for incoming advertising packets, printing the packet contents and meta-data out to the Serial Monitor. We hope to add further Central mode examples in the future, but priority has been given to the Peripheral API and examples for the initial release.

How are Arduino sketches executed on the nRF52? Can I do hard real time processing (bit-banging NeoPixels, Software Serial etc.)?

In order to run Arduino code on the nRF52 at the same time as the low level Bluetooth Low Energy stack, the Bluefruit nRF52 Feather uses FreeRTOS as a task scheduler. The scheduler will automatically switch between tasks, assigning clock cycles to the highest priority task at a given moment. This process is generally transparent to you, although it can have implications if you have hard real time requirements. There is no guarantee on the nRF52 to meet hard timing requirements when the radio is enabled an being actively used for Bluetooth Low Energy. This isn't possible on the nRF52 even without FreeRTOS, though, since the SoftDevice (Nordic's propietary binary blob stack) has higher priority than any user code, including control over interrupt handlers.

Can I use GDB to debug my nRF52?

You can, yes, but it will require a Segger J-Link (that's what we've tested against anyway, other options exist), and it's an advanced operation. But if you're asking about it, you probably know that.

Assuming you have the Segger J-Link drivers installed, you can start Segger's GDB Server from the command line as follows (OSX/Linux used here):

$ JLinkGDBServer -device nrf52832_xxaa -if swd -speed auto

Then open a new terminal window, making sure that you have access to gcc-arm-none-eabi-gdb from the command line, and enter the following command:

$ ./arm-none-eabi-gdb something.ino.elf

`something.ino.elf` is the name of the .elf file generated when you built your sketch. You can find this by enabling 'Show verbose output during: [x] compilation' in the Arduino IDE preferences. You CAN run GDB without the .elf file, but pointing to the .elf file will give you all of the meta data like displaying the actual source code at a specific address, etc.

Once you have the (gdb) prompt, enter the following command to connect to the Segger GDB server (updating your IP address accordingly, since the HW isn't necessarily local!):

(gdb) target remote 127.0.0.1:2331

If everything went well, you should see the current line of code where the device is halted (normally execution on the nRF52 will halt as soon as you start the Segger GDB Server).

At this point, you can send GDB debug commands, which is a tutorial in itself! As a crash course, though:

  • To continue execution, type 'monitor go' then 'continue'
  • To stop execution (to read register values, for example.), type 'monitor halt'
  • To display the current stack trace (when halted) enter 'bt'
  • To get information on the current stack frame (normally the currently executing function), try these:
    • info frame: Display info on the current stack frame
    • info args: Display info on the arguments passed into the stack frame
    • info locals: Display local variables in the stack frame
    • info registers: Dump the core ARM register values, which can be useful for debugging specific fault conditions

Are there any other cross platform or free debugging options other than GDB?

If you have a Segger J-Link, you can also use Segger's OZone debugger GUI to interact with the device, though check the license terms since there are usage restrictions depending on the J-Link module you have.

You will need to connect your nRF52 to the J-Link via the SWD and SWCLK pins on the bottom of the PCB, or if you are OK with fine pitch soldering via the SWD header.

You can either solder on a standard 2x5 SWD header on the pad available in the board, or you can solder wires to the SWD and SWCLK pads on the bottom of the PCB and use an SWD Cable Breakout Board, or just connect cables directly to your J-Link via some other means.

You will also need to connect the VTRef pin on the JLink to 3.3V on the Feather to let the J-Link know what voltage level the target has, and share a common GND by connecting the GND pins on each device. 

Before you can start to debug, you will need to get the .elf file that contains all the debug info for your sketch. You can find this file by enabling Show Verbose Output During: compilation in the Arduino Preferences dialogue box. When you build your sketch, you need to look at the log output, and find the .elf file, which will resemble something like this (it will vary depending on the OS used): /var/folders/86/hb2vp14n5_5_yvdz_z8w9x_c0000gn/T/arduino_build_118496/ancs_oled.ino.elf

In the OZone New Project Wizard, when prompted to select a target device in OZone select nRF52832_xxAA, then make sure that you have set the Target Interface for the debugger to SWD, and finally point to the .elf file above:

Next select the Attach to running program option in the top-left hand corner, or via the menu system, which will cause the debugger to connect to the nRF52 over SWD:

At this point, you can click the PAUSE icon to stop program execution, and then analyze variables, or set breakpoints at appropriate locations in your program execution, and debug as you would with most other embedded IDEs!

Clicking on the left-hand side of the text editor will set a breakpoint on line 69 in the image below, for example, and the selecting Debug > Reset > Reset & Run from the menu or icon will cause the board to reset, and you should stop at the breakpoint you set:

You can experiment with adding some of the other debug windows and options via the View menu item, such as the Call Stack which will show you all of the functions that were called before arriving at the current breakpoint:

Can I make two Bluefruit nRF52's talk to each other?

Yes, by running one board in peripheral mode and one board in central mode, where the central will establish a connection with the peripheral board and you can communicate using BLE UART or a custom service.  See the following Central BLE UART example to help you get started: https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/libraries/Bluefruit52Lib/examples/Central

On Linux I'm getting 'arm-none-eabi-g++: no such file or directory', even though 'arm-none-eabi-g++' exists in the path specified. What should I do?

This is probably caused by a conflict between 32-bit and 64-bit versions of the compiler, libc and the IDE. The compiler uses 32-bit binaries, so you also need to have a 32-bit version of libc installed on your system (details). Try running the following commands from the command line to resolve this:

sudo dpkg --add-architecture i386
sudo apt-get update
sudo apt-get install libc6:i386

what should I do when Arduino failed to upload sketch to my Feather ?

If you get this error:

Timed out waiting for acknowledgement from device.

Failed to upgrade target. Error is: No data received on serial port. Not able to proceed.
Traceback (most recent call last):
  File "nordicsemi\__main__.py", line 294, in serial
  File "nordicsemi\dfu\dfu.py", line 235, in dfu_send_images
  File "nordicsemi\dfu\dfu.py", line 203, in _dfu_send_image
  File "nordicsemi\dfu\dfu_transport_serial.py", line 155, in send_init_packet
  File "nordicsemi\dfu\dfu_transport_serial.py", line 243, in send_packet
  File "nordicsemi\dfu\dfu_transport_serial.py", line 282, in get_ack_nr
nordicsemi.exceptions.NordicSemiException: No data received on serial port. Not able to proceed.

This is probably caused by the bootloader version mismatched on your feather and installed BSP. Due to the difference in flash layout (more details) and Softdevice API (which is bundled with bootloader), sketch built with selected bootloader can only upload to board having the same version. In short, you need to upgrade/burn bootloader to match on your Feather, follow above Update The Bootloader guide

It only has to be done once to update your Feather

Do Feather/Metro nRF52832 and nRF52840 support BLE Mesh ?

They all support BLE Mesh, but we don't provide Arduino library for Mesh. You need to write code based on Nordic sdk mesh. 

Unable to upload sketch/update bootloader with macOS

If you get error similar to this:

Arduino: 1.8.8 (Mac OS X), Board: "Adafruit Bluefruit nRF52832 Feather, 0.2.9 (s132 6.1.1), Level 0 (Release)"

[1716] Error loading Python lib '/var/folders/gw/b0cg4zm508qf_rf2m655gd3m0000gn/T/_MEIE6ec69/Python': dlopen: dlopen(/var/folders/gw/b0cg4zm508qf_rf2m655gd3m0000gn/T/_MEIE6ec69/Python, 10): Symbol not found: _futimens
  Referenced from: /var/folders/gw/b0cg4zm508qf_rf2m655gd3m0000gn/T/_MEIE6ec69/Python (which was built for Mac OS X 10.13)
  Expected in: /usr/lib/libSystem.B.dylib
 in /var/folders/gw/b0cg4zm508qf_rf2m655gd3m0000gn/T/_MEIE6ec69/Python
exit status 255
Error compiling for board Adafruit Bluefruit nRF52832 Feather.

It is probably due to the pre-built adafruit-nrfutil cannot run on your Mac. The binary is generated on MacOS 10.13, if your Mac is older than that. Please update your macOS, or you could follow this repo's readme here https://github.com/adafruit/Adafruit_nRF52_nrfutil to manual install it ( tried with pip3 first, or install from source if it doesn't work). Then use the installed binary to replace the one in the BSP.

CircuitPython is a programming language designed to simplify experimenting and learning to program on low-cost microcontroller boards. It makes getting started easier than ever with no upfront desktop downloads needed. Once you get your board set up, open any text editor, and get started editing code. It's that simple.

CircuitPython is based on Python

Python is the fastest growing programming language. It's taught in schools and universities. It's a high-level programming language which means it's designed to be easier to read, write and maintain. It supports modules and packages which means it's easy to reuse your code for other projects. It has a built in interpreter which means there are no extra steps, like compiling, to get your code to work. And of course, Python is Open Source Software which means it's free for anyone to use, modify or improve upon.

CircuitPython adds hardware support to all of these amazing features. If you already have Python knowledge, you can easily apply that to using CircuitPython. If you have no previous experience, it's really simple to get started!

Why would I use CircuitPython?

CircuitPython is designed to run on microcontroller boards. A microcontroller board is a board with a microcontroller chip that's essentially an itty-bitty all-in-one computer. The board you're holding is a microcontroller board! CircuitPython is easy to use because all you need is that little board, a USB cable, and a computer with a USB connection. But that's only the beginning.

Other reasons to use CircuitPython include:

  • You want to get up and running quickly. Create a file, edit your code, save the file, and it runs immediately. There is no compiling, no downloading and no uploading needed.
  • You're new to programming. CircuitPython is designed with education in mind. It's easy to start learning how to program and you get immediate feedback from the board.
  • Easily update your code. Since your code lives on the disk drive, you can edit it whenever you like, you can also keep multiple files around for easy experimentation.
  • The serial console and REPL. These allow for live feedback from your code and interactive programming.
  • File storage. The internal storage for CircuitPython makes it great for data-logging, playing audio clips, and otherwise interacting with files.
  • Strong hardware support. There are many libraries and drivers for sensors, breakout boards and other external components.
  • It's Python! Python is the fastest-growing programming language. It's taught in schools and universities. CircuitPython is almost-completely compatible with Python. It simply adds hardware support.

This is just the beginning. CircuitPython continues to evolve, and is constantly being updated. We welcome and encourage feedback from the community, and we incorporate this into how we are developing CircuitPython. That's the core of the open source concept. This makes CircuitPython better for you and everyone who uses it!

CircuitPython is a derivative of MicroPython designed to simplify experimentation and education on low-cost microcontrollers. It makes it easier than ever to get prototyping by requiring no upfront desktop software downloads. Simply copy and edit files on the CIRCUITPY drive to iterate.

Set up CircuitPython Quick Start!

Follow this quick step-by-step for super-fast Python power :)

Further Information

For more detailed info on installing CircuitPython, check out Installing CircuitPython.

Click the link above and download the latest UF2 file.

Download and save it to your desktop (or wherever is handy).

Plug your Itsy nRF52840 into your computer using a known-good USB cable.

A lot of people end up using charge-only USB cables and it is very frustrating! So make sure you have a USB cable you know is good for data sync.

In the image, the Reset button is indicated by the magenta arrow, and the BTLE status LED is indicated by the green arrow.

Double-click the Reset button on your board (magenta arrow), and you will see the BTLE LED (green arrow) will pulse quickly then slowly blue. If the DotStar LED turns red, check the USB cable, try another USB port, etc.

If double-clicking doesn't work the first time, try again. Sometimes it can take a few tries to get the rhythm right!

You will see a new disk drive appear called ITSY840BOOT.

Drag the adafruit_circuitpython_etc.uf2 file to ITSY840BOOT.

The LED will flash. Then, the ITSY840BOOT drive will disappear and a new disk drive called CIRCUITPY will appear.

That's it, you're done! :)

Mu is a simple code editor that works with the Adafruit CircuitPython boards. It's written in Python and works on Windows, MacOS, Linux and Raspberry Pi. The serial console is built right in so you get immediate feedback from your board's serial output!

Mu is our recommended editor - please use it (unless you are an experienced coder with a favorite editor already!)

Download and Install Mu

Download Mu from https://codewith.mu. Click the Download or Start Here links there for downloads and installation instructions. The website has a wealth of other information, including extensive tutorials and and how-to's.

 

Using Mu

The first time you start Mu, you will be prompted to select your 'mode' - you can always change your mind later. For now please select Adafruit!

The current mode is displayed in the lower right corner of the window, next to the "gear" icon. If the mode says "Microbit" or something else, click on that and then choose "Adafruit" in the dialog box that appears.

Mu attempts to auto-detect your board, so please plug in your CircuitPython device and make sure it shows up as a CIRCUITPY drive before starting Mu

Now you're ready to code! Lets keep going....

One of the best things about CircuitPython is how simple it is to get code up and running. In this section, we're going to cover how to create and edit your first CircuitPython program.

To create and edit code, all you'll need is an editor. There are many options. We strongly recommend using Mu! It's designed for CircuitPython, and it's really simple and easy to use, with a built in serial console!

If you don't or can't use Mu, there are basic text editors built into every operating system such as Notepad on Windows, TextEdit on Mac, and gedit on Linux. However, many of these editors don't write back changes immediately to files that you edit. That can cause problems when using CircuitPython. See the Editing Code section below. If you want to skip that section for now, make sure you do "Eject" or "Safe Remove" on Windows or "sync" on Linux after writing a file if you aren't using Mu. (This is not a problem on MacOS.)

Creating Code

Open your editor, and create a new file. If you are using Mu, click the New button in the top left

Copy and paste the following code into your editor:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    time.sleep(0.5)
    led.value = False
    time.sleep(0.5)
The QT Py does not have a D13 LED! There is an addressable RGB NeoPixel LED. This example will NOT work on the QT Py!
If you are using Adafruit CLUE, you will need to edit the code to use board.D17 as shown below!

For Adafruit CLUE, you'll need to use board.D17 instead of board.D13. The rest of the code remains the same. Make the following change to the led = line:

Download: file
led = digitalio.DigitalInOut(board.D17)
If you are using Adafruit ItsyBitsy nRF52840, you will need to edit the code to use board.BLUE_LED as shown below!

For Adafruit ItsyBitsy nRF52840, you'll need to use board.BLUE_LED instead of board.D13. The rest of the code remains the same. Make the following change to the led = line:

Download: file
led = digitalio.DigitalInOut(board.BLUE_LED)

It will look like this - note that under the while True: line, the next four lines have spaces to indent them, but they're indented exactly the same amount. All other lines have no spaces before the text.

Save this file as code.py on your CIRCUITPY drive.

On each board (except the ItsyBitsy nRF52840) you'll find a tiny red LED. On the ItsyBitsy nRF52840, you'll find a tiny blue LED.

The little LED should now be blinking. Once per second.

Congratulations, you've just run your first CircuitPython program!

Editing Code

To edit code, open the code.py file on your CIRCUITPY drive into your editor.

 

Make the desired changes to your code. Save the file. That's it!

Your code changes are run as soon as the file is done saving.

There's just one warning we have to give you before we continue...

Don't Click Reset or Unplug!

The CircuitPython code on your board detects when the files are changed or written and will automatically re-start your code. This makes coding very fast because you save, and it re-runs.

However, you must wait until the file is done being saved before unplugging or resetting your board! On Windows using some editors this can sometimes take up to 90 seconds, on Linux it can take 30 seconds to complete because the text editor does not save the file completely. Mac OS does not seem to have this delay, which is nice!

This is really important to be aware of. If you unplug or reset the board before your computer finishes writing the file to your board, you can corrupt the drive. If this happens, you may lose the code you've written, so it's important to backup your code to your computer regularly.

There are a few ways to avoid this:

1. Use an editor that writes out the file completely when you save it.

Recommended editors:

Recommended only with particular settings or with add-ons:

  • vim / vi safely writes all changes. But set up vim to not write swapfiles (.swp files: temporary records of your edits) to CIRCUITPY. Run vim with vim -n, set the no swapfile option, or set the directory option to write swapfiles elsewhere. Otherwise the swapfile writes trigger restarts of your program.
  • The PyCharm IDE is safe if "Safe Write" is turned on in Settings->System Settings->Synchronization (true by default).
  • If you are using Atom, install the  fsync-on-save package so that it will always write out all changes to files on CIRCUITPY.
  • SlickEdit works only if you add a macro to flush the disk.

We don't recommend these editors:

  • notepad (the default Windows editor) and Notepad++ can be slow to write, so we recommend the editors above! If you are using notepad, be sure to eject the drive (see below)
  • IDLE in Python 3.8.0 or earlier does not force out changes immediately
  • nano (on Linux) does not force out changes
  • geany (on Linux) does not force out changes
  • Anything else - we haven't tested other editors so please use a recommended one!

2. Eject or Sync the Drive After Writing

If you are using one of our not-recommended-editors, not all is lost! You can still make it work.

On Windows, you can Eject or Safe Remove the CIRCUITPY drive. It won't actually eject, but it will force the operating system to save your file to disk. On Linux, use the sync command in a terminal to force the write to disk.

Oh No I Did Something Wrong and Now The CIRCUITPY Drive Doesn't Show Up!!!

Don't worry! Corrupting the drive isn't the end of the world (or your board!). If this happens, follow the steps found on the Troubleshooting page of every board guide to get your board up and running again.

Back to Editing Code...

Now! Let's try editing the program you added to your board. Open your code.py file into your editor. We'll make a simple change. Change the first 0.5 to 0.1. The code should look like this:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    time.sleep(0.1)
    led.value = False
    time.sleep(0.5)

Leave the rest of the code as-is. Save your file. See what happens to the LED on your board? Something changed! Do you know why? Let's find out! 

Exploring Your First CircuitPython Program

First, we'll take a look at the code we're editing.

Here is the original code again:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    time.sleep(0.5)
    led.value = False
    time.sleep(0.5)

Imports & Libraries

Each CircuitPython program you run needs to have a lot of information to work. The reason CircuitPython is so simple to use is that most of that information is stored in other files and works in the background. These files are called libraries. Some of them are built into CircuitPython. Others are stored on your CIRCUITPY drive in a folder called lib.

Download: file
import board
import digitalio
import time

The import statements tells the board that you're going to use a particular library in your code. In this example, we imported three libraries: board, digitalio, and time. All three of these libraries are built into CircuitPython, so no separate files are needed. That's one of the things that makes this an excellent first example. You don't need any thing extra to make it work! board gives you access to the hardware on your board, digitalio lets you access that hardware as inputs/outputs and time let's you pass time by 'sleeping'

Setting Up The LED

The next two lines setup the code to use the LED.

Download: file
led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

Your board knows the red LED as D13. So, we initialise that pin, and we set it to output. We set led to equal the rest of that information so we don't have to type it all out again later in our code.

Loop-de-loops

The third section starts with a  while statement. while True: essentially means, "forever do the following:". while True: creates a loop. Code will loop "while" the condition is "true" (vs. false), and as True is never False, the code will loop forever. All code that is indented under while True: is "inside" the loop.

Inside our loop, we have four items:

Download: file
while True:
    led.value = True
    time.sleep(0.5)
    led.value = False
    time.sleep(0.5)

First, we have led.value = True. This line tells the LED to turn on. On the next line, we have time.sleep(0.5). This line is telling CircuitPython to pause running code for 0.5 seconds. Since this is between turning the led on and off, the led will be on for 0.5 seconds.

The next two lines are similar. led.value = False tells the LED to turn off, and time.sleep(0.5) tells CircuitPython to pause for another 0.5 seconds. This occurs between turning the led off and back on so the LED will be off for 0.5 seconds too.

Then the loop will begin again, and continue to do so as long as the code is running!

So, when you changed the first 0.5 to 0.1, you decreased the amount of time that the code leaves the LED on. So it blinks on really quickly before turning off!

Great job! You've edited code in a CircuitPython program!

What if I don't have the loop?

If you don't have the loop, the code will run to the end and exit. This can lead to some unexpected behavior in simple programs like this since the "exit" also resets the state of the hardware. This is a different behavior than running commands via REPL. So if you are writing a simple program that doesn't seem to work, you may need to add a loop to the end so the program doesn't exit.

The simplest loop would be:

while True:

    pass

And remember - you can press <CTRL><C> to exit the loop.

See also the Behavior section in the docs.

More Changes

We don't have to stop there! Let's keep going. Change the second 0.5 to 0.1 so it looks like this:

Download: file
while True:
    led.value = True
    time.sleep(0.1)
    led.value = False
    time.sleep(0.1)

Now it blinks really fast! You decreased the both time that the code leaves the LED on and off!

Now try increasing both of the 0.1 to 1. Your LED will blink much more slowly because you've increased the amount of time that the LED is turned on and off.

Well done! You're doing great! You're ready to start into new examples and edit them to see what happens! These were simple changes, but major changes are done using the same process. Make your desired change, save it, and get the results. That's really all there is to it!

Naming Your Program File

CircuitPython looks for a code file on the board to run. There are four options: code.txt, code.py, main.txt and main.py. CircuitPython looks for those files, in that order, and then runs the first one it finds. While we suggest using code.py as your code file, it is important to know that the other options exist. If your program doesn't seem to be updating as you work, make sure you haven't created another code file that's being read instead of the one you're working on.

One of the staples of CircuitPython (and programming in general!) is something called a "print statement". This is a line you include in your code that causes your code to output text. A print statement in CircuitPython looks like this:

print("Hello, world!")

This line would result in:

Hello, world!

However, these print statements need somewhere to display. That's where the serial console comes in!

The serial console receives output from your CircuitPython board sent over USB and displays it so you can see it. This is necessary when you've included a print statement in your code and you'd like to see what you printed. It is also helpful for troubleshooting errors, because your board will send errors and the serial console will print those too.

The serial console requires a terminal program. A terminal is a program that gives you a text-based interface to perform various tasks.

If you're on Linux, and are seeing multi-second delays connecting to the serial console, or are seeing "AT" and other gibberish when you connect, then the modemmanager service might be interfering. Just remove it; it doesn't have much use unless you're still using dial-up modems. To remove, type this command at a shell:
Download: file
sudo apt purge modemmanager

Are you using Mu?

If so, good news! The serial console is built into Mu and will autodetect your board making using the REPL really really easy.

Please note that Mu does yet not work with nRF52 or ESP8266-based CircuitPython boards, skip down to the next section for details on using a terminal program.

First, make sure your CircuitPython board is plugged in. If you are using Windows 7, make sure you installed the drivers.

Once in Mu, look for the Serial button in the menu and click it.

Setting Permissions on Linux

On Linux, if you see an error box something like the one below when you press the Serial button, you need to add yourself to a user group to have permission to connect to the serial console.

On Ubuntu and Debian, add yourself to the dialout group by doing:

sudo adduser $USER dialout

After running the command above, reboot your machine to gain access to the group. On other Linux distributions, the group you need may be different. See Advanced Serial Console on Mac and Linux for details on how to add yourself to the right group.

Using Something Else?

If you're not using Mu to edit, are using ESP8266 or nRF52 CircuitPython, or if for some reason you are not a fan of the built in serial console, you can run the serial console as a separate program.

Windows requires you to download a terminal program, check out this page for more details

Mac and Linux both have one built in, though other options are available for download, check this page for more details

Once you've successfully connected to the serial console, it's time to start using it.

The code you wrote earlier has no output to the serial console. So, we're going to edit it to create some output.

Open your code.py file into your editor, and include a print statement. You can print anything you like! Just include your phrase between the quotation marks inside the parentheses. For example:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    print("Hello, CircuitPython!")
    led.value = True
    time.sleep(1)
    led.value = False
    time.sleep(1)

Save your file.

Now, let's go take a look at the window with our connection to the serial console.

Excellent! Our print statement is showing up in our console! Try changing the printed text to something else.

Keep your serial console window where you can see it. Save your file. You'll see what the serial console displays when the board reboots. Then you'll see your new change!

The Traceback (most recent call last): is telling you the last thing your board was doing before you saved your file. This is normal behavior and will happen every time the board resets. This is really handy for troubleshooting. Let's introduce an error so we can see how it is used.

Delete the e at the end of True from the line led.value = True so that it says led.value = Tru

Save your file. You will notice that your red LED will stop blinking, and you may have a colored status LED blinking at you. This is because the code is no longer correct and can no longer run properly. We need to fix it!

Usually when you run into errors, it's not because you introduced them on purpose. You may have 200 lines of code, and have no idea where your error could be hiding. This is where the serial console can help. Let's take a look!

The Traceback (most recent call last): is telling you that the last thing it was able to run was line 10 in your code. The next line is your error: NameError: name 'Tru' is not defined. This error might not mean a lot to you, but combined with knowing the issue is on line 10, it gives you a great place to start!

Go back to your code, and take a look at line 10. Obviously, you know what the problem is already. But if you didn't, you'd want to look at line 10 and see if you could figure it out. If you're still unsure, try googling the error to get some help. In this case, you know what to look for. You spelled True wrong. Fix the typo and save your file.

Nice job fixing the error! Your serial console is streaming and your red LED Is blinking again.

The serial console will display any output generated by your code. Some sensors, such as a humidity sensor or a thermistor, receive data and you can use print statements to display that information. You can also use print statements for troubleshooting. If your code isn't working, and you want to know where it's failing, you can put print statements in various places to see where it stops printing.

The serial console has many uses, and is an amazing tool overall for learning and programming!

The other feature of the serial connection is the Read-Evaluate-Print-Loop, or REPL. The REPL allows you to enter individual lines of code and have them run immediately. It's really handy if you're running into trouble with a particular program and can't figure out why. It's interactive so it's great for testing new ideas.

To use the REPL, you first need to be connected to the serial console. Once that connection has been established, you'll want to press Ctrl + C.

If there is code running, it will stop and you'll see Press any key to enter the REPL. Use CTRL-D to reload. Follow those instructions, and press any key on your keyboard.

The Traceback (most recent call last): is telling you the last thing your board was doing before you pressed Ctrl + C and interrupted it. The KeyboardInterrupt is you pressing Ctrl + C. This information can be handy when troubleshooting, but for now, don't worry about it. Just note that it is expected behavior.

If there is no code running, you will enter the REPL immediately after pressing Ctrl + C. There is no information about what your board was doing before you interrupted it because there is no code running.

Either way, once you press a key you'll see a >>> prompt welcoming you to the REPL!

If you have trouble getting to the >>> prompt, try pressing Ctrl + C a few more times.

The first thing you get from the REPL is information about your board.

This line tells you the version of CircuitPython you're using and when it was released. Next, it gives you the type of board you're using and the type of microcontroller the board uses. Each part of this may be different for your board depending on the versions you're working with.

This is followed by the CircuitPython prompt.

From this prompt you can run all sorts of commands and code. The first thing we'll do is run help(). This will tell us where to start exploring the REPL. To run code in the REPL, type it in next to the REPL prompt.

Type help() next to the prompt in the REPL.

Then press enter. You should then see a message.

First part of the message is another reference to the version of CircuitPython you're using. Second, a URL for the CircuitPython related project guides. Then... wait. What's this? To list built-in modules, please do `help("modules")`. Remember the libraries you learned about while going through creating code? That's exactly what this is talking about! This is a perfect place to start. Let's take a look!

Type help("modules") into the REPL next to the prompt, and press enter.

This is a list of all the core libraries built into CircuitPython. We discussed how board contains all of the pins on the board that you can use in your code. From the REPL, you are able to see that list!

Type import board into the REPL and press enter. It'll go to a new prompt. It might look like nothing happened, but that's not the case! If you recall, the import statement simply tells the code to expect to do something with that module. In this case, it's telling the REPL that you plan to do something with that module.

Next, type dir(board) into the REPL and press enter.

This is a list of all of the pins on your board that are available for you to use in your code. Each board's list will differ slightly depending on the number of pins available. Do you see D13? That's the pin you used to blink the red LED!

The REPL can also be used to run code. Be aware that any code you enter into the REPL isn't saved anywhere. If you're testing something new that you'd like to keep, make sure you have it saved somewhere on your computer as well!

Every programmer in every programming language starts with a piece of code that says, "Hello, World." We're going to say hello to something else. Type into the REPL:

print("Hello, CircuitPython!")

Then press enter.

That's all there is to running code in the REPL! Nice job!

You can write single lines of code that run stand-alone. You can also write entire programs into the REPL to test them. As we said though, remember that nothing typed into the REPL is saved.

There's a lot the REPL can do for you. It's great for testing new ideas if you want to see if a few new lines of code will work. It's fantastic for troubleshooting code by entering it one line at a time and finding out where it fails. It lets you see what libraries are available and explore those libraries.

Try typing more into the REPL to see what happens!

Returning to the serial console

When you're ready to leave the REPL and return to the serial console, simply press Ctrl + D. This will reload your board and reenter the serial console. You will restart the program you had running before entering the REPL. In the console window, you'll see any output from the program you had running. And if your program was affecting anything visual on the board, you'll see that start up again as well.

You can return to the REPL at any time!

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit https://circuitpython.org/downloads to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit https://circuitpython.org/libraries to download the latest Library Bundle.

Each CircuitPython program you run needs to have a lot of information to work. The reason CircuitPython is so simple to use is that most of that information is stored in other files and works in the background. These files are called libraries. Some of them are built into CircuitPython. Others are stored on your CIRCUITPY drive in a folder called lib. Part of what makes CircuitPython so awesome is its ability to store code separately from the firmware itself. Storing code separately from the firmware makes it easier to update both the code you write and the libraries you depend.

Your board may ship with a lib folder already, it's in the base directory of the drive. If not, simply create the folder yourself. When you first install CircuitPython, an empty lib directory will be created for you.

CircuitPython libraries work in the same way as regular Python modules so the Python docs are a great reference for how it all should work. In Python terms, we can place our library files in the lib directory because its part of the Python path by default.

One downside of this approach of separate libraries is that they are not built in. To use them, one needs to copy them to the CIRCUITPY drive before they can be used. Fortunately, we provide a bundle full of our libraries.

Our bundle and releases also feature optimized versions of the libraries with the .mpy file extension. These files take less space on the drive and have a smaller memory footprint as they are loaded.

Installing the CircuitPython Library Bundle

We're constantly updating and improving our libraries, so we don't (at this time) ship our CircuitPython boards with the full library bundle. Instead, you can find example code in the guides for your board that depends on external libraries. Some of these libraries may be available from us at Adafruit, some may be written by community members!

Either way, as you start to explore CircuitPython, you'll want to know how to get libraries on board.

You can grab the latest Adafruit CircuitPython Bundle release by clicking the button below.

Note: Match up the bundle version with the version of CircuitPython you are running - 3.x library for running any version of CircuitPython 3, 4.x for running any version of CircuitPython 4, etc. If you mix libraries with major CircuitPython versions, you will most likely get errors due to changes in library interfaces possible during major version changes.

If you need another version, you can also visit the bundle release page which will let you select exactly what version you're looking for, as well as information about changes.

Either way, download the version that matches your CircuitPython firmware version. If you don't know the version, look at the initial prompt in the CircuitPython REPL, which reports the version. For example, if you're running v4.0.1, download the 4.x library bundle. There's also a py bundle which contains the uncompressed python files, you probably don't want that unless you are doing advanced work on libraries.

After downloading the zip, extract its contents. This is usually done by double clicking on the zip. On Mac OSX, it places the file in the same directory as the zip.

Open the bundle folder. Inside you'll find two information files, and two folders. One folder is the lib bundle, and the other folder is the examples bundle.

Now open the lib folder. When you open the folder, you'll see a large number of mpy files and folders

Example Files

All example files from each library are now included in the bundles, as well as an examples-only bundle. These are included for two main reasons:

  • Allow for quick testing of devices.
  • Provide an example base of code, that is easily built upon for individualized purposes.

Copying Libraries to Your Board

First you'll want to create a lib folder on your CIRCUITPY drive. Open the drive, right click, choose the option to create a new folder, and call it lib. Then, open the lib folder you extracted from the downloaded zip. Inside you'll find a number of folders and .mpy files. Find the library you'd like to use, and copy it to the lib folder on CIRCUITPY.

This also applies to example files. They are only supplied as raw .py files, so they may need to be converted to .mpy using the mpy-cross utility if you encounter MemoryErrors. This is discussed in the CircuitPython Essentials Guide. Usage is the same as described above in the Express Boards section. Note: If you do not place examples in a separate folder, you would remove the examples from the import statement.

Example: ImportError Due to Missing Library

If you choose to load libraries as you need them, you may write up code that tries to use a library you haven't yet loaded.  We're going to demonstrate what happens when you try to utilise a library that you don't have loaded on your board, and cover the steps required to resolve the issue.

This demonstration will only return an error if you do not have the required library loaded into the lib folder on your CIRCUITPY drive.

Let's use a modified version of the blinky example.

Download: file
import board
import time
import simpleio

led = simpleio.DigitalOut(board.D13)

while True:
    led.value = True
    time.sleep(0.5)
    led.value = False
    time.sleep(0.5)

Save this file. Nothing happens to your board. Let's check the serial console to see what's going on.

We have an ImportError. It says there is no module named 'simpleio'. That's the one we just included in our code!

Click the link above to download the correct bundle. Extract the lib folder from the downloaded bundle file. Scroll down to find simpleio.mpy. This is the library file we're looking for! Follow the steps above to load an individual library file.

The LED starts blinking again! Let's check the serial console.

No errors! Excellent. You've successfully resolved an ImportError!

If you run into this error in the future, follow along with the steps above and choose the library that matches the one you're missing.

Library Install on Non-Express Boards

If you have a Trinket M0 or Gemma M0, you'll want to follow the same steps in the example above to install libraries as you need them. You don't always need to wait for an ImportError as you probably know what library you added to your code. Simply open the lib folder you downloaded, find the library you need, and drag it to the lib folder on your CIRCUITPY drive.

You may end up running out of space on your Trinket M0 or Gemma M0 even if you only load libraries as you need them. There are a number of steps you can use to try to resolve this issue. You'll find them in the Troubleshooting page in the Learn guides for your board.

Updating CircuitPython Libraries/Examples

Libraries and examples are updated from time to time, and it's important to update the files you have on your CIRCUITPY drive.

To update a single library or example, follow the same steps above. When you drag the library file to your lib folder, it will ask if you want to replace it. Say yes. That's it!

A new library bundle is released every time there's an update to a library. Updates include things like bug fixes and new features. It's important to check in every so often to see if the libraries you're using have been updated.

These are some of the common questions regarding CircuitPython and CircuitPython microcontrollers.

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit https://circuitpython.org/downloads to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit https://circuitpython.org/libraries to download the latest Library Bundle.

I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 2.x and 3.x library bundles. We highly encourage you to update CircuitPython to the latest version and use the current version of the libraries. However, if for some reason you cannot update, you can find the last available 2.x build here and the last available 3.x build here.

Is ESP8266 or ESP32 supported in CircuitPython? Why not?

We are dropping ESP8266 support as of 4.x - For more information please read about it here!

https://learn.adafruit.com/welcome-to-circuitpython/circuitpython-for-esp8266

Is there asyncio support in CircuitPython

We do not have asyncio support in CircuitPython at this time

My RGB NeoPixel/DotStar LED is blinking funny colors - what does it mean?

The status LED can tell you what's going on with your CircuitPython board. Read more here for what the colors mean!

What is a MemoryError?

Memory allocation errors happen when you're trying to store too much on the board. The CircuitPython microcontroller boards have a limited amount of memory available. You can have about 250 lines of code on the M0 Express boards. If you try to import too many libraries, a combination of large libraries, or run a program with too many lines of code, your code will fail to run and you will receive a MemoryError in the serial console (REPL).

What do I do when I encounter a MemoryError?

Try resetting your board. Each time you reset the board, it reallocates the memory. While this is unlikely to resolve your issue, it's a simple step and is worth trying.

Make sure you are using .mpy versions of libraries. All of the CircuitPython libraries are available in the bundle in a .mpy format which takes up less memory than .py format. Be sure that you're using the latest library bundle for your version of CircuitPython.

If that does not resolve your issue, try shortening your code. Shorten comments, remove extraneous or unneeded code, or any other clean up you can do to shorten your code. If you're using a lot of functions, you could try moving those into a separate library, creating a .mpy of that library, and importing it into your code.

You can turn your entire file into a .mpy and import that into code.py. This means you will be unable to edit your code live on the board, but it can save you space.

Can the order of my import statements affect memory?

It can because the memory gets fragmented differently depending on allocation order and the size of objects. Loading .mpy files uses less memory so its recommended to do that for files you aren't editing.

How can I create my own .mpy files?

You can make your own .mpy versions of files with mpy-cross.

You can download the CircuitPython 2.x version of mpy-cross for your operating system from the CircuitPython Releases page under the latest 2.x version.

You can build mpy-cross for CircuitPython 3.x by cloning the CircuitPython GitHub repo, and running make in the circuitpython/mpy-cross/ directory. Then run ./mpy-cross path/to/foo.py to create a foo.mpy in the same directory as the original file.

How do I check how much memory I have free?

import gc
gc.mem_free()

Will give you the number of bytes available for use.

Does CircuitPython support interrupts?

No. CircuitPython does not currently support interrupts. We do not have an estimated time for when they will be included.

Does Feather M0 support WINC1500?

No, WINC1500 will not fit into the M0 flash space.

Can AVRs such as ATmega328 or ATmega2560 run CircuitPython?

No.

Commonly Used Acronyms

CP or CPy = CircuitPython
CPC = Circuit Playground Classic
CPX = Circuit Playground Express

CircuitPython is a programming language that's super simple to get started with and great for learning. It runs on microcontrollers and works out of the box. You can plug it in and get started with any text editor. The best part? CircuitPython comes with an amazing, supportive community.

Everyone is welcome! CircuitPython is Open Source. This means it's available for anyone to use, edit, copy and improve upon. This also means CircuitPython becomes better because of you being a part of it. It doesn't matter whether this is your first microcontroller board or you're a computer engineer, you have something important to offer the Adafruit CircuitPython community. We're going to highlight some of the many ways you can be a part of it!

Adafruit Discord

The Adafruit Discord server is the best place to start. Discord is where the community comes together to volunteer and provide live support of all kinds. From general discussion to detailed problem solving, and everything in between, Discord is a digital maker space with makers from around the world.

There are many different channels so you can choose the one best suited to your needs. Each channel is shown on Discord as "#channelname". There's the #help-with-projects channel for assistance with your current project or help coming up with ideas for your next one. There's the #showandtell channel for showing off your newest creation. Don't be afraid to ask a question in any channel! If you're unsure, #general is a great place to start. If another channel is more likely to provide you with a better answer, someone will guide you.

The help with CircuitPython channel is where to go with your CircuitPython questions. #help-with-circuitpython is there for new users and developers alike so feel free to ask a question or post a comment! Everyone of any experience level is welcome to join in on the conversation. We'd love to hear what you have to say! The #circuitpython channel is available for development discussions as well.

The easiest way to contribute to the community is to assist others on Discord. Supporting others doesn't always mean answering questions. Join in celebrating successes! Celebrate your mistakes! Sometimes just hearing that someone else has gone through a similar struggle can be enough to keep a maker moving forward.

The Adafruit Discord is the 24x7x365 hackerspace that you can bring your granddaughter to.

Visit https://adafru.it/discord to sign up for Discord. We're looking forward to meeting you!

Adafruit Forums

The Adafruit Forums are the perfect place for support. Adafruit has wonderful paid support folks to answer any questions you may have. Whether your hardware is giving you issues or your code doesn't seem to be working, the forums are always there for you to ask. You need an Adafruit account to post to the forums. You can use the same account you use to order from Adafruit.

While Discord may provide you with quicker responses than the forums, the forums are a more reliable source of information. If you want to be certain you're getting an Adafruit-supported answer, the forums are the best place to be.

There are forum categories that cover all kinds of topics, including everything Adafruit. The Adafruit CircuitPython and MicroPython category under "Supported Products & Projects" is the best place to post your CircuitPython questions.

Be sure to include the steps you took to get to where you are. If it involves wiring, post a picture! If your code is giving you trouble, include your code in your post! These are great ways to make sure that there's enough information to help you with your issue.

You might think you're just getting started, but you definitely know something that someone else doesn't. The great thing about the forums is that you can help others too! Everyone is welcome and encouraged to provide constructive feedback to any of the posted questions. This is an excellent way to contribute to the community and share your knowledge!

Adafruit Github

Whether you're just beginning or are life-long programmer who would like to contribute, there are ways for everyone to be a part of building CircuitPython. GitHub is the best source of ways to contribute to CircuitPython itself. If you need an account, visit https://github.com/ and sign up.

If you're new to GitHub or programming in general, there are great opportunities for you. Head over to adafruit/circuitpython on GitHub, click on "Issues", and you'll find a list that includes issues labeled "good first issue". These are things we've identified as something that someone with any level of experience can help with. These issues include options like updating documentation, providing feedback, and fixing simple bugs.

Already experienced and looking for a challenge? Checkout the rest of the issues list and you'll find plenty of ways to contribute. You'll find everything from new driver requests to core module updates. There's plenty of opportunities for everyone at any level!

When working with CircuitPython, you may find problems. If you find a bug, that's great! We love bugs! Posting a detailed issue to GitHub is an invaluable way to contribute to improving CircuitPython. Be sure to include the steps to replicate the issue as well as any other information you think is relevant. The more detail, the better!

Testing new software is easy and incredibly helpful. Simply load the newest version of CircuitPython or a library onto your CircuitPython hardware, and use it. Let us know about any problems you find by posting a new issue to GitHub. Software testing on both current and beta releases is a very important part of contributing CircuitPython. We can't possibly find all the problems ourselves! We need your help to make CircuitPython even better.

On GitHub, you can submit feature requests, provide feedback, report problems and much more. If you have questions, remember that Discord and the Forums are both there for help!

ReadTheDocs

ReadTheDocs is a an excellent resource for a more in depth look at CircuitPython. This is where you'll find things like API documentation and details about core modules. There is also a Design Guide that includes contribution guidelines for CircuitPython.

RTD gives you access to a low level look at CircuitPython. There are details about each of the core modules. Each module lists the available libraries. Each module library page lists the available parameters and an explanation for each. In many cases, you'll find quick code examples to help you understand how the modules and parameters work, however it won't have detailed explanations like the Learn Guides. If you want help understanding what's going on behind the scenes in any CircuitPython code you're writing, ReadTheDocs is there to help!

Windows 7 Driver

If you're using Windows 7, use the link below to download the driver package. You will not need to install drivers on Mac, Linux or Windows 10.

What's the COM?

First, you'll want to find out which serial port your board is using. When you plug your board in to USB on your computer, it connects to a serial port. The port is like a door through which your board can communicate with your computer using USB.

We'll use Windows Device Manager to determine which port the board is using. The easiest way to determine which port the board is using is to first check without the board plugged in. Open Device Manager. Click on Ports (COM & LPT). You should find something already in that list with (COM#) after it where # is a number.

Now plug in your board. The Device Manager list will refresh and a new item will appear under Ports (COM & LPT). You'll find a different (COM#) after this item in the list.

Sometimes the item will refer to the name of the board. Other times it may be called something like USB Serial Device, as seen in the image above. Either way, there is a new (COM#) following the name. This is the port your board is using.

Install Putty

If you're using Windows, you'll need to download a terminal program. We're going to use PuTTY.

The first thing to do is download the latest version of PuTTY. You'll want to download the Windows installer file. It is most likely that you'll need the 64-bit version. Download the file and install the program on your machine. If you run into issues, you can try downloading the 32-bit version instead. However, the 64-bit version will work on most PCs.

Now you need to open PuTTY.

  • Under Connection type: choose the button next to Serial.
  • In the box under Serial line, enter the serial port you found that your board is using.
  • In the box under Speed, enter 115200. This called the baud rate, which is the speed in bits per second that data is sent over the serial connection. For boards with built in USB it doesn't matter so much but for ESP8266 and other board with a separate chip, the speed required by the board is 115200 bits per second. So you might as well just use 115200!

If you want to save those settings for later, use the options under Load, save or delete a stored session. Enter a name in the box under Saved Sessions, and click the Save button on the right.

Once your settings are entered, you're ready to connect to the serial console. Click "Open" at the bottom of the window. A new window will open.

If no code is running, the window will either be blank or will look like the window above. Now you're ready to see the results of your code.

Great job! You've connected to the serial console!

Connecting to the serial console on Mac and Linux uses essentially the same process. Neither operating system needs drivers installed. On MacOSX, Terminal comes installed. On Linux, there are a variety such as gnome-terminal (called Terminal) or Konsole on KDE.

What's the Port?

First you'll want to find out which serial port your board is using. When you plug your board in to USB on your computer, it connects to a serial port. The port is like a door through which your board can communicate with your computer using USB.

We're going to use Terminal to determine what port the board is using. The easiest way to determine which port the board is using is to first check without the board plugged in. On Mac, open Terminal and type the following:

ls /dev/tty.*

Each serial connection shows up in the /dev/ directory. It has a name that starts with tty.. The command ls shows you a list of items in a directory. You can use * as a wildcard, to search for files that start with the same letters but end in something different. In this case, we're asking to see all of the listings in /dev/ that start with tty. and end in anything. This will show us the current serial connections.

For Linux, the procedure is the same, however, the name is slightly different. If you're using Linux, you'll type:

ls /dev/ttyACM*

The concept is the same with Linux. We are asking to see the listings in the /dev/ folder, starting with ttyACM and ending with anything. This will show you the current serial connections. In the example below, the error is indicating that are no current serial connections starting with ttyACM.

Now, plug your board. Using Mac, type:

ls /dev/tty.*

This will show you the current serial connections, which will now include your board.

Using Mac, a new listing has appeared called /dev/tty.usbmodem141441. The tty.usbmodem141441 part of this listing is the name the example board is using. Yours will be called something similar.

Using Linux, type:

ls /dev/ttyACM*

This will show you the current serial connections, which will now include your board.

Using Linux, a new listing has appeared called /dev/ttyACM0. The ttyACM0 part of this listing is the name the example board is using. Yours will be called something similar.

Connect with screen

Now that you know the name your board is using, you're ready connect to the serial console. We're going to use a command called screen. The screen command is included with MacOS. Linux users may need to install it using their package manager. To connect to the serial console, use Terminal. Type the following command, replacing board_name with the name you found your board is using:

screen /dev/tty.board_name 115200

The first part of this establishes using the screen command. The second part tells screen the name of the board you're trying to use. The third part tells screen what baud rate to use for the serial connection. The baud rate is the speed in bits per second that data is sent over the serial connection. In this case, the speed required by the board is 115200 bits per second.

circuitpython_ScreenCommandMac.png
MacOS screen command using example board name

Press enter to run the command. It will open in the same window. If no code is running, the window will be blank. Otherwise, you'll see the output of your code.

Great job! You've connected to the serial console!

Permissions on Linux

If you try to run screen and it doesn't work, then you may be running into an issue with permissions. Linux keeps track of users and groups and what they are allowed to do and not do, like access the hardware associated with the serial connection for running screen. So if you see something like this:

then you may need to grant yourself access. There are generally two ways you can do this. The first is to just run screen using the sudo command, which temporarily gives you elevated privileges.

Once you enter your password, you should be in:

The second way is to add yourself to the group associated with the hardware. To figure out what that group is, use the command ls -l as shown below. The group name is circled in red.

Then use the command adduser to add yourself to that group. You need elevated privileges to do this, so you'll need to use sudo. In the example below, the group is adm and the user is ackbar.

After you add yourself to the group, you'll need to logout and log back in, or in some cases, reboot your machine. After you log in again, verify that you have been added to the group using the command groups. If you are still not in the group, reboot and check again.

And now you should be able to run screen without using sudo.

And you're in:

The examples above use screen, but you can also use other programs, such as putty or picocom, if you prefer.

A lot of our boards can be used with multiple programming languages. For example, the Circuit Playground Express can be used with MakeCode, Code.org CS Discoveries, CircuitPython and Arduino.

Maybe you tried CircuitPython and want to go back to MakeCode or Arduino? Not a problem

You can always remove/re-install CircuitPython whenever you want! Heck, you can change your mind every day!

Backup Your Code

Before uninstalling CircuitPython, don't forget to make a backup of the code you have on the little disk drive. That means your main.py or code.py any other files, the lib folder etc. You may lose these files when you remove CircuitPython, so backups are key! Just drag the files to a folder on your laptop or desktop computer like you would with any USB drive.

Moving Circuit Playground Express to MakeCode

On the Circuit Playground Express (this currently does NOT apply to Circuit Playground Bluefruit), if you want to go back to using MakeCode, it's really easy. Visit makecode.adafruit.com and find the program you want to upload. Click Download to download the .uf2 file that is generated by MakeCode.

Now double-click your CircuitPython board until you see the onboard LED(s) turn green and the ...BOOT directory shows up.

Then find the downloaded MakeCode .uf2 file and drag it to the ...BOOT drive.

Your MakeCode is now running and CircuitPython has been removed. Going forward you only have to single click the reset button

Moving to Arduino

If you want to change your firmware to Arduino, it's also pretty easy.

Start by plugging in your board, and double-clicking reset until you get the green onboard LED(s) - just like with MakeCode

Within Arduino IDE, select the matching board, say Circuit Playground Express

Select the correct matching Port:

Create a new simple Blink sketch example:

Download: file
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin 13 as an output.
  pinMode(13, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);              // wait for a second
  digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);              // wait for a second
}

Make sure the LED(s) are still green, then click Upload to upload Blink. Once it has uploaded successfully, the serial Port will change so re-select the new Port!

Once Blink is uploaded you should no longer need to double-click to enter bootloader mode, Arduino will automatically reset when you upload

From time to time, you will run into issues when working with CircuitPython. Here are a few things you may encounter and how to resolve them.

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit https://circuitpython.org/downloads to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit https://circuitpython.org/libraries to download the latest Library Bundle.

Always Run the Latest Version of CircuitPython and Libraries

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. You need to update to the latest CircuitPython..

You need to download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then download the latest bundle.

As we release new versions of CircuitPython, we will stop providing the previous bundles as automatically created downloads on the Adafruit CircuitPython Library Bundle repo. If you must continue to use an earlier version, you can still download the appropriate version of mpy-cross from the particular release of CircuitPython on the CircuitPython repo and create your own compatible .mpy library files. However, it is best to update to the latest for both CircuitPython and the library bundle.

I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 2.x and 3.x library bundles. We highly encourage you to update CircuitPython to the latest version and use the current version of the libraries. However, if for some reason you cannot update, you can find the last available 2.x build here and the last available 3.x build here.

CPLAYBOOT, TRINKETBOOT, FEATHERBOOT, or GEMMABOOT Drive Not Present

You may have a different board.

Only Adafruit Express boards and the Trinket M0 and Gemma M0 boards ship with the UF2 bootloader installed. Feather M0 Basic, Feather M0 Adalogger, and similar boards use a regular Arduino-compatible bootloader, which does not show a boardnameBOOT drive.

MakeCode

If you are running a MakeCode program on Circuit Playground Express, press the reset button just once to get the CPLAYBOOT drive to show up. Pressing it twice will not work.

Windows 10

Did you install the Adafruit Windows Drivers package by mistake? You don't need to install this package on Windows 10 for most Adafruit boards. The old version (v1.5) can interfere with recognizing your device. Go to Settings -> Apps and uninstall all the "Adafruit" driver programs.

Windows 7

Version 2.0.0.0 or later of the Adafruit Windows Drivers will fix the missing boardnameBOOT drive problem on Windows 7. To resolve this, first uninstall the old versions of the drivers:

  • Unplug any boards. In Uninstall or Change a Program (Control Panel->Programs->Uninstall a program), uninstall everything named "Windows Driver Package - Adafruit Industries LLC ...".

MacOS

DriveDx and its accompanything SAT SMART Driver can interfere with seeing the BOOT drive. See this forum post for how to fix the problem.

 

  • Now install the new 2.3.0.0 (or higher) Adafruit Windows Drivers Package:
  • When running the installer, you'll be shown a list of drivers to choose from. You can check and uncheck the boxes to choose which drivers to install.

You should now be done! Test by unplugging and replugging the board. You should see the CIRCUITPY drive, and when you double-click the reset button (single click on Circuit Playground Express running MakeCode), you should see the appropriate boardnameBOOT drive.

Let us know in the Adafruit support forums or on the Adafruit Discord if this does not work for you!

Windows Explorer Locks Up When Accessing boardnameBOOT Drive

On Windows, several third-party programs we know of can cause issues. The symptom is that you try to access the boardnameBOOT drive, and Windows or Windows Explorer seems to lock up. These programs are known to cause trouble:

  • AIDA64: to fix, stop the program. This problem has been reported to AIDA64. They acquired hardware to test, and released a beta version that fixes the problem. This may have been incorporated into the latest release. Please let us know in the forums if you test this.
  • Hard Disk Sentinel
  • Kaspersky anti-virus: To fix, you may need to disable Kaspersky completely. Disabling some aspects of Kaspersky does not always solve the problem. This problem has been reported to Kaspersky.
  • ESET NOD32 anti-virus: We have seen problems with at least version 9.0.386.0, solved by uninstallation.

Copying UF2 to boardnameBOOT Drive Hangs at 0% Copied

On Windows, a Western DIgital (WD) utility that comes with their external USB drives can interfere with copying UF2 files to the boardnameBOOT drive. Uninstall that utility to fix the problem.

CIRCUITPY Drive Does Not Appear

Kaspersky anti-virus can block the appearance of the CIRCUITPY drive. We haven't yet figured out a settings change that prevents this. Complete uninstallation of Kaspersky fixes the problem.

Norton anti-virus can interfere with CIRCUITPY. A user has reported this problem on Windows 7. The user turned off both Smart Firewall and Auto Protect, and CIRCUITPY then appeared.

Serial Console in Mu Not Displaying Anything

There are times when the serial console will accurately not display anything, such as, when no code is currently running, or when code with no serial output is already running before you open the console. However, if you find yourself in a situation where you feel it should be displaying something like an error, consider the following.

Depending on the size of your screen or Mu window, when you open the serial console, the serial console panel may be very small. This can be a problem. A basic CircuitPython error takes 10 lines to display!

Download: file
Auto-reload is on. Simply save files over USB to run them or enter REPL to disable.
code.py output:
Traceback (most recent call last):
  File "code.py", line 7
SyntaxError: invalid syntax



Press any key to enter the REPL. Use CTRL-D to reload.
 

More complex errors take even more lines!

Therefore, if your serial console panel is five lines tall or less, you may only see blank lines or blank lines followed by Press any key to enter the REPL. Use CTRL-D to reload.. If this is the case, you need to either mouse over the top of the panel to utilise the option to resize the serial panel, or use the scrollbar on the right side to scroll up and find your message.

This applies to any kind of serial output whether it be error messages or print statements. So before you start trying to debug your problem on the hardware side, be sure to check that you haven't simply missed the serial messages due to serial output panel height.

CircuitPython RGB Status Light

Nearly all Adafruit CircuitPython-capable boards have a single NeoPixel or DotStar RGB LED on the board that indicates the status of CircuitPython. A few boards designed before CircuitPython existed, such as the Feather M0 Basic, do not.

Circuit Playground Express and Circuit Playground Bluefruit have multiple RGB LEDs, but do NOT have a status LED. The LEDs are all green when in the bootloader. They do NOT indicate any status while running CircuitPython.

Here's what the colors and blinking mean:

  • steady GREEN: code.py (or code.txt, main.py, or main.txt) is running
  • pulsing GREEN: code.py (etc.) has finished or does not exist
  • steady YELLOW at start up: (4.0.0-alpha.5 and newer) CircuitPython is waiting for a reset to indicate that it should start in safe mode
  • pulsing YELLOW: Circuit Python is in safe mode: it crashed and restarted
  • steady WHITE: REPL is running
  • steady BLUE: boot.py is running

Colors with multiple flashes following indicate a Python exception and then indicate the line number of the error. The color of the first flash indicates the type of error:

  • GREEN: IndentationError
  • CYAN: SyntaxError
  • WHITE: NameError
  • ORANGE: OSError
  • PURPLE: ValueError
  • YELLOW: other error

These are followed by flashes indicating the line number, including place value. WHITE flashes are thousands' place, BLUE are hundreds' place, YELLOW are tens' place, and CYAN are one's place. So for example, an error on line 32 would flash YELLOW three times and then CYAN two times. Zeroes are indicated by an extra-long dark gap.

ValueError: Incompatible .mpy file.

This error occurs when importing a module that is stored as a mpy binary file that was generated by a different version of CircuitPython than the one its being loaded into. In particular, the mpy binary format changed between CircuitPython versions 2.x and 3.x, as well as between 1.x and 2.x.

So, for instance, if you upgraded to CircuitPython 3.x from 2.x you’ll need to download a newer version of the library that triggered the error on import. They are all available in the Adafruit bundle.

Make sure to download a version with 2.0.0 or higher in the filename if you're using CircuitPython version 2.2.4, and the version with 3.0.0 or higher in the filename if you're using CircuitPython version 3.0.

CIRCUITPY Drive Issues

You may find that you can no longer save files to your CIRCUITPY drive. You may find that your CIRCUITPY stops showing up in your file explorer, or shows up as NO_NAME. These are indicators that your filesystem has issues.

First check - have you used Arduino to program your board? If so, CircuitPython is no longer able to provide the USB services. Reset the board so you get a boardnameBOOT drive rather than a CIRCUITPY drive, copy the latest version of CircuitPython (.uf2) back to the board, then Reset. This may restore CIRCUITPY functionality.

If still broken - When the CIRCUITPY disk is not safely ejected before being reset by the button or being disconnected from USB, it may corrupt the flash drive. It can happen on Windows, Mac or Linux.

In this situation, the board must be completely erased and CircuitPython must be reloaded onto the board.

You WILL lose everything on the board when you complete the following steps. If possible, make a copy of your code before continuing.

Easiest Way: Use storage.erase_filesystem()

Starting with version 2.3.0, CircuitPython includes a built-in function to erase and reformat the filesystem. If you have an older version of CircuitPython on your board, you can update to the newest version to do this.

  1. Connect to the CircuitPython REPL using Mu or a terminal program.
  2. Type:
Download: file
>>> import storage
>>> storage.erase_filesystem()

CIRCUITPY will be erased and reformatted, and your board will restart. That's it!

Old Way: For the Circuit Playground Express, Feather M0 Express, and Metro M0 Express:

If you can't get to the REPL, or you're running a version of CircuitPython before 2.3.0, and you don't want to upgrade, you can do this.

       1.  Download the correct erase file:

       2.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       3.  Drag the erase .uf2 file to the boardnameBOOT drive.
       4.  The onboard NeoPixel will turn yellow or blue, indicating the erase has started.
       5.  After approximately 15 seconds, the mainboard NeoPixel will light up green. On the NeoTrellis M4 this is the first NeoPixel on the grid
       6.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       7.  Drag the appropriate latest release of CircuitPython .uf2 file to the boardnameBOOT drive.

It should reboot automatically and you should see CIRCUITPY in your file explorer again.

If the LED flashes red during step 5, it means the erase has failed. Repeat the steps starting with 2.

If you haven't already downloaded the latest release of CircuitPython for your board, check out the installation page. You'll also need to install your libraries and code!

Old Way: For Non-Express Boards with a UF2 bootloader (Gemma M0, Trinket M0):

If you can't get to the REPL, or you're running a version of CircuitPython before 2.3.0, and you don't want to upgrade, you can do this.

       1.  Download the erase file:

       2.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       3.  Drag the erase .uf2 file to the boardnameBOOT drive.
       4.  The boot LED will start flashing again, and the boardnameBOOT drive will reappear.
       5.  Drag the appropriate latest release CircuitPython .uf2 file to the boardnameBOOT drive.

It should reboot automatically and you should see CIRCUITPY in your file explorer again.

If you haven't already downloaded the latest release of CircuitPython for your board, check out the installation page You'll also need to install your libraries and code!

Old Way: For non-Express Boards without a UF2 bootloader (Feather M0 Basic Proto, Feather Adalogger, Arduino Zero):

If you are running a version of CircuitPython before 2.3.0, and you don't want to upgrade, or you can't get to the REPL, you can do this.

Just follow these directions to reload CircuitPython using bossac, which will erase and re-create CIRCUITPY.

Running Out of File Space on Non-Express Boards

The file system on the board is very tiny. (Smaller than an ancient floppy disk.) So, its likely you'll run out of space but don't panic! There are a couple ways to free up space.

The board ships with the Windows 7 serial driver too! Feel free to delete that if you don't need it or have already installed it. Its ~12KiB or so.

Delete something!

The simplest way of freeing up space is to delete files from the drive. Perhaps there are libraries in the lib folder that you aren't using anymore or test code that isn't in use. Don't delete the lib folder completely, though, just remove what you don't need.

Use tabs

One unique feature of Python is that the indentation of code matters. Usually the recommendation is to indent code with four spaces for every indent. In general, we recommend that too. However, one trick to storing more human-readable code is to use a single tab character for indentation. This approach uses 1/4 of the space for indentation and can be significant when we're counting bytes.

MacOS loves to add extra files.

Luckily you can disable some of the extra hidden files that MacOS adds by running a few commands to disable search indexing and create zero byte placeholders. Follow the steps below to maximize the amount of space available on MacOS:

Prevent & Remove MacOS Hidden Files

First find the volume name for your board.  With the board plugged in run this command in a terminal to list all the volumes:

Download: file
ls -l /Volumes

Look for a volume with a name like CIRCUITPY (the default for CircuitPython).  The full path to the volume is the /Volumes/CIRCUITPY path.

Now follow the steps from this question to run these terminal commands that stop hidden files from being created on the board:

Download: file
mdutil -i off /Volumes/CIRCUITPY
cd /Volumes/CIRCUITPY
rm -rf .{,_.}{fseventsd,Spotlight-V*,Trashes}
mkdir .fseventsd
touch .fseventsd/no_log .metadata_never_index .Trashes
cd -

Replace /Volumes/CIRCUITPY in the commands above with the full path to your board's volume if it's different.  At this point all the hidden files should be cleared from the board and some hidden files will be prevented from being created.

Alternatively, with CircuitPython 4.x and above, the special files and folders mentioned above will be created automatically if you erase and reformat the filesystem. WARNING: Save your files first! Do this in the REPL:

>>> import storage
>>> storage.erase_filesystem

However there are still some cases where hidden files will be created by MacOS.  In particular if you copy a file that was downloaded from the internet it will have special metadata that MacOS stores as a hidden file.  Luckily you can run a copy command from the terminal to copy files without this hidden metadata file.  See the steps below.

Copy Files on MacOS Without Creating Hidden Files

Once you've disabled and removed hidden files with the above commands on MacOS you need to be careful to copy files to the board with a special command that prevents future hidden files from being created.  Unfortunately you cannot use drag and drop copy in Finder because it will still create these hidden extended attribute files in some cases (for files downloaded from the internet, like Adafruit's modules).

To copy a file or folder use the -X option for the cp command in a terminal.  For example to copy a foo.mpy file to the board use a command like:

Download: file
    cp -X foo.mpy /Volumes/CIRCUITPY
  

(Replace foo.mpy with the name of the file you want to copy.) Or to copy a folder and all of its child files/folders use a command like:

Download: file
cp -rX folder_to_copy /Volumes/CIRCUITPY

If you are copying to the lib folder, or another folder, make sure it exists before copying.

Download: file
# if lib does not exist, you'll create a file named lib !
cp -X foo.mpy /Volumes/CIRCUITPY/lib
# This is safer, and will complain if a lib folder does not exist.
cp -X foo.mpy /Volumes/CIRCUITPY/lib/

Other MacOS Space-Saving Tips

If you'd like to see the amount of space used on the drive and manually delete hidden files here's how to do so.  First list the amount of space used on the CIRCUITPY drive with the df command:

Lets remove the ._ files first.

Whoa! We have 13Ki more than before! This space can now be used for libraries and code!

Guides

You've gone through the Welcome to CircuitPython guide. You've already gotten everything setup, and you've gotten CircuitPython running. Great! Now what? CircuitPython Essentials!

There are a number of core modules built into CircuitPython and commonly used libraries available. This guide will introduce you to these and show you an example of how to use each one.

Each section will present you with a piece of code designed to work with different boards, and explain how to use the code with each board. These examples work with any board designed for CircuitPython, including Circuit Playground Express, Trinket M0, Gemma M0ItsyBitsy M0 Express, ItsyBitsy M4 Express, Feather M0 Express, Feather M4 Express, Metro M4 Express,  Metro M0 Express, Trellis M4 Express, and Grand Central M4 Express.

Some examples require external components, such as switches or sensors. You'll find wiring diagrams where applicable to show you how to wire up the necessary components to work with each example.

Let's get started learning the CircuitPython Essentials!

CircuitPython comes 'with the kitchen sink' - a lot of the things you know and love about classic Python 3 (sometimes called CPython) already work. There are a few things that don't but we'll try to keep this list updated as we add more capabilities!

This is not an exhaustive list! It's simply some of the many features you can use.

Thing That Are Built In and Work

Flow Control

All the usual if, elif, else, for, while work just as expected.

Math

import math will give you a range of handy mathematical functions.

>>> dir(math)
['__name__', 'e', 'pi', 'sqrt', 'pow', 'exp', 'log', 'cos', 'sin', 'tan', 'acos', 'asin', 'atan', 'atan2', 'ceil', 'copysign', 'fabs', 'floor', 'fmod', 'frexp', 'ldexp', 'modf', 'isfinite', 'isinf', 'isnan', 'trunc', 'radians', 'degrees']

CircuitPython supports 30-bit wide floating point values so you can use int and float whenever you expect.

Tuples, Lists, Arrays, and Dictionaries

You can organize data in ()[], and {} including strings, objects, floats, etc.

Classes, Objects and Functions

We use objects and functions extensively in our libraries so check out one of our many examples like this MCP9808 library for class examples.

Lambdas

Yep! You can create function-functions with lambda just the way you like em:

>>> g = lambda x: x**2
>>> g(8)
64

Random Numbers

To obtain random numbers:

import random

random.random() will give a floating point number from 0 to 1.0.

random.randint(min, max) will give you an integer number between min and max.

The first part of interfacing with hardware is being able to manage digital inputs and outputs. With CircuitPython, it's super easy!

This example shows how to use both a digital input and output. You can use a switch input with pullup resistor (built in) to control a digital output - the built in red LED.

Copy and paste the code into code.py using your favorite editor, and save the file to run the demo.

# CircuitPython IO demo #1 - General Purpose I/O
import time
import board
from digitalio import DigitalInOut, Direction, Pull

led = DigitalInOut(board.D13)
led.direction = Direction.OUTPUT

# For Gemma M0, Trinket M0, Metro M0 Express, ItsyBitsy M0 Express, Itsy M4 Express
switch = DigitalInOut(board.D2)
# switch = DigitalInOut(board.D5)  # For Feather M0 Express, Feather M4 Express
# switch = DigitalInOut(board.D7)  # For Circuit Playground Express
switch.direction = Direction.INPUT
switch.pull = Pull.UP

while True:
    # We could also do "led.value = not switch.value"!
    if switch.value:
        led.value = False
    else:
        led.value = True

    time.sleep(0.01)  # debounce delay

Note that we made the code a little less "Pythonic" than necessary. The if/else block could be replaced with a simple led.value = not switch.value but we wanted to make it super clear how to test the inputs. The interpreter will read the digital input when it evaluates switch.value.

For Gemma M0, Trinket M0, Metro M0 Express, Metro M4 Express, ItsyBitsy M0 Express, ItsyBitsy M4 Express, no changes to the initial example are needed.

Note: To "comment out" a line, put a # and a space before it. To "uncomment" a line, remove the # + space from the beginning of the line.

For Feather M0 Express and Feather M4 Express, comment out switch = DigitalInOut(board.D2) (and/or switch = DigitalInOut(board.D7) depending on what changes you already made), and uncomment switch = DigitalInOut(board.D5).

For Circuit Playground Express, you'll need to comment out switch = DigitalInOut(board.D2) (and/or switch = DigitalInOut(board.D5) depending on what changes you already made), and uncomment switch = DigitalInOut(board.D7).

To find the pin or pad suggested in the code, see the list below. For the boards that require wiring, wire up a switch (also known as a tactile switch, button or push-button), following the diagram for guidance. Press or slide the switch, and the onboard red LED will turn on and off.

Note that on the M0/SAMD based CircuitPython boards, at least, you can also have internal pulldowns with Pull.DOWN and if you want to turn off the pullup/pulldown just assign switch.pull = None.

Find the pins!

The list below shows each board, explains the location of the Digital pin suggested for use as input, and the location of the D13 LED.

Circuit Playground Express

 

We're going to use the switch, which is pin D7, and is located between the battery connector and the reset switch on the board. D13 is labeled D13 and is located next to the USB micro port.

 

To use D7, comment out the current pin setup line, and uncomment the line labeled for Circuit Playground Express. See the details above!

Trinket M0

 

D2 is connected to the blue wire, labeled "2", and located between "3V" and "1" on the board. D13 is labeled "13" and is located next to the USB micro port.

Gemma M0

 

D2 is an alligator-clip-friendly pad labeled both "D2" and "A1", shown connected to the blue wire, and is next to the USB micro port. D13 is located next to the "GND" label on the board, above the "On/Off" switch.

 

Use alligator clips to connect your switch to your Gemma M0!

Feather M0 Express and Feather M4 Express

 

D5 is labeled "5" and connected to the blue wire on the board. D13 is labeled "#13" and is located next to the USB micro port.

 

To use D5, comment out the current pin setup line, and uncomment the line labeled for Feather M0 Express. See the details above!

ItsyBitsy M0 Express and ItsyBitsy M4 Express

 

D2 is labeled "2", located between the "MISO" and "EN" labels, and is connected to the blue wire on the board. D13 is located next to the reset button between the "3" and "4" labels on the board.

Metro M0 Express and Metro M4 Express

 

D2 is located near the top left corner, and is connected to the blue wire. D13 is labeled "L" and is located next to the USB micro port.

Read the Docs

For a more in-depth look at what digitalio can do, check out the DigitalInOut page in Read the Docs.

This example shows you how you can read the analog voltage on the A1 pin on your board.

Copy and paste the code into code.py using your favorite editor, and save the file to run the demo.

# CircuitPython AnalogIn Demo
import time
import board
from analogio import AnalogIn

analog_in = AnalogIn(board.A1)


def get_voltage(pin):
    return (pin.value * 3.3) / 65536


while True:
    print((get_voltage(analog_in),))
    time.sleep(0.1)
Make sure you're running the latest CircuitPython! If you are not, you may run into an error: "AttributeError: 'module' object has no attribute 'A1'". If you receive this error, first make sure you're running the latest version of CircuitPython!

Creating the analog input

analog1in = AnalogIn(board.A1)

Creates an object and connects the object to A1 as an analog input.

get_voltage Helper

getVoltage(pin) is our little helper program. By default, analog readings will range from 0 (minimum) to 65535 (maximum). This helper will convert the 0-65535 reading from pin.value and convert it a 0-3.3V voltage reading.

Main Loop

The main loop is simple. It prints out the voltage as floating point values by calling get_voltage on our analog object. Connect to the serial console to see the results.

Changing It Up

By default the pins are floating so the voltages will vary. While connected to the serial console, try touching a wire from A1 to the GND pin or 3Vo pin to see the voltage change.

You can also add a potentiometer to control the voltage changes. From the potentiometer to the board, connect the left pin to ground, the middle pin to A1, and the right pin to 3V. If you're using Mu editor, you can see the changes as you rotate the potentiometer on the plotter like in the image above! (Click the Plotter icon at the top of the window to open the plotter.)

When you turn the knob of the potentiometer, the wiper rotates left and right, increasing or decreasing the resistance. This, in turn, changes the analog voltage level that will be read by your board on A1.

Wire it up

The list below shows wiring diagrams to help find the correct pins and wire up the potentiometer, and provides more information about analog pins on your board!

Circuit Playground Express

 

A1 is located on the right side of the board. There are multiple ground and 3V pads (pins).

 

Your board has 7 analog pins that can be used for this purpose. For the full list, see the pinout page on the main guide.

Trinket M0

 

A1 is labeled as 2! It's located between "1~" and "3V" on the same side of the board as the little red LED. Ground is located on the opposite side of the board. 3V is located next to 2, on the same end of the board as the reset button.

 

You have 5 analog pins you can use. For the full list, see the pinouts page on the main guide.

Gemma M0

 

A1 is located near the top of the board of the board to the left side of the USB Micro port. Ground is on the other side of the USB port from A1. 3V is located to the left side of the battery connector on the bottom of the board.

 

Your board has 3 analog pins. For the full list, see the pinout page on the main guide.

Feather M0 Express and Feather M4 Express

 

A1 is located along the edge opposite the battery connector. There are multiple ground pins. 3V is located along the same edge as A1, and is next to the reset button.

 

Your board has 6 analog pins you can use. For the full list, see the pinouts page on the main guide.

ItsyBitsy M0 Express and ItsyBitsy M4 Express

 

A1 is located in the middle of the board, near the "A" in "Adafruit". Ground is labled "G" and is located next to "BAT", near the USB Micro port. 3V is found on the opposite side of the USB port from Ground, next to RST.

 

You have 6 analog pins you can use. For a full list, see the pinouts page on the main guide.

Metro M0 Express and Metro M4 Express

 

A1 is located on the same side of the board as the barrel jack. There are multiple ground pins available. 3V is labeled "3.3" and is located in the center of the board on the same side as the barrel jack (and as A1).

 

Your Metro M0 Express board has 6 analog pins you can use. For the full list, see the pinouts page on the main guide.

 

Your Metro M4 Express board has 6 analog pins you can use. For the full list, see the pinouts page on the main guide.

Reading Analog Pin Values

The get_voltage() helper used in the potentiometer example above reads the raw analog pin value and converts it to a voltage level. You can, however, directly read an analog pin value in your code by using pin.value. For example, to simply read the raw analog pin value from the potentiometer, you would run the following code:

Download: file
import time
import board
from analogio import AnalogIn

analog_in = AnalogIn(board.A1)

while True:
    print(analog_in.value)
    time.sleep(0.1)

This works with any analog pin or input. Use the <pin_name>.value to read the raw value and utilise it in your code.

This example shows you how you can set the DAC (true analog output) on pin A0.

A0 is the only true analog output on the M0 boards. No other pins do true analog output!

Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython IO demo - analog output
import board
from analogio import AnalogOut

analog_out = AnalogOut(board.A0)

while True:
    # Count up from 0 to 65535, with 64 increment
    # which ends up corresponding to the DAC's 10-bit range
    for i in range(0, 65535, 64):
        analog_out.value = i

Creating an analog output

analog_out = AnalogOut(A0)

Creates an object analog_out and connects the object to A0, the only DAC pin available on both the M0 and the M4 boards. (The M4 has two, A0 and A1.)

Setting the analog output

The DAC on the SAMD21 is a 10-bit output, from 0-3.3V. So in theory you will have a resolution of 0.0032 Volts per bit. To allow CircuitPython to be general-purpose enough that it can be used with chips with anything from 8 to 16-bit DACs, the DAC takes a 16-bit value and divides it down internally.

For example, writing 0 will be the same as setting it to 0 - 0 Volts out.

Writing 5000 is the same as setting it to 5000 / 64 = 78, and 78 / 1024 * 3.3V = 0.25V output.

Writing 65535 is the same as 1023 which is the top range and you'll get 3.3V output

Main Loop

The main loop is fairly simple, it goes through the entire range of the DAC, from 0 to 65535, but increments 64 at a time so it ends up clicking up one bit for each of the 10-bits of range available.

CircuitPython is not terribly fast, so at the fastest update loop you'll get 4 Hz. The DAC isn't good for audio outputs as-is.

Express boards like the Circuit Playground Express, Metro M0 Express, ItsyBitsy M0 Express, ItsyBitsy M4 Express, Metro M4 Express, Feather M4 Express, or Feather M0 Express have more code space and can perform audio playback capabilities via the DAC. Gemma M0 and Trinket M0 cannot!

Check out the Audio Out section of this guide for examples!

Find the pin

Use the diagrams below to find the A0 pin marked with a magenta arrow!

Circuit Playground Express

 

A0 is located between VOUT and A1 near the battery port.

Trinket M0

 

A0 is labeled "1~" on Trinket! A0 is located between "0" and "2" towards the middle of the board on the same side as the red LED.

Gemma M0

 

A0 is located in the middle of the right side of the board next to the On/Off switch.

Feather M0 Express

 

A0 is located between GND and A1 on the opposite side of the board from the battery connector, towards the end with the Reset button.

Feather M4 Express

 

A0 is located between GND and A1 on the opposite side of the board from the battery connector, towards the end with the Reset button, and the pin pad has left and right white parenthesis markings around it

ItsyBitsy M0 Express

 

A0 is located between VHI and A1, near the "A" in "Adafruit", and the pin pad has left and right white parenthesis markings around it.

ItsyBitsy M4 Express

 

A0 is located between VHI and A1, and the pin pad has left and right white parenthesis markings around it.

Metro M0 Express

 

A0 is between VIN and A1, and is located along the same side of the board as the barrel jack adapter towards the middle of the headers found on that side of the board.

Metro M4 Express

 

A0 is between VIN and A1, and is located along the same side of the board as the barrel jack adapter towards the middle of the headers found on that side of the board.

 

On the Metro M4 Express, there are TWO true analog outputs: A0 and A1.

Your board has pulseio support, which means you can PWM LEDs, control servos, beep piezos, and manage "pulse train" type devices like DHT22 and Infrared.

Nearly every pin has PWM support! For example, all ATSAMD21 board have an A0 pin which is 'true' analog out and does not have PWM support.

PWM with Fixed Frequency

This example will show you how to use PWM to fade the little red LED on your board.

Copy and paste the code into code.py using your favorite editor, and save the file.

import time
import board
import pulseio

led = pulseio.PWMOut(board.D13, frequency=5000, duty_cycle=0)

while True:
    for i in range(100):
        # PWM LED up and down
        if i < 50:
            led.duty_cycle = int(i * 2 * 65535 / 100)  # Up
        else:
            led.duty_cycle = 65535 - int((i - 50) * 2 * 65535 / 100)  # Down
        time.sleep(0.01)

Create a PWM Output

led = pulseio.PWMOut(board.D13, frequency=5000, duty_cycle=0)

Since we're using the onboard LED, we'll call the object led, use pulseio.PWMOut to create the output and pass in the D13 LED pin to use.

Main Loop

The main loop uses range() to cycle through the loop. When the range is below 50, it PWMs the LED brightness up, and when the range is above 50, it PWMs the brightness down. This is how it fades the LED brighter and dimmer!

The time.sleep() is needed to allow the PWM process to occur over a period of time. Otherwise it happens too quickly for you to see!

PWM Output with Variable Frequency

Fixed frequency outputs are great for pulsing LEDs or controlling servos. But if you want to make some beeps with a piezo, you'll need to vary the frequency.

The following example uses pulseio to make a series of tones on a piezo.

To use with any of the M0 boards, no changes to the following code are needed.

To use with the Metro M4 Express, ItsyBitsy M4 Express or the Feather M4 Express, you must comment out the piezo = pulseio.PWMOut(board.A2, duty_cycle=0, frequency=440, variable_frequency=True) line and uncomment the piezo = pulseio.PWMOut(board.A1, duty_cycle=0, frequency=440, variable_frequency=True) line. A2 is not a supported PWM pin on the M4 boards!

Remember: To "comment out" a line, put a # and a space before it. To "uncomment" a line, remove the # + space from the beginning of the line.
import time
import board
import pulseio

# For the M0 boards:
piezo = pulseio.PWMOut(board.A2, duty_cycle=0, frequency=440, variable_frequency=True)

# For the M4 boards:
# piezo = pulseio.PWMOut(board.A1, duty_cycle=0, frequency=440, variable_frequency=True)

while True:
    for f in (262, 294, 330, 349, 392, 440, 494, 523):
        piezo.frequency = f
        piezo.duty_cycle = 65535 // 2  # On 50%
        time.sleep(0.25)  # On for 1/4 second
        piezo.duty_cycle = 0  # Off
        time.sleep(0.05)  # Pause between notes
    time.sleep(0.5)

If you have simpleio library loaded into your /lib folder on your board, we have a nice little helper that makes a tone for you on a piezo with a single command.

To use with any of the M0 boards, no changes to the following code are needed.

To use with the Metro M4 Express, ItsyBitsy M4 Express or the Feather M4 Express, you must comment out the simpleio.tone(board.A2, f, 0.25) line and uncomment the simpleio.tone(board.A1, f, 0.25) line. A2 is not a supported PWM pin on the M4 boards!

import time
import board
import simpleio

while True:
    for f in (262, 294, 330, 349, 392, 440, 494, 523):
        # For the M0 boards:
        simpleio.tone(board.A2, f, 0.25)  # on for 1/4 second
        # For the M4 boards:
        # simpleio.tone(board.A1, f, 0.25)  # on for 1/4 second
        time.sleep(0.05)  # pause between notes
    time.sleep(0.5)

As you can see, it's much simpler!

Wire it up

Use the diagrams below to help you wire up your piezo. Attach one leg of the piezo to pin A2 on the M0 boards or A1 on the M4 boards, and the other leg to ground. It doesn't matter which leg is connected to which pin. They're interchangeable!

Circuit Playground Express

 

Use alligator clips to attach A2 and any one of the GND to different legs of the piezo.

 

CPX has PWM on the following pins: A1, A2, A3, A6, RX, LIGHT, A8, TEMPERATURE, A9, BUTTON_B, D5, SLIDE_SWITCH, D7, D13, REMOTEIN, IR_RX, REMOTEOUT, IR_TX, IR_PROXIMITY, MICROPHONE_CLOCK, MICROPHONE_DATA, ACCELEROMETER_INTERRUPT, ACCELEROMETER_SDA, ACCELEROMETER_SCL, SPEAKER_ENABLE.

 

There is NO PWM on: A0, SPEAKER, A4, SCL, A5, SDA, A7, TX, BUTTON_A, D4, NEOPIXEL, D8, SCK, MOSI, MISO, FLASH_CS.

Trinket M0

 

Note: A2 on Trinket is also labeled Digital "0"!

 

Use jumper wires to connect GND and D0 to different legs of the piezo.

 

Trinket has PWM available on the following pins: D0, A2, SDA, D2, A1, SCL, MISO, D4, A4, TX, MOSI, D3, A3, RX, SCK, D13, APA102_MOSI, APA102_SCK.

 

There is NO PWM on: A0, D1.

Gemma M0

 

Use alligator clips to attach A2 and GND to different legs on the piezo.

 

Gemma has PWM available on the following pins: A1, D2, RX, SCL, A2, D0, TX, SDA, L, D13, APA102_MOSI, APA102_SCK.

 

There is NO PWM on: A0, D1.

Feather M0 Express

 

Use jumper wires to attach A2 and one of the two GND to different legs of the piezo.

 

Feather M0 Express has PWM on the following pins: A2, A3, A4, SCK, MOSI, MISO, D0, RX, D1, TX, SDA, SCL, D5, D6, D9, D10, D11, D12, D13, NEOPIXEL.

 

There is NO PWM on: A0, A1, A5.

Feather M4 Express

 

Use jumper wires to attach A1 and one of the two GND to different legs of the piezo.

 

To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!

 

Feather M4 Express has PWM on the following pins: A1, A3, SCK, D0, RX, D1, TX, SDA, SCL, D4, D5, D6, D9, D10, D11, D12, D13.

 

There is NO PWM on: A0, A2, A4, A5, MOSI, MISO.

ItsyBitsy M0 Express

 

Use jumper wires to attach A2 and G to different legs of the piezo.

 

ItsyBitsy M0 Express has PWM on the following pins: D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, L, A2, A3, A4, MOSI, MISO, SCK, SCL, SDA, APA102_MOSI, APA102_SCK.

 

There is NO PWM on: A0, A1, A5.

ItsyBitsy M4 Express

 

Use jumper wires to attach A1 and G to different legs of the piezo.

 

To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!

 

ItsyBitsy M4 Express has PWM on the following pins: A1, D0, RX, D1, TX, D2, D4, D5, D7, D9, D10, D11, D12, D13, SDA, SCL.

There is NO PWM on: A2, A3, A4, A5, D3, SCK, MOSI, MISO.

Metro M0 Express

 

Use jumper wires to connect A2 and any one of the GND to different legs on the piezo.

 

Metro M0 Express has PWM on the following pins: A2, A3, A4, D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, SDA, SCL, NEOPIXEL, SCK, MOSI, MISO.

 

There is NO PWM on: A0, A1, A5, FLASH_CS.

Metro M4 Express

 

Use jumper wires to connect A1 and any one of the GND to different legs on the piezo.

 

To use A1, comment out the current pin setup line, and uncomment the line labeled for the M4 boards. See the details above!


Metro M4 Express has PWM on: A1, A5, D0, RX, D1, TX, D2, D3, D4, D5, D6, D7, D8, D9, D10, D11, D12, D13, SDA, SCK, MOSI, MISO

 

There is No PWM on: A0, A2, A3, A4, SCL, AREF, NEOPIXEL, LED_RX, LED_TX.

Where's My PWM?

Want to check to see which pins have PWM yourself? We've written this handy script! It attempts to setup PWM on every pin available, and lets you know which ones work and which ones don't. Check it out!

import board
import pulseio

for pin_name in dir(board):
    pin = getattr(board, pin_name)
    try:
        p = pulseio.PWMOut(pin)
        p.deinit()
        print("PWM on:", pin_name)  # Prints the valid, PWM-capable pins!
    except ValueError:  # This is the error returned when the pin is invalid.
        print("No PWM on:", pin_name)  # Prints the invalid pins.
    except RuntimeError:  # Timer conflict error.
        print("Timers in use:", pin_name)  # Prints the timer conflict pins.
    except TypeError:  # Error returned when checking a non-pin object in dir(board).
        pass  # Passes over non-pin objects in dir(board).

In order to use servos, we take advantage of pulseio. Now, in theory, you could just use the raw pulseio calls to set the frequency to 50 Hz and then set the pulse widths. But we would rather make it a little more elegant and easy!

So, instead we will use adafruit_motor which manages servos for you quite nicely! adafruit_motor is a library so be sure to grab it from the library bundle if you have not yet! If you need help installing the library, check out the CircuitPython Libraries page.

Servos come in two types: 

  • A standard hobby servo - the horn moves 180 degrees (90 degrees in each direction from zero degrees).
  • A continuous servo - the horn moves in full rotation like a DC motor. Instead of an angle specified, you set a throttle value with 1.0 being full forward, 0.5 being half forward, 0 being stopped, and -1 being full reverse, with other values between.

Servo Wiring

Servos will only work on PWM-capable pins! Check your board details to verify which pins have PWM outputs.

The connections for a servo are the same for standard servos and continuous rotation servos.

Connect the servo's brown or black ground wire to ground on the CircuitPython board.

Connect the servo's red power wire to 5V power, USB power is good for a servo or two. For more than that, you'll need an external battery pack. Do not use 3.3V for powering a servo!

Connect the servo's yellow or white signal wire to the control/data pin, in this case A1 or A2 but you can use any PWM-capable pin.

For example, to wire a servo to Trinket, connect the ground wire to GND, the power wire to USB, and the signal wire to 0.

 

Remember, A2 on Trinket is labeled "0".

 

 

For Gemma, use jumper wire alligator clips to connect the ground wire to GND, the power wire to VOUT, and the signal wire to A2.

For Circuit Playground Express and Circuit Playground Bluefruit, use jumper wire alligator clips to connect the ground wire to GND, the power wire to VOUT, and the signal wire to A2.

For boards like Feather M0 Express, ItsyBitsy M0 Express and Metro M0 Express, connect the ground wire to any GND, the power wire to USB or 5V, and the signal wire to A2.

For the Metro M4 Express, ItsyBitsy M4 Express and the Feather M4 Express, connect the ground wire to any G or GND, the power wire to USB or 5V, and the signal wire to A1.

Standard Servo Code

Here's an example that will sweep a servo connected to pin A2 from 0 degrees to 180 degrees (-90 to 90 degrees) and back:

import time
import board
import pulseio
from adafruit_motor import servo

# create a PWMOut object on Pin A2.
pwm = pulseio.PWMOut(board.A2, duty_cycle=2 ** 15, frequency=50)

# Create a servo object, my_servo.
my_servo = servo.Servo(pwm)

while True:
    for angle in range(0, 180, 5):  # 0 - 180 degrees, 5 degrees at a time.
        my_servo.angle = angle
        time.sleep(0.05)
    for angle in range(180, 0, -5): # 180 - 0 degrees, 5 degrees at a time.
        my_servo.angle = angle
        time.sleep(0.05)

Continuous Servo Code

There are two differences with Continuous Servos vs. Standard Servos:

  1. The servo object is created like my_servo = servo.ContinuousServo(pwm) instead of my_servo = servo.Servo(pwm)
  2. Instead of using myservo.angle, you use my_servo.throttle using a throttle value from 1.0 (full on) to 0.0 (stopped) to -1.0 (full reverse). Any number between would be a partial speed forward (positive) or reverse (negative). This is very similar to standard DC motor control with the adafruit_motor library.

This example runs full forward for 2 seconds, stops for 2 seconds, runs full reverse for 2 seconds, then stops for 4 seconds.

# Continuous Servo Test Program for CircuitPython
import time
import board
import pulseio
from adafruit_motor import servo

# create a PWMOut object on Pin A2.
pwm = pulseio.PWMOut(board.A2, frequency=50)

# Create a servo object, my_servo.
my_servo = servo.ContinuousServo(pwm)

while True:
    print("forward")
    my_servo.throttle = 1.0
    time.sleep(2.0)
    print("stop")
    my_servo.throttle = 0.0
    time.sleep(2.0)
    print("reverse")
    my_servo.throttle = -1.0
    time.sleep(2.0)
    print("stop")
    my_servo.throttle = 0.0
    time.sleep(4.0)

Pretty simple!

Note that we assume that 0 degrees is 0.5ms and 180 degrees is a pulse width of 2.5ms. That's a bit wider than the official 1-2ms pulse widths. If you have a servo that has a different range you can initialize the servo object with a different min_pulse and max_pulse. For example:

my_servo = servo.Servo(pwm, min_pulse = 500, max_pulse = 2500) 

For more detailed information on using servos with CircuitPython, check out the CircuitPython section of the servo guide!

Every board has a built in RGB LED. You can use CircuitPython to control the color and brightness of this LED. There are two different types of internal RGB LEDs: DotStar and NeoPixel. This section covers both and explains which boards have which LED.

circuitpython_NeoPixelDotStar.jpg
NeoPixel on the left, DotStar on the right. Not to scale... onboard DotStars are tiny!

The first example will show you how to change the color and brightness of the internal RGB LED.

Copy and paste the code into code.py using your favorite editor, and save the file.

import time
import board

# For Trinket M0, Gemma M0, ItsyBitsy M0 Express, and ItsyBitsy M4 Express
import adafruit_dotstar
led = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1)
# For Feather M0 Express, Metro M0 Express, Metro M4 Express, and Circuit Playground Express
# import neopixel
# led = neopixel.NeoPixel(board.NEOPIXEL, 1)

led.brightness = 0.3

while True:
    led[0] = (255, 0, 0)
    time.sleep(0.5)
    led[0] = (0, 255, 0)
    time.sleep(0.5)
    led[0] = (0, 0, 255)
    time.sleep(0.5)

Create the LED

First, we create the LED object and attach it to the correct pin or pins. In the case of a NeoPixel, there is only one pin necessary, and we have called it NEOPIXEL for easier use. In the case of a DotStar, however, there are two pins necessary, and so we use the pin names APA102_MOSI and APA102_SCK to get it set up. Since we're using the single onboard LED, the last thing we do is tell it that there's only 1 LED!

Trinket M0, Gemma M0, ItsyBitsy M0 Express, and ItsyBitsy M4 Express each have an onboard Dotstar LED, so no changes are needed to the initial version of the example.

Feather M0 Express, Feather M4 Express, Metro M0 Express, Metro M4 Express, and Circuit Playground Express each have an onboard NeoPixel LED, so you must comment out import adafruit_dotstar and led = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1), and uncomment import neopixel and led = neopixel.NeoPixel(board.NEOPIXEL, 1).

Remember: To "comment out" a line, put a # and a space before it. To "uncomment" a line, remove the # + space from the beginning of the line.

Brightness

To set the brightness you simply use the brightness attribute. Brightness is set with a number between 0 and 1, representative of a percent from 0% to 100%. So, led.brightness = (0.3) sets the LED brightness to 30%. The default brightness is 1 or 100%, and at it's maximum, the LED is blindingly bright! You can set it lower if you choose.

Main Loop

LED colors are set using a combination of red, green, and blue, in the form of an (RG, B) tuple. Each member of the tuple is set to a number between 0 and 255 that determines the amount of each color present. Red, green and blue in different combinations can create all the colors in the rainbow! So, for example, to set the LED to red, the tuple would be (255, 0, 0), which has the maximum level of red, and no green or blue. Green would be (0, 255, 0), etc. For the colors between, you set a combination, such as cyan which is (0, 255, 255), with equal amounts of green and blue.

The main loop is quite simple. It sets the first LED to red using (255, 0, 0), then green using (0, 255, 0), and finally blue using (0, 0, 255). Next, we give it a time.sleep() so it stays each color for a period of time. We chose time.sleep(0.5), or half a second. Without the time.sleep() it'll flash really quickly and the colors will be difficult to see!

Note that we set led[0]. This means the first, and in the case of most of the boards, the only LED. In CircuitPython, counting starts at 0. So the first of any object, list, etc will be 0!

Try changing the numbers in the tuples to change your LED to any color of the rainbow. Or, you can add more lines with different color tuples to add more colors to the sequence. Always add the time.sleep(), but try changing the amount of time to create different cycle animations!

Making Rainbows (Because Who Doesn't Love 'Em!)

Coding a rainbow effect involves a little math and a helper function called wheel. For details about how wheel works, see this explanation here!

The last example shows how to do a rainbow animation on the internal RGB LED.

Copy and paste the code into code.py using your favorite editor, and save the file. Remember to comment and uncomment the right lines for the board you're using, as explained above.

import time
import board

# For Trinket M0, Gemma M0, ItsyBitsy M0 Express and ItsyBitsy M4 Express
import adafruit_dotstar
led = adafruit_dotstar.DotStar(board.APA102_SCK, board.APA102_MOSI, 1)
# For Feather M0 Express, Metro M0 Express, Metro M4 Express and Circuit Playground Express
# import neopixel
# led = neopixel.NeoPixel(board.NEOPIXEL, 1)


def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return 0, 0, 0
    if pos < 85:
        return int(255 - pos * 3), int(pos * 3), 0
    if pos < 170:
        pos -= 85
        return 0, int(255 - pos * 3), int(pos * 3)
    pos -= 170
    return int(pos * 3), 0, int(255 - (pos * 3))


led.brightness = 0.3

i = 0
while True:
    i = (i + 1) % 256  # run from 0 to 255
    led.fill(wheel(i))
    time.sleep(0.1)

We add the wheel function in after setup but before our main loop.

And right before our main loop, we assign the variable i = 0, so it's ready for use inside the loop.

The main loop contains some math that cycles i from 0 to 255 and around again repeatedly. We use this value to cycle wheel() through the rainbow!

The time.sleep() determines the speed at which the rainbow changes. Try a higher number for a slower rainbow or a lower number for a faster one!

Circuit Playground Express Rainbow

Note that here we use led.fill instead of led[0]. This means it turns on all the LEDs, which in the current code is only one. So why bother with fill? Well, you may have a Circuit Playground Express, which as you can see has TEN NeoPixel LEDs built in. The examples so far have only turned on the first one. If you'd like to do a rainbow on all ten LEDs, change the 1 in:

led = neopixel.NeoPixel(board.NEOPIXEL, 1)

to 10 so it reads:

led = neopixel.NeoPixel(board.NEOPIXEL, 10).

This tells the code to look for 10 LEDs instead of only 1. Now save the code and watch the rainbow go! You can make the same 1 to 10 change to the previous examples as well, and use led.fill to light up all the LEDs in the colors you chose! For more details, check out the NeoPixel section of the CPX guide!

NeoPixels are a revolutionary and ultra-popular way to add lights and color to your project. These stranded RGB lights have the controller inside the LED, so you just push the RGB data and the LEDs do all the work for you. They're a perfect match for CircuitPython!

You can drive 300 NeoPixel LEDs with brightness control (set brightness=1.0 in object creation) and 1000 LEDs without. That's because to adjust the brightness we have to dynamically recreate the data-stream each write.

You'll need the neopixel.mpy library if you don't already have it in your /lib folder! You can get it from the CircuitPython Library Bundle. If you need help installing the library, check out the CircuitPython Libraries page.

Wiring It Up

You'll need to solder up your NeoPixels first. Verify your connection is on the DATA INPUT or DIN side. Plugging into the DATA OUT or DOUT side is a common mistake! The connections are labeled and some formats have arrows to indicate the direction the data must flow.

For powering the pixels from the board, the 3.3V regulator output can handle about 500mA peak which is about 50 pixels with 'average' use. If you want really bright lights and a lot of pixels, we recommend powering direct from an external power source.

  • On Gemma M0 and Circuit Playground Express this is the Vout pad - that pad has direct power from USB or the battery, depending on which is higher voltage.
  • On Trinket M0, Feather M0 Express, Feather M4 Express, ItsyBitsy M0 Express and ItsyBitsy M4 Express the USB or BAT pins will give you direct power from the USB port or battery.
  • On Metro M0 Express and Metro M4 Express, use the 5V pin regardless of whether it's powered via USB or the DC jack.

If the power to the NeoPixels is greater than 5.5V you may have some difficulty driving some strips, in which case you may need to lower the voltage to 4.5-5V or use a level shifter.

Do not use the VIN pin directly on Metro M0 Express or Metro M4 Express! The voltage can reach 9V and this can destroy your NeoPixels!
Note that the wire ordering on your NeoPixel strip or shape may not exactly match the diagram above. Check the markings to verify which pin is DIN, 5V and GND

The Code

This example includes multiple visual effects. Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython demo - NeoPixel
import time
import board
import neopixel

pixel_pin = board.A1
num_pixels = 8

pixels = neopixel.NeoPixel(pixel_pin, num_pixels, brightness=0.3, auto_write=False)


def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)


def color_chase(color, wait):
    for i in range(num_pixels):
        pixels[i] = color
        time.sleep(wait)
        pixels.show()
    time.sleep(0.5)


def rainbow_cycle(wait):
    for j in range(255):
        for i in range(num_pixels):
            rc_index = (i * 256 // num_pixels) + j
            pixels[i] = wheel(rc_index & 255)
        pixels.show()
        time.sleep(wait)


RED = (255, 0, 0)
YELLOW = (255, 150, 0)
GREEN = (0, 255, 0)
CYAN = (0, 255, 255)
BLUE = (0, 0, 255)
PURPLE = (180, 0, 255)

while True:
    pixels.fill(RED)
    pixels.show()
    # Increase or decrease to change the speed of the solid color change.
    time.sleep(1)
    pixels.fill(GREEN)
    pixels.show()
    time.sleep(1)
    pixels.fill(BLUE)
    pixels.show()
    time.sleep(1)

    color_chase(RED, 0.1)  # Increase the number to slow down the color chase
    color_chase(YELLOW, 0.1)
    color_chase(GREEN, 0.1)
    color_chase(CYAN, 0.1)
    color_chase(BLUE, 0.1)
    color_chase(PURPLE, 0.1)

    rainbow_cycle(0)  # Increase the number to slow down the rainbow

Create the LED

The first thing we'll do is create the LED object. The NeoPixel object has two required arguments and two optional arguments. You are required to set the pin you're using to drive your NeoPixels and provide the number of pixels you intend to use. You can optionally set brightness and auto_write.

NeoPixels can be driven by any pin. We've chosen A1. To set the pin, assign the variable pixel_pin to the pin you'd like to use, in our case board.A1.

To provide the number of pixels, assign the variable num_pixels to the number of pixels you'd like to use. In this example, we're using a strip of 8.

We've chosen to set brightness=0.3, or 30%.

By default, auto_write=True, meaning any changes you make to your pixels will be sent automatically. Since True is the default, if you use that setting, you don't need to include it in your LED object at all. We've chosen to set auto_write=False. If you set auto_write=False, you must include pixels.show() each time you'd like to send data to your pixels. This makes your code more complicated, but it can make your LED animations faster!

NeoPixel Helpers

Next we've included a few helper functions to create the super fun visual effects found in this code. First is wheel() which we just learned with the Internal RGB LED. Then we have color_chase() which requires you to provide a color and the amount of time in seconds you'd like between each step of the chase. Next we have rainbow_cycle(), which requires you to provide the mount of time in seconds you'd like the animation to take. Last, we've included a list of variables for our colors. This makes it much easier if to reuse the colors anywhere in the code, as well as add more colors for use in multiple places. Assigning and using RGB colors is explained in this section of the CircuitPython Internal RGB LED page.

Main Loop

Thanks to our helpers, our main loop is quite simple. We include the code to set every NeoPixel we're using to red, green and blue for 1 second each. Then we call color_chase(), one time for each color on our list with 0.1 second delay between setting each subsequent LED the same color during the chase. Last we call rainbow_cycle(0), which means the animation is as fast as it can be. Increase both of those numbers to slow down each animation!

Note that the longer your strip of LEDs, the longer it will take for the animations to complete.

We have a ton more information on general purpose NeoPixel know-how at our NeoPixel UberGuide https://learn.adafruit.com/adafruit-neopixel-uberguide

NeoPixel RGBW

NeoPixels are available in RGB, meaning there are three LEDs inside, red, green and blue. They're also available in RGBW, which includes four LEDs, red, green, blue and white. The code for RGBW NeoPixels is a little bit different than RGB.

If you run RGB code on RGBW NeoPixels, approximately 3/4 of the LEDs will light up and the LEDs will be the incorrect color even though they may appear to be changing. This is because NeoPixels require a piece of information for each available color (red, green, blue and possibly white).

Therefore, RGB LEDs require three pieces of information and RGBW LEDs require FOUR pieces of information to work. So when you create the LED object for RGBW LEDs, you'll include bpp=4, which sets bits-per-pixel to four (the four pieces of information!).

Then, you must include an extra number in every color tuple you create. For example, red will be (255, 0, 0, 0). This is how you send the fourth piece of information. Check out the example below to see how our NeoPixel code looks for using with RGBW LEDs!

# CircuitPython demo - NeoPixel RGBW

import time
import board
import neopixel

pixel_pin = board.A1
num_pixels = 8

pixels = neopixel.NeoPixel(pixel_pin, num_pixels, brightness=0.3, auto_write=False,
                           pixel_order=(1, 0, 2, 3))


def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3, 0)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3, 0)


def color_chase(color, wait):
    for i in range(num_pixels):
        pixels[i] = color
        time.sleep(wait)
        pixels.show()
    time.sleep(0.5)


def rainbow_cycle(wait):
    for j in range(255):
        for i in range(num_pixels):
            rc_index = (i * 256 // num_pixels) + j
            pixels[i] = wheel(rc_index & 255)
        pixels.show()
        time.sleep(wait)


RED = (255, 0, 0, 0)
YELLOW = (255, 150, 0, 0)
GREEN = (0, 255, 0, 0)
CYAN = (0, 255, 255, 0)
BLUE = (0, 0, 255, 0)
PURPLE = (180, 0, 255, 0)

while True:
    pixels.fill(RED)
    pixels.show()
    # Increase or decrease to change the speed of the solid color change.
    time.sleep(1)
    pixels.fill(GREEN)
    pixels.show()
    time.sleep(1)
    pixels.fill(BLUE)
    pixels.show()
    time.sleep(1)

    color_chase(RED, 0.1)  # Increase the number to slow down the color chase
    color_chase(YELLOW, 0.1)
    color_chase(GREEN, 0.1)
    color_chase(CYAN, 0.1)
    color_chase(BLUE, 0.1)
    color_chase(PURPLE, 0.1)

    rainbow_cycle(0)  # Increase the number to slow down the rainbow

Read the Docs

For a more in depth look at what neopixel can do, check out NeoPixel on Read the Docs.

DotStars use two wires, unlike NeoPixel's one wire. They're very similar but you can write to DotStars much faster with hardware SPI and they have a faster PWM cycle so they are better for light painting.

Any pins can be used but if the two pins can form a hardware SPI port, the library will automatically switch over to hardware SPI. If you use hardware SPI then you'll get 4 MHz clock rate (that would mean updating a 64 pixel strand in about 500uS - that's 0.0005 seconds). If you use non-hardware SPI pins you'll drop down to about 3KHz, 1000 times as slow!

You can drive 300 DotStar LEDs with brightness control (set brightness=1.0 in object creation) and 1000 LEDs without. That's because to adjust the brightness we have to dynamically recreate the data-stream each write.

You'll need the adafruit_dotstar.mpy library if you don't already have it in your /lib folder! You can get it from the CircuitPython Library Bundle. If you need help installing the library, check out the CircuitPython Libraries page.

Wire It Up

You'll need to solder up your DotStars first. Verify your connection is on the DATA INPUT or DI and CLOCK INPUT or CI side. Plugging into the DATA OUT/DO or CLOCK OUT/CO side is a common mistake! The connections are labeled and some formats have arrows to indicate the direction the data must flow. Always verify your wiring with a visual inspection, as the order of the connections can differ from strip to strip!

For powering the pixels from the board, the 3.3V regulator output can handle about 500mA peak which is about 50 pixels with 'average' use. If you want really bright lights and a lot of pixels, we recommend powering direct from an external power source.

  • On Gemma M0 and Circuit Playground Express this is the Vout pad - that pad has direct power from USB or the battery, depending on which is higher voltage.
  • On Trinket M0, Feather M0 Express, Feather M4 Express, ItsyBitsy M0 Express and ItsyBitsy M4 Express the USB or BAT pins will give you direct power from the USB port or battery.
  • On Metro M0 Express and Metro M4 Express, use the 5V pin regardless of whether it's powered via USB or the DC jack.

If the power to the DotStars is greater than 5.5V you may have some difficulty driving some strips, in which case you may need to lower the voltage to 4.5-5V or use a level shifter.

Do not use the VIN pin directly on Metro M0 Express or Metro M4 Express! The voltage can reach 9V and this can destroy your DotStars!
Note that the wire ordering on your DotStar strip or shape may not exactly match the diagram above. Check the markings to verify which pin is DIN, CIN, 5V and GND

The Code

This example includes multiple visual effects. Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython demo - Dotstar
import time
import adafruit_dotstar
import board

num_pixels = 30
pixels = adafruit_dotstar.DotStar(board.A1, board.A2, num_pixels, brightness=0.1, auto_write=False)


def wheel(pos):
    # Input a value 0 to 255 to get a color value.
    # The colours are a transition r - g - b - back to r.
    if pos < 0 or pos > 255:
        return (0, 0, 0)
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)


def color_fill(color, wait):
    pixels.fill(color)
    pixels.show()
    time.sleep(wait)


def slice_alternating(wait):
    pixels[::2] = [RED] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[1::2] = [ORANGE] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[::2] = [YELLOW] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[1::2] = [GREEN] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[::2] = [TEAL] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[1::2] = [CYAN] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[::2] = [BLUE] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[1::2] = [PURPLE] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[::2] = [MAGENTA] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)
    pixels[1::2] = [WHITE] * (num_pixels // 2)
    pixels.show()
    time.sleep(wait)


def slice_rainbow(wait):
    pixels[::6] = [RED] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)
    pixels[1::6] = [ORANGE] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)
    pixels[2::6] = [YELLOW] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)
    pixels[3::6] = [GREEN] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)
    pixels[4::6] = [BLUE] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)
    pixels[5::6] = [PURPLE] * (num_pixels // 6)
    pixels.show()
    time.sleep(wait)


def rainbow_cycle(wait):
    for j in range(255):
        for i in range(num_pixels):
            rc_index = (i * 256 // num_pixels) + j
            pixels[i] = wheel(rc_index & 255)
        pixels.show()
        time.sleep(wait)


RED = (255, 0, 0)
YELLOW = (255, 150, 0)
ORANGE = (255, 40, 0)
GREEN = (0, 255, 0)
TEAL = (0, 255, 120)
CYAN = (0, 255, 255)
BLUE = (0, 0, 255)
PURPLE = (180, 0, 255)
MAGENTA = (255, 0, 20)
WHITE = (255, 255, 255)

while True:
    # Change this number to change how long it stays on each solid color.
    color_fill(RED, 0.5)
    color_fill(YELLOW, 0.5)
    color_fill(ORANGE, 0.5)
    color_fill(GREEN, 0.5)
    color_fill(TEAL, 0.5)
    color_fill(CYAN, 0.5)
    color_fill(BLUE, 0.5)
    color_fill(PURPLE, 0.5)
    color_fill(MAGENTA, 0.5)
    color_fill(WHITE, 0.5)

    # Increase or decrease this to speed up or slow down the animation.
    slice_alternating(0.1)

    color_fill(WHITE, 0.5)

    # Increase or decrease this to speed up or slow down the animation.
    slice_rainbow(0.1)

    time.sleep(0.5)

    # Increase this number to slow down the rainbow animation.
    rainbow_cycle(0)
We've chosen pins A1 and A2, but these are not SPI pins on all boards. DotStars respond faster when using hardware SPI!

Create the LED

The first thing we'll do is create the LED object. The DotStar object has three required arguments and two optional arguments. You are required to set the pin you're using for data, set the pin you'll be using for clock, and provide the number of pixels you intend to use. You can optionally set brightness and auto_write.

DotStars can be driven by any two pins. We've chosen A1 for clock and A2 for data. To set the pins, include the pin names at the beginning of the object creation, in this case board.A1 and board.A2.

To provide the number of pixels, assign the variable num_pixels to the number of pixels you'd like to use. In this example, we're using a strip of 72.

We've chosen to set brightness=0.1, or 10%.

By default, auto_write=True, meaning any changes you make to your pixels will be sent automatically. Since True is the default, if you use that setting, you don't need to include it in your LED object at all. We've chosen to set auto_write=False. If you set auto_write=False, you must include pixels.show() each time you'd like to send data to your pixels. This makes your code more complicated, but it can make your LED animations faster!

DotStar Helpers

We've included a few helper functions to create the super fun visual effects found in this code. 

First is wheel() which we just learned with the Internal RGB LED. Then we have color_fill() which requires you to provide a color and the length of time you'd like it to be displayed. Next, are slice_alternating(), slice_rainbow(), and rainbow_cycle() which require you to provide the amount of time in seconds you'd between each step of the animation.

Last, we've included a list of variables for our colors. This makes it much easier if to reuse the colors anywhere in the code, as well as add more colors for use in multiple places. Assigning and using RGB colors is explained in this section of the CircuitPython Internal RGB LED page.

The two slice helpers utilise a nifty feature of the DotStar library that allows us to use math to light up LEDs in repeating patterns. slice_alternating() first lights up the even number LEDs and then the odd number LEDs and repeats this back and forth. slice_rainbow() lights up every sixth LED with one of the six rainbow colors until the strip is filled. Both use our handy color variables. This slice code only works when the total number of LEDs is divisible by the slice size, in our case 2 and 6. DotStars come in strips of 30, 60, 72, and 144, all of which are divisible by 2 and 6. In the event that you cut them into different sized strips, the code in this example may not work without modification. However, as long as you provide a total number of LEDs that is divisible by the slices, the code will work.

Main Loop

Our main loop begins by calling color_fill() once for each color on our list and sets each to hold for 0.5 seconds. You can change this number to change how fast each color is displayed. Next, we call slice_alternating(0.1), which means there's a 0.1 second delay between each change in the animation. Then, we fill the strip white to create a clean backdrop for the rainbow to display. Then, we call slice_rainbow(0.1), for a 0.1 second delay in the animation. Last we call rainbow_cycle(0), which means it's as fast as it can possibly be. Increase or decrease either of these numbers to speed up or slow down the animations!

Note that the longer your strip of LEDs is, the longer it will take for the animations to complete.

We have a ton more information on general purpose DotStar know-how at our DotStar UberGuide https://learn.adafruit.com/adafruit-dotstar-leds

Is it SPI?

We explained at the beginning of this section that the LEDs respond faster if you're using hardware SPI. On some of the boards, there are HW SPI pins directly available in the form of MOSI and SCK. However, hardware SPI is available on more than just those pins. But, how can you figure out which? Easy! We wrote a handy script.

We chose pins A1 and A2 for our example code. To see if these are hardware SPI on the board you're using, copy and paste the code into code.py using your favorite editor, and save the file. Then connect to the serial console to see the results.

To check if other pin combinations have hardware SPI, change the pin names on the line reading: if is_hardware_SPI(board.A1, board.A2): to the pins you want to use. Then, check the results in the serial console. Super simple!

import board
import busio


def is_hardware_spi(clock_pin, data_pin):
    try:
        p = busio.SPI(clock_pin, data_pin)
        p.deinit()
        return True
    except ValueError:
        return False


# Provide the two pins you intend to use.
if is_hardware_spi(board.A1, board.A2):
    print("This pin combination is hardware SPI!")
else:
    print("This pin combination isn't hardware SPI.")

Read the Docs

For a more in depth look at what dotstar can do, check out DotStar on Read the Docs.

In addition to the USB-serial connection you use for the REPL, there is also a hardware UART you can use. This is handy to talk to UART devices like GPSs, some sensors, or other microcontrollers!

This quick-start example shows how you can create a UART device for communicating with hardware serial devices.

To use this example, you'll need something to generate the UART data. We've used a GPS! Note that the GPS will give you UART data without getting a fix on your location. You can use this example right from your desk! You'll have data to read, it simply won't include your actual location.

Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython Demo - USB/Serial echo

import board
import busio
import digitalio

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

uart = busio.UART(board.TX, board.RX, baudrate=9600)

while True:
    data = uart.read(32)  # read up to 32 bytes
    # print(data)  # this is a bytearray type

    if data is not None:
        led.value = True

        # convert bytearray to string
        data_string = ''.join([chr(b) for b in data])
        print(data_string, end="")

        led.value = False

The Code

First we create the UART object. We provide the pins we'd like to use, board.TX and board.RX, and we set the baudrate=9600. While these pins are labeled on most of the boards, be aware that RX and TX are not labeled on Gemma, and are labeled on the bottom of Trinket. See the diagrams below for help with finding the correct pins on your board.

Once the object is created you read data in with read(numbytes) where you can specify the max number of bytes. It will return a byte array type object if anything was received already. Note it will always return immediately because there is an internal buffer! So read as much data as you can 'digest'.

If there is no data available, read() will return None, so check for that before continuing.

The data that is returned is in a byte array, if you want to convert it to a string, you can use this handy line of code which will run chr() on each byte:

datastr = ''.join([chr(b) for b in data]) # convert bytearray to string

Your results will look something like this:

For more information about the data you're reading and the Ultimate GPS, check out the Ultimate GPS guide: https://learn.adafruit.com/adafruit-ultimate-gps

Wire It Up

You'll need a couple of things to connect the GPS to your board.

For Gemma M0 and Circuit Playground Express, you can use use alligator clips to connect to the Flora Ultimate GPS Module.

For Trinket M0, Feather M0 Express, Metro M0 Express and ItsyBitsy M0 Express, you'll need a breadboard and jumper wires to connect to the Ultimate GPS Breakout.

We've included diagrams show you how to connect the GPS to your board. In these diagrams, the wire colors match the same pins on each board.

  • The black wire connects between the ground pins.
  • The red wire connects between the power pins on the GPS and your board.
  • The blue wire connects from TX on the GPS to RX on your board.
  • The white wire connects from RX on the GPS to TX on your board.

Check out the list below for a diagram of your specific board!

Watch out! A common mixup with UART serial is that RX on one board connects to TX on the other! However, sometimes boards have RX labeled TX and vice versa. So, you'll want to start with RX connected to TX, but if that doesn't work, try the other way around!

Circuit Playground Express and Circuit Playground Bluefruit

  • Connect 3.3v on your CPX to 3.3v on your GPS.
  • Connect GND on your CPX to GND on your GPS.
  • Connect RX/A6 on your CPX to TX on your GPS.
  • Connect TX/A7 on your CPX to RX on your GPS.

Trinket M0

  • Connect USB on the Trinket to VIN on the GPS.
  • Connect Gnd on the Trinket to GND on the GPS.
  • Connect D3 on the Trinket to TX on the GPS.
  • Connect D4 on the Trinket to RX on the GPS.

Gemma M0

  • Connect 3vo on the Gemma to 3.3v on the GPS.
  • Connect GND on the Gemma to GND on the GPS.
  • Connect A1/D2 on the Gemma to TX on the GPS.
  • Connect A2/D0 on the Gemma to RX on the GPS.

Feather M0 Express and Feather M4 Express

  • Connect USB on the Feather to VIN on the GPS.
  • Connect GND on the Feather to GND on the GPS.
  • Connect RX on the Feather to TX on the GPS.
  • Connect TX on the Feather to RX on the GPS.

ItsyBitsy M0 Express and ItsyBitsy M4 Express

  • Connect USB on the ItsyBitsy to VIN on the GPS
  • Connect G on the ItsyBitsy to GND on the GPS.
  • Connect RX/0 on the ItsyBitsy to TX on the GPS.
  • Connect TX/1 on the ItsyBitsy to RX on the GPS.

Metro M0 Express and Metro M4 Express

  • Connect 5V on the Metro to VIN on the GPS.
  • Connect GND on the Metro to GND on the GPS.
  • Connect RX/D0 on the Metro to TX on the GPS.
  • Connect TX/D1 on the Metro to RX on the GPS.

Where's my UART?

On the SAMD21, we have the flexibility of using a wide range of pins for UART. Compare this to some chips like the ESP8266 with fixed UART pins. The good news is you can use many but not all pins. Given the large number of SAMD boards we have, its impossible to guarantee anything other than the labeled 'TX' and 'RX'. So, if you want some other setup, or multiple UARTs, how will you find those pins? Easy! We've written a handy script.

All you need to do is copy this file to your board, rename it code.py, connect to the serial console and check out the output! The results print out a nice handy list of RX and TX pin pairs that you can use.

These are the results from a Trinket M0, your output may vary and it might be very long. For more details about UARTs and SERCOMs check out our detailed guide here

import board
import busio
from microcontroller import Pin


def is_hardware_uart(tx, rx):
    try:
        p = busio.UART(tx, rx)
        p.deinit()
        return True
    except ValueError:
        return False


def get_unique_pins():
    exclude = ['NEOPIXEL', 'APA102_MOSI', 'APA102_SCK']
    pins = [pin for pin in [
        getattr(board, p) for p in dir(board) if p not in exclude]
            if isinstance(pin, Pin)]
    unique = []
    for p in pins:
        if p not in unique:
            unique.append(p)
    return unique


for tx_pin in get_unique_pins():
    for rx_pin in get_unique_pins():
        if rx_pin is tx_pin:
            continue
        else:
            if is_hardware_uart(tx_pin, rx_pin):
                print("RX pin:", rx_pin, "\t TX pin:", tx_pin)
            else:
                pass

Trinket M0: Create UART before I2C

On the Trinket M0 (only), if you are using both UART and I2C, you must create the UART object first, e.g.:

Download: file
>>> import board
>>> uart = board.UART()   # Uses pins 4 and 3 for TX and TX, baudrate 9600.
>>> i2c = board.I2C()     # Uses pins 2 and 0 for SCL and SDA.

# or alternatively,

Creating the I2C object first does not work:

Download: file
>>> import board
>>> i2c = board.I2C()     # Uses pins 2 and 0 for SCL and SDA.
>>> uart = board.UART()   # Uses pins 4 and 3 for TX and TX, baudrate 9600.
Traceback (most recent call last):
File "", line 1, in 
ValueError: Invalid pins

I2C is a 2-wire protocol for communicating with simple sensors and devices, meaning it uses two connections for transmitting and receiving data. There are many I2C devices available and they're really easy to use with CircuitPython. We have libraries available for many I2C devices in the library bundle. (If you don't see the sensor you're looking for, keep checking back, more are being written all the time!)

In this section, we're going to do is learn how to scan the I2C bus for all connected devices. Then we're going to learn how to interact with an I2C device.

We'll be using the TSL2561, a common, low-cost light sensor. While the exact code we're running is specific to the TSL2561 the overall process is the same for just about any I2C sensor or device.

You'll need the adafruit_tsl2561.mpy library and adafruit_bus_device library folder if you don't already have it in your /lib folder! You can get it from the CircuitPython Library Bundle. If you need help installing the library, check out the CircuitPython Libraries page.

These examples will use the TSL2561 lux sensor Flora and breakout. The first thing you'll want to do is get the sensor connected so your board has I2C to talk to.

Wire It Up

You'll need a couple of things to connect the TSL2561 to your board.

For Gemma M0 and Circuit Playground Express, you can use use alligator clips to connect to the Flora TSL2561 Lux Sensor.

For Trinket M0, Feather M0 Express, Metro M0 Express and ItsyBitsy M0 Express, you'll need a breadboard and jumper wires to connect to the TSL2561 Lux Sensor breakout board.

We've included diagrams show you how to connect the TSL2561 to your board. In these diagrams, the wire colors match the same pins on each board.

  • The black wire connects between the ground pins.
  • The red wire connects between the power pins on the TSL2561 and your board.
  • The yellow wire connects from SCL on the TSL2561 to SCL on your board.
  • The blue wire connects from SDA on the TSL2561 to SDA on your board.

Check out the list below for a diagram of your specific board!

Be aware that the Adafruit microcontroller boards do not have I2C pullup resistors built in! All of the Adafruit breakouts do, but if you're building your own board or using a non-Adafruit breakout, you must add 2.2K-10K ohm pullups on both SDA and SCL to the 3.3V.

Circuit Playground Express and Circuit Playground Bluefruit

 

  • Connect 3.3v on your CPX to 3.3v on your TSL2561.
  • Connect GND on your CPX to GND on your TSL2561.
  • Connect SCL/A4 on your CPX to SCL on your TSL2561.
  • Connect SDL/A5 on your CPX to SDA on your TSL2561.

Trinket M0

 

  • Connect USB on the Trinket to VIN on the TSL2561.
  • Connect Gnd on the Trinket to GND on the TSL2561.
  • Connect D2 on the Trinket to SCL on the TSL2561.
  • Connect D0 on the Trinket to SDA on the TSL2561.

Gemma M0

 

  • Connect 3vo on the Gemma to 3V on the TSL2561.
  • Connect GND on the Gemma to GND on the TSL2561.
  • Connect A1/D2 on the Gemma to SCL on the TSL2561.
  • Connect A2/D0 on the Gemma to SDA on the TSL2561.

Feather M0 Express and Feather M4 Express

 

  • Connect USB on the Feather to VIN on the TSL2561.
  • Connect GND on the Feather to GND on the TSL2561.
  • Connect SCL on the Feather to SCL on the TSL2561.
  • Connect SDA on the Feather to SDA on the TSL2561.

ItsyBitsy M0 Express and ItsyBitsy M4 Express

 

  • Connect USB on the ItsyBitsy to VIN on the TSL2561
  • Connect G on the ItsyBitsy to GND on the TSL2561.
  • Connect SCL on the ItsyBitsy to SCL on the TSL2561.
  • Connect SDA on the ItsyBitsy to SDA on the TSL2561.

Metro M0 Express and Metro M4 Express

 

  • Connect 5V on the Metro to VIN on the TSL2561.
  • Connect GND on the Metro to GND on the TSL2561.
  • Connect SCL on the Metro to SCL on the TSL2561.
  • Connect SDA on the Metro to SDA on the TSL2561.

Find Your Sensor

The first thing you'll want to do after getting the sensor wired up, is make sure it's wired correctly. We're going to do an I2C scan to see if the board is detected, and if it is, print out its I2C address.

Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython demo - I2C scan
# 
# If you run this and it seems to hang, try manually unlocking
# your I2C bus from the REPL with
#  >>> import board 
#  >>> board.I2C().unlock() 

import time
import board

i2c = board.I2C()

while not i2c.try_lock():
    pass

try:
    while True:
        print("I2C addresses found:", [hex(device_address)
              for device_address in i2c.scan()])
        time.sleep(2)

finally:  # unlock the i2c bus when ctrl-c'ing out of the loop
    i2c.unlock()

First we create the i2c object, using board.I2C(). This convenience routine creates and saves a busio.I2C object using the default pins board.SCL and board.SDA. If the object has already been created, then the existing object is returned. No matter how many times you call board.I2C(), it will return the same object. This is called a singleton.

To be able to scan it, we need to lock the I2C down so the only thing accessing it is the code. So next we include a loop that waits until I2C is locked and then continues on to the scan function.

Last, we have the loop that runs the actual scan, i2c_scan(). Because I2C typically refers to addresses in hex form, we've included this bit of code that formats the results into hex format: [hex(device_address) for device_address in i2c.scan()].

Open the serial console to see the results! The code prints out an array of addresses. We've connected the TSL2561 which has a 7-bit I2C address of 0x39. The result for this sensor is I2C addresses found: ['0x39']. If no addresses are returned, refer back to the wiring diagrams to make sure you've wired up your sensor correctly.

I2C Sensor Data

Now we know for certain that our sensor is connected and ready to go. Let's find out how to get the data from our sensor!

Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython Demo - I2C sensor

import time

import adafruit_tsl2561
import board

i2c = board.I2C()

# Lock the I2C device before we try to scan
while not i2c.try_lock():
    pass
# Print the addresses found once
print("I2C addresses found:", [hex(device_address)
                               for device_address in i2c.scan()])

# Unlock I2C now that we're done scanning.
i2c.unlock()

# Create library object on our I2C port
tsl2561 = adafruit_tsl2561.TSL2561(i2c)

# Use the object to print the sensor readings
while True:
    print("Lux:", tsl2561.lux)
    time.sleep(1.0)

This code begins the same way as the scan code. We've included the scan code so you have verification that your sensor is wired up correctly and is detected. It prints the address once. After the scan, we unlock I2C with i2c_unlock() so we can use the sensor for data.

We create our sensor object using the sensor library. We call it tsl2561 and provide it the i2c object.

Then we have a simple loop that prints out the lux reading using the sensor object we created. We add a time.sleep(1.0), so it only prints once per second. Connect to the serial console to see the results. Try shining a light on it to see the results change!

Where's my I2C?

On the SAMD21, SAMD51 and nRF52840, we have the flexibility of using a wide range of pins for I2C. On the nRF52840, any pin can be used for I2C! Some chips, like the ESP8266, require using bitbangio, but can also use any pins for I2C. There's some other chips that may have fixed I2C pin.  

The good news is you can use many but not all pins. Given the large number of SAMD boards we have, its impossible to guarantee anything other than the labeled 'SDA' and 'SCL'. So, if you want some other setup, or multiple I2C interfaces, how will you find those pins? Easy! We've written a handy script.

All you need to do is copy this file to your board, rename it code.py, connect to the serial console and check out the output! The results print out a nice handy list of SCL and SDA pin pairs that you can use.

These are the results from an ItsyBitsy M0 Express. Your output may vary and it might be very long. For more details about I2C and SERCOMs, check out our detailed guide here.

import board
import busio
from microcontroller import Pin

def is_hardware_I2C(scl, sda):
    try:
        p = busio.I2C(scl, sda)
        p.deinit()
        return True
    except ValueError:
        return False
    except RuntimeError:
        return True


def get_unique_pins():
    exclude = ['NEOPIXEL', 'APA102_MOSI', 'APA102_SCK']
    pins = [pin for pin in [
        getattr(board, p) for p in dir(board) if p not in exclude]
            if isinstance(pin, Pin)]
    unique = []
    for p in pins:
        if p not in unique:
            unique.append(p)
    return unique


for scl_pin in get_unique_pins():
    for sda_pin in get_unique_pins():
        if scl_pin is sda_pin:
            continue
        else:
            if is_hardware_I2C(scl_pin, sda_pin):
                print("SCL pin:", scl_pin, "\t SDA pin:", sda_pin)
            else:
                pass
These examples have been updated for version 4+ of the CircuitPython HID library. On some boards, such as the CircuitPlayground Express, this library is built into CircuitPython. So, please use the latest version of CircuitPython with these examples. (At least 5.3.1)

One of the things we baked into CircuitPython is 'HID' (Human Interface Device) control - that means keyboard and mouse capabilities. This means your CircuitPython board can act like a keyboard device and press key commands, or a mouse and have it move the mouse pointer around and press buttons. This is really handy because even if you cannot adapt your software to work with hardware, there's almost always a keyboard interface - so if you want to have a capacitive touch interface for a game, say, then keyboard emulation can often get you going really fast!

This section walks you through the code to create a keyboard or mouse emulator. First we'll go through an example that uses pins on your board to emulate keyboard input. Then, we will show you how to wire up a joystick to act as a mouse, and cover the code needed to make that happen.

You'll need the adafruit_hid library folder if you don't already have it in your /lib folder! You can get it from the CircuitPython Library Bundle. If you need help installing the library, check out the CircuitPython Libraries page.

CircuitPython Keyboard Emulator

Copy and paste the code into code.py using your favorite editor, and save the file.

# CircuitPython demo - Keyboard emulator

import time

import board
import digitalio
import usb_hid
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS
from adafruit_hid.keycode import Keycode

# A simple neat keyboard demo in CircuitPython

# The pins we'll use, each will have an internal pullup
keypress_pins = [board.A1, board.A2]
# Our array of key objects
key_pin_array = []
# The Keycode sent for each button, will be paired with a control key
keys_pressed = [Keycode.A, "Hello World!\n"]
control_key = Keycode.SHIFT

# The keyboard object!
time.sleep(1)  # Sleep for a bit to avoid a race condition on some systems
keyboard = Keyboard(usb_hid.devices)
keyboard_layout = KeyboardLayoutUS(keyboard)  # We're in the US :)

# Make all pin objects inputs with pullups
for pin in keypress_pins:
    key_pin = digitalio.DigitalInOut(pin)
    key_pin.direction = digitalio.Direction.INPUT
    key_pin.pull = digitalio.Pull.UP
    key_pin_array.append(key_pin)

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

print("Waiting for key pin...")

while True:
    # Check each pin
    for key_pin in key_pin_array:
        if not key_pin.value:  # Is it grounded?
            i = key_pin_array.index(key_pin)
            print("Pin #%d is grounded." % i)

            # Turn on the red LED
            led.value = True

            while not key_pin.value:
                pass  # Wait for it to be ungrounded!
            # "Type" the Keycode or string
            key = keys_pressed[i]  # Get the corresponding Keycode or string
            if isinstance(key, str):  # If it's a string...
                keyboard_layout.write(key)  # ...Print the string
            else:  # If it's not a string...
                keyboard.press(control_key, key)  # "Press"...
                keyboard.release_all()  # ..."Release"!

            # Turn off the red LED
            led.value = False

    time.sleep(0.01)

Connect pin A1 or A2 to ground, using a wire or alligator clip, then disconnect it to send the key press "A" or the string "Hello world!"

This wiring example shows A1 and A2 connected to ground.

 

Remember, on Trinket, A1 and A2 are labeled 2 and 0! On other boards, you will have A1 and A2 labeled as expected.

Create the Objects and Variables

First, we assign some variables for later use. We create three arrays assigned to variables: keypress_pins, key_pin_array, and keys_pressed. The first is the pins we're going to use. The second is empty because we're going to fill it later. The third is what we would like our "keyboard" to output - in this case the letter "A" and the phrase, "Hello world!". We create our last variable assigned to control_key which allows us to later apply the shift key to our keypress. We'll be using two keypresses, but you can have up to six keypresses at once.

Next keyboard and keyboard_layout objects are created. We only have US right now (if you make other layouts please submit a GitHub pull request!). The time.sleep(1) avoids an error that can happen if the program gets run as soon as the board gets plugged in, before the host computer finishes connecting to the board.

Then we take the pins we chose above, and create the pin objects, set the direction and give them each a pullup. Then we apply the pin objects to key_pin_array so we can use them later.

Next we set up the little red LED to so we can use it as a status light.

The last thing we do before we start our loop is print, "Waiting for key pin..." so you know the code is ready and waiting!

The Main Loop

Inside the loop, we check each pin to see if the state has changed, i.e. you connected the pin to ground. Once it changes, it prints, "Pin # grounded." to let you know the ground state has been detected. Then we turn on the red LED. The code waits for the state to change again, i.e. it waits for you to unground the pin by disconnecting the wire attached to the pin from ground.

Then the code gets the corresponding keys pressed from our array. If you grounded and ungrounded A1, the code retrieves the keypress a, if you grounded and ungrounded A2, the code retrieves the string, "Hello world!"

If the code finds that it's retrieved a string, it prints the string, using the keyboard_layout to determine the keypresses. Otherwise, the code prints the keypress from the control_key and the keypress "a", which result in "A". Then it calls keyboard.release_all(). You always want to call this soon after a keypress or you'll end up with a stuck key which is really annoying!

Instead of using a wire to ground the pins, you can try wiring up buttons like we did in CircuitPython Digital In & Out. Try altering the code to add more pins for more keypress options!

CircuitPython Mouse Emulator

Copy and paste the code into code.py using your favorite editor, and save the file.

import time

import analogio
import board
import digitalio
import usb_hid
from adafruit_hid.mouse import Mouse

mouse = Mouse(usb_hid.devices)

x_axis = analogio.AnalogIn(board.A0)
y_axis = analogio.AnalogIn(board.A1)
select = digitalio.DigitalInOut(board.A2)
select.direction = digitalio.Direction.INPUT
select.pull = digitalio.Pull.UP

pot_min = 0.00
pot_max = 3.29
step = (pot_max - pot_min) / 20.0


def get_voltage(pin):
    return (pin.value * 3.3) / 65536


def steps(axis):
    """ Maps the potentiometer voltage range to 0-20 """
    return round((axis - pot_min) / step)


while True:
    x = get_voltage(x_axis)
    y = get_voltage(y_axis)

    if select.value is False:
        mouse.click(Mouse.LEFT_BUTTON)
        time.sleep(0.2)  # Debounce delay

    if steps(x) > 11.0:
        # print(steps(x))
        mouse.move(x=1)
    if steps(x) < 9.0:
        # print(steps(x))
        mouse.move(x=-1)

    if steps(x) > 19.0:
        # print(steps(x))
        mouse.move(x=8)
    if steps(x) < 1.0:
        # print(steps(x))
        mouse.move(x=-8)

    if steps(y) > 11.0:
        # print(steps(y))
        mouse.move(y=-1)
    if steps(y) < 9.0:
        # print(steps(y))
        mouse.move(y=1)

    if steps(y) > 19.0:
        # print(steps(y))
        mouse.move(y=-8)
    if steps(y) < 1.0:
        # print(steps(y))
        mouse.move(y=8)

For this example, we've wired up a 2-axis thumb joystick with a select button. We use this to emulate the mouse movement and the mouse left-button click. To wire up this joytick:

  • Connect VCC on the joystick to the 3V on your board. Connect ground to ground.
  • Connect Xout on the joystick to pin A0 on your board.
  • Connect Yout on the joystick to pin A1 on your board.
  • Connect Sel on the joystick to pin A2 on your board.

Remember, Trinket's pins are labeled differently. Check the Trinket Pinouts page to verify your wiring.

 

To use this demo, simply move the joystick around. The mouse will move slowly if you move the joystick a little off center, and more quickly if you move it as far as it goes. Press down on the joystick to click the mouse. Awesome! Now let's take a look at the code.

Create the Objects and Variables

First we create the mouse object.

Next, we set x_axis and y_axis to pins A0 and A1. Then we set select to A2, set it as input and give it a pullup.

The x and y axis on the joystick act like 2 potentiometers. We'll be using them just like we did in CircuitPython Analog In. We set pot_min and pot_max to be the minimum and maximum voltage read from the potentiometers. We assign step = (pot_max - pot_min) / 20.0 to use in a helper function.

CircuitPython HID Mouse Helpers

First we have the get_voltage() helper so we can get the correct readings from the potentiometers. Look familiar? We learned about it in Analog In.

Second, we have steps(axis). To use it, you provide it with the axis you're reading. This is where we're going to use the step variable we assigned earlier. The potentiometer range is 0-3.29. This is a small range. It's even smaller with the joystick because the joystick sits at the center of this range, 1.66, and the + and - of each axis is above and below this number. Since we need to have thresholds in our code, we're going to map that range of 0-3.29 to while numbers between 0-20.0 using this helper function. That way we can simplify our code and use larger ranges for our thresholds instead of trying to figure out tiny decimal number changes.

Main Loop

First we assign x and y to read the voltages from x_axis and y_axis.

Next, we check to see when the state of the select button is False. It defaults to True when it is not pressed, so if the state is False, the button has been pressed. When it's pressed, it sends the command to click the left mouse button. The time.sleep(0.2) prevents it from reading multiple clicks when you've only clicked once.

Then we use the steps() function to set our mouse movement. There are two sets of two if statements for each axis. Remember that 10 is the center step, as we've mapped the range 0-20. The first set for each axis says if the joystick moves 1 step off center (left or right for the x axis and up or down for the y axis), to move the mouse the appropriate direction by 1 unit. The second set for each axis says if the joystick is moved to the lowest or highest step for each axis, to move the mouse the appropriate direction by 8 units. That way you have the option to move the mouse slowly or quickly!

To see what step the joystick is at when you're moving it, uncomment the print statements by removing the from the lines that look like # print(steps(x)), and connecting to the serial console to see the output. Consider only uncommenting one set at a time, or you end up with a huge amount of information scrolling very quickly, which can be difficult to read!

For more detail check out the documentation at https://circuitpython.readthedocs.io/projects/hid/en/latest/

CircuitPython boards show up as as USB drive, allowing you to edit code directly on the board. You've been doing this for a while. By now, maybe you've wondered, "Can I write data from CircuitPython to the storage drive to act as a datalogger?" The answer is yes!

However, it is a little tricky. You need to add some special code to boot.py, not just code.py. That's because you have to set the filesystem to be read-only when you need to edit code to the disk from your computer, and set it to writeable when you want the CircuitPython core to be able to write.

You can only have either your computer edit the CIRCUITPY drive files, or CircuitPython. You cannot have both write to the drive at the same time. (Bad Things Will Happen so we do not allow you to do it!)

The following is your new boot.py. Copy and paste the code into boot.py using your favorite editor. You may need to create a new file.

import board
import digitalio
import storage

# For Gemma M0, Trinket M0, Metro M0/M4 Express, ItsyBitsy M0/M4 Express
switch = digitalio.DigitalInOut(board.D2)

# For Feather M0/M4 Express
# switch = digitalio.DigitalInOut(board.D5)

# For Circuit Playground Express, Circuit Playground Bluefruit
# switch = digitalio.DigitalInOut(board.D7)

switch.direction = digitalio.Direction.INPUT
switch.pull = digitalio.Pull.UP

# If the switch pin is connected to ground CircuitPython can write to the drive
storage.remount("/", switch.value)

For Gemma M0, Trinket M0, Metro M0 Express, Metro M4 Express, ItsyBitsy M0 Express and ItsyBitsy M4 Express, no changes to the initial code are needed.

For Feather M0 Express and Feather M4 Express, comment out switch = digitalio.DigitalInOut(board.D2), and uncomment switch = digitalio.DigitalInOut(board.D5).

For Circuit Playground Express and Circuit Playground Bluefruit, comment out switch = digitalio.DigitalInOut(board.D2), and uncomment switch = digitalio.DigitalInOut(board.D7). Remember, D7 is the onboard slide switch, so there's no extra wires or alligator clips needed.

Remember: To "comment out" a line, put a # and a space before it. To "uncomment" a line, remove the # + space from the beginning of the line.

The following is your new code.py. Copy and paste the code into code.py using your favorite editor.

import time

import board
import digitalio
import microcontroller

led = digitalio.DigitalInOut(board.D13)
led.switch_to_output()

try:
    with open("/temperature.txt", "a") as fp:
        while True:
            temp = microcontroller.cpu.temperature
            # do the C-to-F conversion here if you would like
            fp.write('{0:f}\n'.format(temp))
            fp.flush()
            led.value = not led.value
            time.sleep(1)
except OSError as e:
    delay = 0.5
    if e.args[0] == 28:
        delay = 0.25
    while True:
        led.value = not led.value
        time.sleep(delay)

Logging the Temperature

The way boot.py works is by checking to see if the pin you specified in the switch setup in your code is connected to a ground pin. If it is, it changes the read-write state of the file system, so the CircuitPython core can begin logging the temperature to the board.

For help finding the correct pins, see the wiring diagrams and information in the Find the Pins section of the CircuitPython Digital In & Out guide. Instead of wiring up a switch, however, you'll be connecting the pin directly to ground with alligator clips or jumper wires.

boot.py only runs on first boot of the device, not if you re-load the serial console with ctrl+D or if you save a file. You must EJECT the USB drive, then physically press the reset button!

Once you copied the files to your board, eject it and unplug it from your computer. If you're using your Circuit Playground Express, all you have to do is make sure the switch is to the right. Otherwise, use alligator clips or jumper wires to connect the chosen pin to ground. Then, plug your board back into your computer.

You will not be able to edit code on your CIRCUITPY drive anymore!

The red LED should blink once a second and you will see a new temperature.txt file on CIRCUITPY.

This file gets updated once per second, but you won't see data come in live. Instead, when you're ready to grab the data, eject and unplug your board. For CPX, move the switch to the left, otherwise remove the wire connecting the pin to ground. Now it will be possible for you to write to the filesystem from your computer again, but it will not be logging data.

We have a more detailed guide on this project available here: CPU Temperature Logging with CircuitPython. If you'd like more details, check it out!

There is a CPU temperature sensor built into every ATSAMD21, ATSAMD51 and nRF52840 chips. CircuitPython makes it really simple to read the data from this sensor. This works on the Adafruit CircuitPython boards it's built into the microcontroller used for these boards.

The data is read using two simple commands. We're going to enter them in the REPL. Plug in your board, connect to the serial console, and enter the REPL. Then, enter the following commands into the REPL:

Download: file
import microcontroller
microcontroller.cpu.temperature

That's it! You've printed the temperature in Celsius to the REPL. Note that it's not exactly the ambient temperature and it's not super precise. But it's close!

If you'd like to print it out in Fahrenheit, use this simple formula: Celsius * (9/5) + 32. It's super easy to do math using CircuitPython. Check it out!

Note that the temperature sensor built into the nRF52840 has a resolution of 0.25 degrees Celsius, so any temperature you print out will be in 0.25 degree increments.
As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit https://circuitpython.org/downloads to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit https://circuitpython.org/libraries to download the latest Library Bundle.

Always Run the Latest Version of CircuitPython and Libraries

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. You need to update to the latest CircuitPython.

You need to download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then download the latest bundle.

As we release new versions of CircuitPython, we will stop providing the previous bundles as automatically created downloads on the Adafruit CircuitPython Library Bundle repo. If you must continue to use an earlier version, you can still download the appropriate version of mpy-cross from the particular release of CircuitPython on the CircuitPython repo and create your own compatible .mpy library files. However, it is best to update to the latest for both CircuitPython and the library bundle.

I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 2.x and 3.x library bundles. We highly encourage you to update CircuitPython to the latest version and use the current version of the libraries. However, if for some reason you cannot update, you can find the last available 2.x build here and the last available 3.x build here.

Switching Between CircuitPython and Arduino

Many of the CircuitPython boards also run Arduino. But how do you switch between the two? Switching between CircuitPython and Arduino is easy.

If you're currently running Arduino and would like to start using CircuitPython, follow the steps found in Welcome to CircuitPython: Installing CircuitPython.

If you're currently running CircuitPython and would like to start using Arduino, plug in your board, and then load your Arduino sketch. If there are any issues, you can double tap the reset button to get into the bootloader and then try loading your sketch. Always backup any files you're using with CircuitPython that you want to save as they could be deleted.

That's it! It's super simple to switch between the two.

The Difference Between Express And Non-Express Boards

We often reference "Express" and "Non-Express" boards when discussing CircuitPython. What does this mean?

Express refers to the inclusion of an extra 2MB flash chip on the board that provides you with extra space for CircuitPython and your code. This means that we're able to include more functionality in CircuitPython and you're able to do more with your code on an Express board than you would on a non-Express board.

Express boards include Circuit Playground Express, ItsyBitsy M0 Express, Feather M0 Express, Metro M0 Express and Metro M4 Express.

Non-Express boards include Trinket M0, Gemma M0, Feather M0 Basic, and other non-Express Feather M0 variants.

Non-Express Boards: Gemma and Trinket

CircuitPython runs nicely on the Gemma M0 or Trinket M0 but there are some constraints

Small Disk Space

Since we use the internal flash for disk, and that's shared with runtime code, its limited! Only about 50KB of space.

No Audio or NVM

Part of giving up that FLASH for disk means we couldn't fit everything in. There is, at this time, no support for hardware audio playpack or NVM 'eeprom'. Modules audioio and bitbangio are not included. For that support, check out the Circuit Playground Express or other Express boards.

However, I2C, UART, capacitive touch, NeoPixel, DotStar, PWM, analog in and out, digital IO, logging storage, and HID do work! Check the CircuitPython Essentials for examples of all of these.

Differences Between CircuitPython and MicroPython

For the differences between CircuitPython and MicroPython, check out the CircuitPython documentation.

Differences Between CircuitPython and Python

Python (also known as CPython) is the language that MicroPython and CircuitPython are based on. There are many similarities, but there are also many differences. This is a list of a few of the differences.

Python Libraries

Python is advertised as having "batteries included", meaning that many standard libraries are included. Unfortunately, for space reasons, many Python libraries are not available. So for instance while we wish you could import numpy, numpy isn't available. So you may have to port some code over yourself!

Integers in CircuitPython

On the non-Express boards, integers can only be up to 31 bits long. Integers of unlimited size are not supported. The largest positive integer that can be represented is 230-1, 1073741823, and the most negative integer possible is -230, -1073741824.

As of CircuitPython 3.0, Express boards have arbitrarily long integers as in Python.

Floating Point Numbers and Digits of Precision for Floats in CircuitPython

Floating point numbers are single precision in CircuitPython (not double precision as in Python). The largest floating point magnitude that can be represented is about +/-3.4e38. The smallest magnitude that can be represented with full accuracy is about +/-1.7e-38, though numbers as small as +/-5.6e-45 can be represented with reduced accuracy.

CircuitPython's floats have 8 bits of exponent and 22 bits of mantissa (not 24 like regular single precision floating point), which is about five or six decimal digits of precision.

Differences between MicroPython and Python

For a more detailed list of the differences between CircuitPython and Python, you can look at the MicroPython documentation. We keep up with MicroPython stable releases, so check out the core 'differences' they document here.

To help you get your Bluefruit LE module talking to other Central devices, we've put together a number of open source tools for most of the major platforms supporting Bluetooth Low Energy.

Bluefruit LE Client Apps and Libraries

Adafruit has put together the following mobile or desktop apps and libraries to make it as easy as possible to get your Bluefruit LE module talking to your mobile device or laptop, with full source available where possible:

Bluefruit LE Connect (Android/Java)

Bluetooth Low Energy support was added to Android starting with Android 4.3 (though it was only really stable starting with 4.4), and we've already released Bluefruit LE Connect to the Play Store.

The full source code for Bluefruit LE Connect for Android is also available on Github to help you get started with your own Android apps.  You'll need a recent version of Android Studio to use this project.

Bluefruit LE Connect  (iOS/Swift)

Apple was very early to adopt Bluetooth Low Energy, and we also have an iOS version of the Bluefruit LE Connect app available in Apple's app store.

The full swift source code for Bluefruit LE Connect for iOS is also available on Github. You'll need XCode and access to Apple's developper program to use this project:

Version 2.x of the app is a complete rewrite that includes iOS, OS X GUI and OS X command-line tools in a single codebase.

Bluefruit LE Connect for OS X (Swift)

This OS X desktop application is based on the same V2.x codebase as the iOS app, and gives you access to BLE UART, basic Pin I/O and OTA DFU firmware updates from the convenience of your laptop or mac.

This is a great choice for logging sensor data locally and exporting it as a CSV, JSON or XML file for parsing in another application, and uses the native hardware on your computer so no BLE dongle is required on any recent mac.

The full source is also available on Github.

Bluefruit LE Command Line Updater for OS X (Swift)

This experimental command line tool is unsupported and provided purely as a proof of concept, but can be used to allow firmware updates for Bluefruit devices from the command line.

This utility performs automatic firmware updates similar to the way that the GUI application does, by checking the firmware version on your Bluefruit device (via the Device Information Service), and comparing this against the firmware versions available online, downloading files in the background if appropriate.

Simply install the pre-compiled tool via the DMG file and place it somewhere in the system path, or run the file locally via './bluefruit' to see the help menu:

Download: file
$ ./bluefruit
bluefruit v0.3
Usage:
	bluefruit <command> [options...]

Commands:
	Scan peripherals:   scan
	Automatic update:   update [--enable-beta] [--uuid <uuid>]
	Custom firmware:    dfu --hex <filename> [--init <filename>] [--uuid <uuid>]
	Show this screen:   --help
	Show version:       --version

Options:
	--uuid <uuid>    If present the peripheral with that uuid is used. If not present a list of peripherals is displayed
	--enable-beta    If not present only stable versions are used

Short syntax:
	-u = --uuid, -b = --enable-beta, -h = --hex, -i = --init, -v = --version, -? = --help

Deprecated: Bluefruit Buddy (OS X)

This native OS X application is a basic proof of concept app that allows you to connect to your Bluefruit LE module using most recent macbooks or iMacs. You can get basic information about the modules and use the UART service to send and receive data.

The full source for the application is available in the github repo at Adafruit_BluefruitLE_OSX.

ABLE (Cross Platform/Node+Electron)

ABLE (Adafruit Bluefruit LE Desktop) is a cross-platform desktop application based on Sandeep Misty's noble library and the Electron project from Github (used by Atom).

It runs on OS X, Windows 7+ and select flavours of Linux (Ubuntu tested locally).  Windows 7 support is particularly interesting since Windows 7 has no native support for Bluetooth Low Energy but the noble library talks directly to supported Bluetooth 4.0 USB dongles to emulate BLE on the system (though at this stage it's still in early BETA and drops the connection and takes more care to work with).

This app allows you to collect sensor data or perform many of the same functionality offered by the mobile Bluefruit LE Connect apps, but on the desktop.

The app is still in BETA, but full source is available in addition to the easy to use pre-compiled binaries.

Bluefruit LE Python Wrapper

As a proof of concept, we've played around a bit with getting Python working with the native Bluetooth APIs on OS X and the latest version of Bluez on certain Linux targets.

There are currently example sketches showing how to retreive BLE UART data as well as some basic details from the Device Information Service (DIS).

This isn't an actively support project and was more of an experiment, but if you have a recent Macbook or a Raspberry Pi and know Python, you might want to look at Adafruit_Python_BluefruitLE in our github account.

Debug Tools

If your sense of adventure gets the better of you, and your Bluefruit LE module goes off into the weeds, the following tools might be useful to get it back from unknown lands.

These debug tools are provided purely as a convenience for advanced users for device recovery purposes, and are not recommended unless you're OK with potentially bricking your board. Use them at your own risk.

AdaLink (Python)

This command line tool is a python-based wrapper for programming ARM MCUs using either a Segger J-Link or an STLink/V2. You can use it to reflash your Bluefruit LE module using the latest firmware from the Bluefruit LE firmware repo.

Details on how to use the tool are available in the readme.md file on the main Adafruit_Adalink repo on Github.

Completely reprogramming a Bluefruit LE module with AdaLink would require four files, and would look something like this (using a JLink):

Download: file
adalink nrf51822 --programmer jlink --wipe
  --program-hex "Adafruit_BluefruitLE_Firmware/softdevice/s110_nrf51_8.0.0_softdevice.hex" 
  --program-hex "Adafruit_BluefruitLE_Firmware/bootloader/bootloader_0002.hex"
  --program-hex "Adafruit_BluefruitLE_Firmware/0.6.7/blefriend32/blefriend32_s110_xxac_0_6_7_150917_blefriend32.hex"
  --program-hex "Adafruit_BluefruitLE_Firmware/0.6.7/blefriend32/blefriend32_s110_xxac_0_6_7_150917_blefriend32_signature.hex"

You can also use the AdaLink tool to get some basic information about your module, such as which SoftDevice is currently programmed or the IC revision (16KB SRAM or 32KB SRAM) via the --info command:

Download: file
$ adalink nrf51822 -p jlink --info
Hardware ID : QFACA10 (32KB)
Segger ID   : nRF51822_xxAC
SD Version  : S110 8.0.0
Device Addr : **:**:**:**:**:**
Device ID   : ****************

Adafruit nRF51822 Flasher (Python)

Adafruit's nRF51822 Flasher is an internal Python tool we use in production to flash boards as they go through the test procedures and off the assembly line, or just testing against different firmware releases when debugging.

It relies on AdaLink or OpenOCD beneath the surface (see above), but you can use this command line tool to flash your nRF51822 with a specific SoftDevice, Bootloader and Bluefruit firmware combination.

It currently supports using either a Segger J-Link or STLink/V2 via AdaLink, or GPIO on a Raspberry Pi if you don't have access to a traditional ARM SWD debugger.  (A pre-built version of OpenOCD for the RPi is included in the repo since building it from scratch takes a long time on the original RPi.)

We don't provide active support for this tool since it's purely an internal project, but made it public just in case it might help an adventurous customer debrick a board on their own.

Download: file
$ python flash.py --jtag=jlink --board=blefriend32 --softdevice=8.0.0 --bootloader=2 --firmware=0.6.7
jtag       	: jlink
softdevice 	: 8.0.0
bootloader 	: 2
board      	: blefriend32
firmware   	: 0.6.7
Writing Softdevice + DFU bootloader + Application to flash memory
adalink -v nrf51822 --programmer jlink --wipe --program-hex "Adafruit_BluefruitLE_Firmware/softdevice/s110_nrf51_8.0.0_softdevice.hex" --program-hex "Adafruit_BluefruitLE_Firmware/bootloader/bootloader_0002.hex" --program-hex "Adafruit_BluefruitLE_Firmware/0.6.7/blefriend32/blefriend32_s110_xxac_0_6_7_150917_blefriend32.hex" --program-hex "Adafruit_BluefruitLE_Firmware/0.6.7/blefriend32/blefriend32_s110_xxac_0_6_7_150917_blefriend32_signature.hex"
...

Files:

Module Details

The Bluefruit nRF52840 Feather Express uses the MDBT50Q module from Raytac. Details on the module, including FCC and other certifications are available in the document below:

Schematic

Click on the image for full-size versions.

Board Design

The board files are available on Github, and the board has the following physical layout:

This guide was first published on Jan 18, 2020. It was last updated on Jan 18, 2020.