Feather is the new development board from Adafruit, and like its namesake it is thin, light, and lets you fly! We designed Feather to be a new standard for portable microcontroller cores.

This is the Adafruit Feather 32u4 Radio (RFM69HCW) - our take on an microcontroller packet radio transceiver with built in USB and battery charging. Its an Adafruit Feather 32u4 with a 433 or 868/915 MHz radio module cooked in! Great for making wireless networks that can go further than 2.4GHz 802.15.4 and similar, are more flexible than Bluetooth LE and without the high power requirements of WiFi. We have other boards in the Feather family, check'em out here

At the Feather 32u4's heart is at ATmega32u4 clocked at 8 MHz and at 3.3V logic, a chip setup we've had tons of experience with as it's the same as the Flora. This chip has 32K of flash and 2K of RAM, with built in USB so not only does it have a USB-to-Serial program & debug capability built in with no need for an FTDI-like chip, it can also act like a mouse, keyboard, USB MIDI device, etc.

To make it easy to use for portable projects, we added a connector for any of our 3.7V Lithium polymer batteries and built in battery charging. You don't need a battery, it will run just fine straight from the micro USB connector. But, if you do have a battery, you can take it on the go, then plug in the USB to recharge. The Feather will automatically switch over to USB power when its available. We also tied the battery thru a divider to an analog pin, so you can measure and monitor the battery voltage to detect when you need a recharge.

Here's some handy specs! Like all Feather 32u4's you get:

• Measures 2.0" x 0.9" x 0.28" (51mm x 23mm x 8mm) without headers soldered in
• Light as a (large?) feather - 5.5 grams
• ATmega32u4 @ 8MHz with 3.3V logic/power
• 3.3V regulator with 500mA peak current output
• USB native support, comes with USB bootloader and serial port debugging
• You also get tons of pins - 20 GPIO pins
• Hardware Serial, hardware I2C, hardware SPI support
• 7 x PWM pins
• 10 x analog inputs
• Built in 100mA lipoly charger with charging status indicator LED
• Pin #13 red LED for general purpose blinking
• Power/enable pin
• 4 mounting holes
• Reset button

The Feather 32u4 Radio uses the extra space left over to add an RFM69HCW 433 or 868/915 MHz radio module. These radios are not good for transmitting audio or video, but they do work quite well for small data packet transmission when you ned more range than 2.4 GHz (BT, BLE, WiFi, ZigBee)

• SX1231 based module with SPI interface
• Packet radio with ready-to-go Arduino libraries
• Uses the amateur or license-free ISM bands: 433MHz is ITU "Europe" license-free ISM or ITU "American" amateur with limitations. 900MHz is license-free ISM for ITU "Americas"
• +13 to +20 dBm up to 100 mW Power Output Capability (power output selectable in software)
• Create multipoint networks with individual node addresses
• Encrypted packet engine with AES-128
• Simple wire antenna or spot for uFL connector

Comes fully assembled and tested, with a USB bootloader that lets you quickly use it with the Arduino IDE. We also toss in some header so you can solder it in and plug into a solderless breadboard. You will need to cut and solder on a small piece of wire (any solid or stranded core is fine) in order to create your antenna. Lipoly battery and USB cable not included but we do have lots of options in the shop if you'd like!

Click here to view a PDF version of the pinout diagram

Click here to view a PDF version of the pinout diagram

The Feather 32u4 Radio is chock-full of microcontroller goodness. There's also a lot of pins and ports. We'll take you a tour of them now!

Note that the pinouts are identical for both the Feather 32u4 RFM69 and LoRa radios - you can look at the silkscreen of the Feather to see it says "RFM69" or "LoRa"

Pinouts are also the same for both 433MHz and 900Mhz. You can tell the difference by looking for a colored dot on the chip or crystal of the radio, green/blue is 900MHz & red is 433MHz

Power Pins

• GND - this is the common ground for all power and logic
• BAT - this is the positive voltage to/from the JST jack for the optional Lipoly battery
• USB - this is the positive voltage to/from the micro USB jack if connected
• EN - this is the 3.3V regulator's enable pin. It's pulled up, so connect to ground to disable the 3.3V regulator
• 3V - this is the output from the 3.3V regulator, it can supply 500mA peak

Logic pins

This is the general purpose I/O pin set for the microcontroller. All logic is 3.3V

• #0 / RX - GPIO #0, also receive (input) pin for Serial1 and Interrupt #2
• #1 / TX - GPIO #1, also transmit (output) pin for Serial1 and Interrupt #3
  
• #2 / SDA - GPIO #2, also the I2C (Wire) data pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Also Interrupt #1
• #3 / SCL - GPIO #3, also the I2C (Wire) clock pin. There's no pull up on this pin by default so when using with I2C, you may need a 2.2K-10K pullup. Can also do PWM output and act as Interrupt #0.
• #5 - GPIO #5, can also do PWM output
• #6 - GPIO #6, can also do PWM output and analog input A7
• #9 - GPIO #9, also analog input A9 and can do PWM output. This analog input is connected to a voltage divider for the lipoly battery so be aware that this pin naturally 'sits' at around 2VDC due to the resistor divider
• #10 - GPIO #10, also analog input A10 and can do PWM output.
• #11 - GPIO #11, can do PWM output.
• #12 - GPIO #12, also analog input A11 and can do PWM output.
• #13 - GPIO #13, can do PWM output and is connected to the red LED next to the USB jack
• A0 thru A5 - These are each analog input as well as digital I/O pins.
• SCK/MOSI/MISO - These are the hardware SPI pins, used by the RFM radio module too! You can use them as everyday GPIO pins if you don't activate the radio and keep the RFM CS pin high. However, we really recommend keeping them free as they should be kept available for the radio module. If they are used, make sure its with a device that will kindly share the SPI bus! Also used to reprogram the chip with an AVR programmer if you need.

RFM/SemTech Radio Module

Since not all pins can be brought out to breakouts, due to the small size of the Feather, we use these to control the radio module

• #8 - used as the radio CS (chip select) pin
• #7 - used as the radio GPIO0 / IRQ (interrupt request) pin.
• #4 - used as the radio Reset pin

Since these are not brought out there should be no risk of using them by accident!

There are also breakouts for 3 of the RFM's GPIO pins (IO1, IO2 and IO3). You probably wont need these for most uses of the Feather but they are available in case you need 'em!

Other Pins!

• RST - this is the Reset pin, tie to ground to manually reset the AVR, as well as launch the bootloader manually
• ARef - the analog reference pin. Normally the reference voltage is the same as the chip logic voltage (3.3V) but if you need an alternative analog reference, connect it to this pin and select the external AREF in your firmware. Can't go higher than 3.3V!

Your Feather Radio does not have a built-in antenna. Instead, you have two options for attaching an antenna. For most low cost radio nodes, a short length of wire works great. If you need to put the Feather into an enclosure, soldering on a uFL connector (on Feathers that don’t already include this) and using a uFL to SMA adapter will let you attach an external antenna.

Wire Antenna

A wire antenna, aka "quarter wave whip antenna" is low cost and works very well! You just have to cut the wire down to the right length.

uFL Antenna

If you want an external antenna, you need to do a tiny bit more work but its not too difficult.

For Feather Radio boards that don’t already have a surface-mount uFL connector installed, you’ll need to get one. Feather RP2040 RFM boards already have this installed. Feather M0 and 32u4 require soldering.

You'll also need a uFL to SMA adapter (or whatever adapter you need for the antenna you'll be using, SMA is the most common).

Of course, you will also need an antenna of some sort, one that matches your radio frequency.

For Feather M0 and 32u4:

(this step can be skipped for Feather RP2040 RFM, which already has a uFL connector installed)

For all radio-capable Feather boards:

Battery + USB Power

We wanted to make our Feather boards easy to power both when connected to a computer as well as via battery.

There's two ways to power a Feather:

1. You can connect with a USB cable (just plug into the jack) and the Feather will regulate the 5V USB down to 3.3V.
2. You can also connect a 4.2/3.7V Lithium Polymer (LiPo/LiPoly) or Lithium Ion (LiIon) battery to the JST jack. This will let the Feather run on a rechargeable battery.

When the USB power is powered, it will automatically switch over to USB for power, as well as start charging the battery (if attached). This happens 'hot-swap' style so you can always keep the LiPoly connected as a 'backup' power that will only get used when USB power is lost.

The above shows the Micro USB jack (left), LiPoly JST jack (top left), as well as the 3.3V regulator and changeover diode (just to the right of the JST jack) and the LiPoly charging circuitry (to the right of the Reset button).

There's also a CHG LED next to the USB jack, which will light up while the battery is charging. This LED might also flicker if the battery is not connected, it's normal.

Power Supplies

You have a lot of power supply options here! We bring out the BAT pin, which is tied to the LiPoly JST connector, as well as USB which is the +5V from USB if connected. We also have the 3V pin which has the output from the 3.3V regulator. We use a 500mA peak regulator. While you can get 500mA from it, you can't do it continuously from 5V as it will overheat the regulator.

It's fine for, say, powering an ESP8266 WiFi chip or XBee radio though, since the current draw is 'spiky' & sporadic.

Measuring Battery

If you're running off of a battery, chances are you wanna know what the voltage is at! That way you can tell when the battery needs recharging. LiPoly batteries are 'maxed out' at 4.2V and stick around 3.7V for much of the battery life, then slowly sink down to 3.2V or so before the protection circuitry cuts it off. By measuring the voltage you can quickly tell when you're heading below 3.7V.

To make this easy we stuck a double-100K resistor divider on the BAT pin, and connected it to D9 (a.k.a analog #7 A7). You can read this pin's voltage, then double it, to get the battery voltage.

This voltage will 'float' at 4.2V when no battery is plugged in, due to the lipoly charger output, so its not a good way to detect if a battery is plugged in or not (there is no simple way to detect if a battery is plugged in)

ENable pin

If you'd like to turn off the 3.3V regulator, you can do that with the EN(able) pin. Simply tie this pin to Ground and it will disable the 3V regulator. The BAT and USB pins will still be powered.

Alternative Power Options

The two primary ways for powering a feather are a 3.7/4.2V LiPo battery plugged into the JST port or a USB power cable.

If you need other ways to power the Feather, here's what we recommend:

• For permanent installations, a 5V 1A USB wall adapter will let you plug in a USB cable for reliable power
• For mobile use, where you don't want a LiPoly, use a USB battery pack!
• If you have a higher voltage power supply, use a 5V buck converter and wire it to a USB cable's 5V and GND input

Here's what you cannot do:

• Do not use alkaline or NiMH batteries and connect to the battery port - this will destroy the LiPoly charger
• Do not use 7.4V RC batteries on the battery port - this will destroy the board

The Feather is not designed for external power supplies - this is a design decision to make the board compact and low cost. It is not recommended, but technically possible:

• Connect an external 3.3V power supply to the 3V and GND pins. Not recommended, this may cause unexpected behavior and the EN pin will no longer work. Also this doesn't provide power on BAT or USB and some Feathers/Wings use those pins for high current usages. You may end up damaging your Feather.
• Connect an external 5V power supply to the USB and GND pins. Not recommended, this may cause unexpected behavior when plugging in the USB port because you will be back-powering the USB port, which could confuse or damage your computer.

Radio Power Draw

You can select the power output you want via software, more power equals more range but of course, uses more of your battery.

For example, here is the feather 32u4 with RFM69HCW set up for +20dBm power, transmitting a data payload of 20 bytes

The ~25mA quiescent current is the current draw for listening (~15mA) plus ~10mA for the microcontroller. This can be reduce to amost nothing with proper sleep modes and not putting the module in active listen mode!

Here is a transmit with radio.setPowerLevel(0) to set +5dBm power

You still have the 25mA average, but during transmit, it only uses another 20mA not 100mA

If you put the radio to sleep after transmitting, rather than just sitting in receive mode, you can save more current, after transmit is complete, the average current drops to ~10mA which is just for the microcontroller

If you want to reduce even more power, use the Adafruit Sleepdog library by installing and adding #include "Adafruit_SleepyDog.h" at the top of your sketch and replace

delay(1000); 

with

radio.sleep();
Watchdog.sleep(1000);

To put the chip into ultra-low-power mode. Note that USB will disconnect so do this after you have done all your debugging!

During the super sleepy mode you're using only 300uA (0.3mA)!

While its not easy to get the exact numbers for all of what comprise the 300uA there are a few quiescent current items on the Feather 32u4:

• 2 x 100K resistors for VBAT measurement = 25uA
• AP2112K 3.3V regulator = 55uA
• MCP73871 batt charger = up to 100uA even when no battery is connected

The rest is probably the Atmega32u4 peripherals including the brown-out detect and bandgap circuitry, ceramic oscillator, etc. According to the datasheet, with the watchdog and BrownOutDetect enabled, the lowest possible current is ~30uA (at 5V which is what we're testing at)

Before beginning make sure you have your Arduino or Feather working smoothly, it will make this part a lot easier. Once you have the basic functionality going - you can upload code, blink an LED, use the serial output, etc. you can then upgrade to using the radio itself.

Note that the sub-GHz radio is not designed for streaming audio or video! It's best used for small packets of data. The data rate is adjustable but its common to stick to around 19.2 Kbps (thats bits per second). Lower data rates will be more successful in their transmissions

You will, of course, need at least two paired radios to do any testing! The radios must be matched in frequency (e.g. two 900 MHz  radios are ok, but mixing 900 MHz and 433 MHz is not). They also must use the same encoding schemes, you cannot have a 900 MHz RFM69 packet radio talk to a 900 MHz RFM9x LoRa radio.

"Raw" vs Packetized

The SX1231 can be used in a 'raw rx/tx' mode where it just modulates incoming bits from pin #2 and sends them on the radio, however there's no error correction or addressing so we wont be covering that technique.

Instead, 99% of cases are best off using packetized mode. This means you can set up a recipient for your data, error correction so you can be sure the whole data set was transmitted correctly, automatic re-transmit retries and return-receipt when the packet was delivered. Basically, you get the transparency of a data pipe without the annoyances of radio transmission unreliability

Arduino Libraries

These radios have really great libraries already written, so rather than coming up with a new standard we suggest using existing libraries such as LowPowerLab's RFM69 Library and AirSpayce's Radiohead library which also suppors a vast number of other radios

These are really great Arduino Libraries, so please support both companies in thanks for their efforts!

We recommend using the Radiohead library - it is very cross-platform friendly and used a lot in the community!

RadioHead Library example

To begin talking to the radio, you will need to download our fork of the Radiohead library from our github repository. You can do that by visiting the github repo and manually downloading or, easier, just click this button to download the zip:

Rename the uncompressed folder RadioHead and check that the RadioHead folder contains files like RH_RF69.cpp and RH_RF69.h (and many others!)

Place the RadioHead library folder in your arduinosketchfolder/libraries/ folder.
You may need to create the libraries subfolder if it's your first library. Restart the IDE.

We also have a great tutorial on Arduino library installation at:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use

Basic RX & TX example

Lets get a basic demo going, where one radio transmits and the other receives. We'll start by setting up the transmitter

Basic Transmitter example code

This code will send a small packet of data once a second to another RFM69 radio, without any addressing.

Open up the example RadioHead→feather→RadioHead69_RawDemo_TX

Load this code into your Transmitter Arduino or Feather!

Once uploaded you should see the following on the serial console

Now open up another instance of the Arduino IDE - this is so you can see the serial console output from the TX device while you set up the RX device.

Basic receiver example code

This code will receive and reply with a small packet of data.

Open up the example RadioHead→feather→RadioHead69_RawDemo_RX

Load this code into your Receiver Arduino/Feather!

Now open up the Serial console on the receiver, while also checking in on the transmitter's serial console. You should see the receiver is...well, receiving packets

And, on the transmitter side, it is now printing Got Reply after each transmisssion because it got a reply from the receiver

That's pretty much the basics of it! Lets take a look at the examples so you know how to adapt to your own radio network

Radio Freq. Config

Each radio has a frequency that is configurable in software. You can actually tune outside the recommended frequency, but the range won't be good. 900 MHz can be tuned from about 850-950MHz with good performance. 433 MHz radios can be tuned from 400-460 MHz or so.

For all radios they will need to be on the same frequency. If you have a 433MHz radio you will want to stick to 433. If you have a 900 Mhz radio, go with 868 or 915MHz, just make sure all radios are on the same frequency.

Configuring Radio Pinout

At the top of the sketch you can also set the pinout. The radios will use hardware SPI, but you can select any pins for RFM69_CS (an output), RFM_IRQ (an input) and RFM_RST (an output). RFM_RST is manually used to reset the radio at the beginning of the sketch. RFM_IRQ must be an interrupt-capable pin. Check your board to determine which pins you can use!

Also, an LED is defined.

For example, here is the Feather 32u4 pinout:

If you're using a Feather M0, the pinout is slightly different:

And for Feather RP2040:

If you're using an Arduino UNO or compatible, we recommend:

If you're using a FeatherWing or different setup, you'll have to set up the #define statements to match your wiring

You can then instantiate the radio object with our custom pin numbers. Note that the IRQ is defined by the IRQ pin not number (sometimes they differ).

Setup

We begin by setting up the serial console and hard-resetting the RFM69

If you are using a board with 'native USB' make sure the while (!Serial) line is commented out if you are not tethering to a computer, as it will cause the microcontroller to halt until a USB connection is made!

Initializing Radio

Once initialized, you can set up the frequency, transmission power, radio type and encryption key.

For the frequency, we set it already at the top of the sketch

For transmission power you can select from 14 to 20 dBi. Lower numbers use less power, but have less range. The second argument to the function is whether it is an HCW type radio, with extra amplifier. This should always be set to true!

Finally, if you are encrypting data transmission, set up the encryption key

Basic Transmission Code

If you are using the transmitter, this code will wait 1 second, then transmit a packet with "Hello World #" and an incrementing packet number, then check for a reply

Its pretty simple, the delay does the waiting, you can replace that with low power sleep code. Then it generates the packet and appends a number that increases every tx. Then it simply calls send() waitPacketSent() to wait until is is done transmitting.

It will then wait up to 500 milliseconds for a reply from the receiver with waitAvailableTimeout(500). If there is a reply, it will print it out. If not, it will complain nothing was received. Either way the transmitter will continue the loop and sleep for a second until the next TX.

Basic Receiver Code

The Receiver has the same exact setup code, but the loop is different

Instead of transmitting, it is constantly checking if there's any data packets that have been received. available() will return true if a packet with the proper encryption has been received. If so, the receiver prints it out.

It also prints out the RSSI which is the receiver signal strength indicator. This number will range from about -15 to -80. The larger the number (-15 being the highest you'll likely see) the stronger the signal.

If the data contains the text "Hello World" it will also reply to the packet.

Once done it will continue waiting for a new packet

Basic Receiver/Transmitter Demo w/OLED

OK once you have that going you can try this example, RadioHead69_RawDemoTXRX_OLED. We're using the Feather with an OLED wing but in theory you can run the code without the OLED and connect three buttons to GPIO #9, 6, and 5 on the Feathers. Upload the same code to each Feather. When you press buttons on one Feather they will be printed out on the other one, and vice versa. Very handy for testing bi-directional communication!

This demo code shows how you can listen for packets and also check for button presses (or sensor data or whatever you like) and send them back and forth between the two radios!

Addressed RX and TX Demo

OK so the basic demo is well and good but you have to do a lot of management of the connection to make sure packets were received. Instead of manually sending acknowledgements, you can have the RFM69 and library do it for you! Thus the Reliable Datagram part of the RadioHead library.

Load up the RadioHead69_AddrDemo_RX and RadioHead69_AddrDemo_TX sketches to each of your boards

This example lets you have many 'client' RFM69's all sending data to one 'server'

Each client can have its own address set, as well as the server address. See this code at the beginning:

For each client, have a unique MY_ADDRESS. Then pick one server that will be address #1

Once you upload the code to a client, you'll see the following in the serial console:

Because the data is being sent to address #1, but #1 is not acknowledging that data.

If you have the server running, with no clients, it will sit quietly:

Turn on the client and you'll see acknowledged packets!

And the server is also pretty happy

The secret sauce is the addition of this new object:

Which as you can see, is the manager for the RFM69. In setup() you'll need to init it, although you still configure the underlying rfm69 like before:

And when transmitting, use sendToWait which will wait for an ack from the recepient (at DEST_ADDRESS)

on the 'other side' use the recvFromAck which will receive and acknowledge a packet

That function will wait forever. If you'd like to timeout while waiting for a packet, use recvfromAckTimeout which will wait an indicated # of milliseconds

Datasheets & Files

• FCC Test Report
• RoHS Test Report
• RoHS Test Report
• REACH Test Report
• RFM69HCW datasheet - contains the SX1231 datasheet plus details about the module
• SX1231 Transceiver Datasheet

• EagleCAD PCB Files on GitHub
• Fritzing object in Adafruit Fritzing Library
• PDF for Feather 32u4 RFM69 Board Diagram on GitHub
• PDF for Feather 32u4 RFM9x LoRa Board Diagram on GitHub

Schematic

Fabrication Print

Dimensions in Inches