Overview

This guide is part of a series of guides that cover the basics of using Adafruit IO. It will show you how to send analog values to Adafruit IO from a photocell.

If you haven't worked your way through the Adafruit IO feed and dashboard basics guides, you should do that before continuing with this guide so you have a basic understanding of Adafruit IO.

You should go through the setup guides associated with your selected set of hardware, and make sure you have internet connectivity with the device before continuing. The following links will take you to the guides for your selected platform.

If you have went through all of the prerequisites for your selected hardware, you are now ready to move on to the Adafruit IO setup steps that are common between all of the hardware choices for this project. Let's get started!

Adafruit IO Setup

The first thing you will need to do is to login to Adafruit IO and visit the Settings page.

Click the VIEW AIO KEY button to retrieve your key.

A window will pop up with your Adafruit IO. Keep a copy of this in a safe place. We'll need it later.

Creating the Analog Feed

Next, you will need to create a feed called Analog. If you need help getting started with creating feeds on Adafruit IO, check out the Adafruit IO Feed Basics guide.

Adding the Gauge Block

Next, add a new Gauge block to a new or existing dashboard. Name the block whatever you would like, and give it a max value of 1024 and a min value of 0. Make sure you have selected the Analog feed as the data source for the gauge.

If you need help getting started with Dashboards on Adafruit IO, check out the Adafruit IO Dashboard Basics guide.

When you are finished editing the form, click Create Block to add the new block to the dashboard.

Next, we will look at wiring the circuit.

Wiring

Arduino Wiring

You will need the following parts for this tutorial:

  • 1x Adafruit IO compatible Feather
  • 3x jumper wires
  • 1x 10k resistor
  • 1x photocell

You will need to connect the following pins to the photocell and 10k resistor:

  • Feather GND to one leg of the 10k resistor
  • The second leg of the 10k resistor to one leg of the photocell
  • Feather A0 (or ADC) to the same leg of the photocell as the 10k resistor.
  • Feather 3V to the second leg of the photocell

Note: Resistors and photocells are not polarized, so they can be connected to the circuit in either direction.

Arduino Setup

You should go through the setup guides associated with your selected set of hardware, and make sure you have internet connectivity with the device before continuing. The following links will take you to the guides for your selected platform.

You will need to make sure you have at least version 2.3.0 of the Adafruit IO Arduino library installed before continuing.

For this example, you will need to open the adafruitio_08_analog_in example in the Adafruit IO Arduino library.

Next, we will look at the network configuration options in the sketch.

Arduino Network Config

To configure the network settings, click on the config.h tab in the sketch. You will need to set your Adafruit IO username in the IO_USERNAME define, and your Adafruit IO key in the IO_KEY define.

WiFi Config

WiFi is enabled by default in config.h so if you are using one of the supported WiFi boards, you will only need to modify the WIFI_SSID and WIFI_PASS options in the config.h tab.

FONA Config

If you wish to use the FONA 32u4 Feather to connect to Adafruit IO, you will need to first comment out the WiFi support in config.h

Next, remove the comments from both of the FONA config lines in the FONA section of config.h to enable FONA support.

Ethernet Config

If you wish to use the Ethernet Wing to connect to Adafruit IO, you will need to first comment out the WiFi support in config.h

Next, remove the comments from both of the Ethernet config lines in the Ethernet section of config.h to enable Ethernet Wing support.

Next, we will look at how the example sketch works.

Arduino Code

The adafruitio_08_analog_in example uses pin A0 by default on all boards, and that can be modified if needed by changing the PHOTOCELL_PIN define.

Download: file
/************************ Example Starts Here *******************************/

// analog pin 0
#define PHOTOCELL_PIN A0

The next chunk of code sets up two integer variables to track the state of the photocell, and an Adafruit IO Feed instance for a feed called analog.

Download: file
// photocell state
int current = 0;
int last = -1;

// set up the 'analog' feed
AdafruitIO_Feed *analog = io.feed("analog");

The setup function connects your feather to Adafruit IO. The code will wait until you have a valid connection to Adafruit IO before continuing with the sketch. If you have any issues connecting, check config.h for any typos in your username or key.

Download: file
void setup() {

  // start the serial connection
  Serial.begin(115200);

  // wait for serial monitor to open
  while(! Serial);

  // connect to io.adafruit.com
  Serial.print("Connecting to Adafruit IO");
  io.connect();

  // wait for a connection
  while(io.status() < AIO_CONNECTED) {
    Serial.print(".");
    delay(500);
  }

  // we are connected
  Serial.println();
  Serial.println(io.statusText());

}

Next, we have the main loop() function. The first line of the loop function calls io.run(); this line will need to be present at the top of your loop in every sketch. It helps keep your device connected to Adafruit IO, and processes any incoming data.

Download: file
void loop() {

  // io.run(); is required for all sketches.
  // it should always be present at the top of your loop
  // function. it keeps the client connected to
  // io.adafruit.com, and processes any incoming data.
  io.run();

The next chunk of code inside the loop() checks the current value of the photocell, and saves the value of the photocell in the current variable.

We then check if the current photocell value is equal to the last photocell value. If it is equal, we will return early and not continue with the rest of the loop.

Download: file
  // grab the current state of the photocell
  current = analogRead(PHOTOCELL_PIN);

  // return if the value hasn't changed
  if(current == last)
    return;

The final chunk of the loop() function prints the current value to the Arduino Serial Monitor, and sends the current value to the analog feed on Adafruit IO. We also set last = current; so we can tell if the value of the photocell has changed in the next run of the loop.

Download: file
  // save the current state to the analog feed
  Serial.print("sending -> ");
  Serial.println(current);
  analog->save(current);

  // store last photocell state
  last = current;

  // wait one second (1000 milliseconds == 1 second)
  delay(1000);

}

Upload the sketch to your board, and open the Arduino Serial Monitor. Your board should now connect to Adafruit IO.

Download: file
Connecting to Adafruit IO....

Adafruit IO connected.

You can now cover the photocell with your hand, and you should see the changing values being sent to Adafruit IO.

Download: file
sending -> 1024
sending -> 953
sending -> 259
sending -> 476
sending -> 248
sending -> 173
sending -> 224
sending -> 291
sending -> 1024

Check your dashboard on Adafruit IO, and you should see the gauge respond to the changes in photocell values.

Adafruit IO FAQ

Encountering an issue with your Adafruit IO Arduino Project?

If you're having an issue compiling, connecting, or troubleshooting your project, check this page first.

Don't see your issue?  Post up on the Adafruit IO Forum with your issue.

Compiling my sketch returns an error:

error: return-statement with a value, in function returning 'void' [-fpermissive]
virtual void flush() { return iClient->flush(); };

Firmware Beta 2.5.0 for the ESP8266 breaks compatibility with ArduinoHttpClient(which is used by Adafruit IO). The Adafruit IO Arduino library is currently unsupported by this beta firmware. To get it working, we'll downgrade the firmware on the ESP8266 to a stable version.

Launch the Board Manager from Arduino by navigating to Tools -> Boards -> Board Manager. Type ESP8266 into the search bar. From the dropdown, select version 2.4.2

Clicking install will uninstall the 2.5.0-beta and install a stable firmware version.

I encounter the following error when compiling my sketch:

  fatal error: Adafruit_MQTT.h: No such file or directory, #include "Adafruit_MQTT.h"

The Adafruit IO Arduino library is dependent on our Adafruit IO MQTT Library.

To resolve this error, from the Arduino IDE, navigate to the Manage Libraries... option in the Sketch -> Include Library menu.

To resolve this error, from the Arduino IDE, navigate to the Manage Libraries... option in the Sketch -> Include Library menu.

My Serial Monitor prints "..." endlessly after the "Connecting to Adafruit IO" message

Your board is not connecting to Adafruit IO, but why? Let's find out:

First, check in config.h that you have the correct IO_USERNAMEIO_KEYWIFI_SSID, and WIFI_PASS are set correctly. 

Next, we're going to modify the while loop which waits for an IO connection in your sketch. Change the line in the status check loop from Serial.println(.);to Serial.println(io.statusText());

// wait for a connection
while(io.status() < AIO_CONNECTED) {
Serial.println(io.statusText());
delay(500);
}

Verify and re-upload the sketch. If you're receiving a Network disconnected error message, the board is not able to talk to the internet. Re-check your hardware, connections, and router settings. 

If it's still not showing Adafruit IO connected, check the IO status on the Adafruit Status page to make sure the service is online.

My data isn't displaying, is Adafruit IO's {service/MQTT/API} down?

Possibly - you can check IO status on the Adafruit Status page

Is my data being sent properly? Am I sending too much data?

There's a monitor page built-into Adafruit IO which provides a live view of incoming data and error messages. Keep this page open while you send data to your Adafruit IO devices to monitor data and errors. 

This guide was first published on Feb 16, 2017. It was last updated on Feb 16, 2017.