You will need the Adafruit IO Arduino library installed to compile the example sketch. The easiest way to install the library is by using the Arduino IDE v.1.6.4+ Library Manager, and searching for Adafruit IO Arduino.

You will also need to have the ESP8266 Arduino board package installed. For more info about installing the ESP8266 package, visit the HUZZAH ESP8266 setup guide.

Ensure the board package used for the HUZZAH ESP8266 is >= version 2.4.0, older versions have an issue with waking from DeepSleep.

Use the package index URL above to get the latest version of the ESP8266 package.

You must have your Adafruit IO account set up first before you try to connect!

Arduino Sketch

The Arduino sketch for this project is fairly straight forward. We'll be using the IFTT Door Detector sketch for this guide. Make sure to download both the sketch (IFTTT_Door_Detector.ino) and the configuration file (config.h).

Configuring Adafruit IO and WiFi

To configure your ESP8266 with your Adafruit IO account, you will need to set up your IO_USERNAME and IO_KEY in the config.h tab.

To find your IO_USERNAME, navigate to your profile on Adafruit IO and click View AIO Key. Copy the Username field (ctrl+c or command+c)

Then, in the config.h tab, replace the "your_username" text with your the username from your profile:

To find your IO_Key, navigate to your profile, click View AIO Key, and copy the ACTIVE KEY field to your clipboard (ctrl+c or command+c).

In config.h, replace the IO_KEY with the IO Key copied to your clipboard.

Next, we're going to configure the sketch to use your WiFi network. In the config.h tab, replace "your_ssid" with your WiFi's SSID and "your_pass" with your WiFi's password:


By default, the sketch sends the battery level to Adafruit IO once every 5 minutes, and checks the state of the door once every 3 seconds. You can modify these intervals by changing the BATTERY_INTERVAL and SLEEP_LENGTH constants. Setting these constants to lower intervals will result in reduced battery life.


#define SLEEP_LENGTH 3

The bulk of the work for this example happens in the setup() function. The sketch restarts into setup() after it wakes from sleep, so the main loop() never runs.

void setup() {

  // start the serial connection

  while (!Serial);
  Serial.println("AdafruitIO Door Detector");


  // get the current count position from eeprom
  byte battery_count =;

  // we only need this to happen once every X minutes,
  // so we use eeprom to track the count between resets.
  if(battery_count >= ((BATTERY_INTERVAL * 60) / SLEEP_LENGTH)) {
    // reset counter
    battery_count = 0;
    // report battery level to Adafruit IO
  } else {
    // increment counter

  // save the current count
  EEPROM.write(0, battery_count);

  // if door isn't open, we don't need to send anything
  if(digitalRead(DOOR) == LOW) {
    Serial.println("Door closed");
    // we don't do anything
  } else {
    // the door is open if we have reached here,
    // so we should send a value to Adafruit IO.
    Serial.println("Door is open!");

  // we are done here. go back to sleep.
  ESP.deepSleep(SLEEP_LENGTH * 1000000);

The code that connects and sends the state of the door to Adafruit IO can be found within the door_open() function. 

void door_open(){

  // grab the door feed
  AdafruitIO_Feed *door = io.feed("door");

  Serial.println("Sending door value to feed..");

The HUZZAH 8266's battery level is sent the Adafruit IO battery feed once every five minutes. If you want to increase or decrease this interval, you can edit the BATTERY_INTERVAL constant. Be warned, though, decreasing the number will decrease your HUZZAH's battery life. 

void battery_level() {

  // read the battery level from the ESP8266 analog in pin.
  // analog read level is 10 bit 0-1023 (0V-1V).
  // our 1M & 220K voltage divider takes the max
  // lipo value of 4.2V and drops it to 0.758V max.
  // this means our min analog read value should be 580 (3.14V)
  // and the max analog read value should be 774 (4.2V).
  int level = analogRead(A0);

  // convert battery level to percent
  level = map(level, 580, 774, 0, 100);
  Serial.print("Battery level: "); Serial.print(level); Serial.println("%");

  // grab the battery feed
  AdafruitIO_Feed *battery = io.feed("battery");
  // send battery level to AIO

Upload and Test

OK now that you have everything wired up, and your Adafruit IO account set up, upload the above sketch to your HUZZAH ESP8266 board via the FTDI cable or another serial connection.

After uploading, open up the serial port. You should see a long stream of text that looks like this:

What you're seeing is the HUZZAH reading the sensor (Door closed and Door is open!) and then going to sleep (the zzz text indicates its about to go into sleep mode. When the ESP8266 goes to sleep, it resets the board, and so the weird text after the 'zzz' is the reset debug string. Its normal but some terminal programs print it out a little differently.

This program only pushes data to the feed when the door is open, since that's a rare event. So when the door is closed, nothing 'happens'. When you remove the magnet half from the sensor half, you'll get that text that says the door is open, and it will connect to WiFi and update your feed

Log into your Adafruit IO account and look at the door feed to see the messages as they are logged!

After the board is active for five minutes, you'll also see the board measure the battery voltage and upload that to the separate battery feed.

This guide was first published on Oct 19, 2015. It was last updated on Mar 08, 2024.

This page (Arduino Code) was last updated on Mar 08, 2024.

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