Skill Dev V - Wei, Sue, and Xiaoran

Made by Wei Liang, Xuyang Jin and Xiaoran Zhang

Created: December 18th, 2020



The idea of this lab to build communications between two paired Particle devices.

The mechanism is as follows:

Each device will have a loop to test if the button is pushed. If it is, then the device will send out a unique event with its device name.

Each device will also listen to the event sent by other devices. If they received the event name that they subscribed to, they will turn on their fan to respond.

Nut in a shell: Press the button of one device will turn on the fan of the other device.



The circuit and the code are shown below. The circuit of each device is identical. The code is revised from the template from the course website.

// This value will store the last time we published an event
long lastPublishedAt = 0;
// this is the time delay before we should publish a new event
// from this device
int publishAfter = 10000;

bool shouldActivate = false;

int solPin = D4;

int buttonPin = D2;

void setup()

  // We'll want to subscribe to an event thats fairly unique

  // From the Particle Docs
  // A subscription works like a prefix filter.
  // If you subscribe to "foo", you will receive any event
  // whose name begins with "foo", including "foo", "fool",
  // "foobar", and "food/indian/sweet-curry-beans".

  // Basically this will match any event that starts with 'db2018/paired/'
  // This is a feature we'll useto figure out if our event comes from
  // this device or another (see publishMyEvent below)

  Particle.subscribe(  "diot/2020/paired/" , handleSharedEvent );
  pinMode(solPin, OUTPUT);
  pinMode(buttonPin , INPUT_PULLUP); // sets pin as input


void loop()
    // publish my event
    // you'll want some more complex stuff here
    int buttonState = digitalRead( buttonPin );

    // when the button is not pushed we'll get a HIGH
    // if LOW, send the event

    if( buttonState == LOW )
        // turn the LED On
    // delay for a bit

void publishMyEvent()
  // Remember that a device can publish at rate of about 1 event/sec,
  // with bursts of up to 4 allowed in 1 second.
  // Back to back burst of 4 messages will take 4 seconds to recover.
  // So we want to limit the amount of publish events that happen.

  // check that it's been 10 secondds since our last publish
  if( lastPublishedAt + publishAfter < millis() )
      // Remember our subscribe is matching  "db2018/paired/"
      // We'll append the device id to get more specific
      // about where the event came from

      // System.deviceID() provides an easy way to extract the device
      // ID of your device. It returns a String object of the device ID,
      // which is used to identify your device.

      String eventName = "diot/2020/paired/" + System.deviceID();

      // now we have something like "diot/2019/paired/0123456789abcdef"
      // and that corresponds to this devices info

      // then we share it out
      Particle.publish( eventName, "data goes here" );

      // And this will get shared out to all devices using this code

      // we just pubished so capture this.
      lastPublishedAt = millis();


// Our event handlde requires two bits of information
// This gives us:
// A character array that consists of the event name
// A character array that contains the data published in the event we're responding to.
void handleSharedEvent(const char *event, const char *data)
    // Now we're getting ALL events published using "db2018/paired/"
    // This includes events from this device.
    // So we need to ignore any events that we sent.

    // Let's check the event name
    String eventName = String( event ); // convert to a string object
    // This gives us access to a bunch of built in methods
    // Like indexOf()
    // Locates a character or String within another String.
    // By default, searches from the beginning of the String,
    // but can also start from a given index,
    // allowing for the locating of all instances of the character or String.
    // It Returns: The index of val within the String, or -1 if not found.

    // We can use this to check if our event name contains the
    // id of this device

    String deviceID = System.deviceID();

    // device id = 0123456789abcdef
    // event = "diot/2019/paired/0123456789abcdef"

    if( eventName.indexOf( deviceID ) != -1 ){
      // if we get anything other than -1
      // the event came from this device.
      // so stop doing stuff

    // otherwise do your stuff to respond to
    // the paired device here

    shouldActivate = true;
    if( shouldActivate ){
        doSolenoid(  );
        shouldActivate = false;



void doSolenoid(  ){
    digitalWrite(solPin, HIGH);
    delay( 5000 ) ;
    digitalWrite(solPin, LOW);
    delay( 100 );
Click to Expand


Below is the demo video.

Skill Dev V
Wei Liang -


This lab is a preliminary requirement for the final project since we need communications between devices. After finishing this lab, we have a general idea about how particle devices talk to each other. The instructions on the course website are very detailed and easy to follow so the lab went smoothly.