Make a directory inside your “tessel-code” folder called “relay”, change directory into that folder, and initialize a tessel project:

mkdir relay; cd relay; t2 init


If you have something to turn on and off with the Relay module, cut the power wire, strip the ends to expose the wire, and insert the two exposed ends into port 1 on the Relay module. (If you don’t have something to plug in at the moment, you can still continue; you won’t see anything turn on or off, but the relay makes an audible clicking noise when it latches.)


Plug the relay module into Tessel port A with the hexagon/icon side down and the electrical components on the top, then plug Tessel into your computer via USB.


Install by typing npm install relay-mono into the command line.


Rename “index.js” to “relay.js” and replace the file’s contents with the following:

// Any copyright is dedicated to the Public Domain.

This relay module demo toggles both relay
channels every two seconds, logging the new
values to the console upon latching.

var tessel = require('tessel');
var relaylib = require('relay-mono');

var relay = relaylib.use(tessel.port['A']);

// Wait for the module to connect
relay.on('ready', function relayReady () {
  console.log('Ready! Toggling relays...');
  setInterval(function toggle() {
    // Toggle relay channel 1
    relay.toggle(1, function toggleOneResult(err) {
      if (err) console.log("Err toggling 1", err);
    // Toggle relay channel 2
    relay.toggle(2, function toggleTwoResult(err) {
      if (err) console.log("Err toggling 2", err);
  }, 2000); // Every 2 seconds (2000ms)

// When a relay channel is set, it emits the 'latch' event
relay.on('latch', function(channel, value) {
  console.log('latch on relay channel ' + channel + ' switched to', value);

Save the file.


In your command line, t2 run relay.js Turn some things on and off with code! This gif shows clap-activated lights which use the ambient and relay modules together.

Bonus: Change the code to toggle only one relay channel, every 10 seconds.


What else can you do with a relay module? Try a community-created project.

Check out GitHub