A Physical Yo Button

I think we’re all still trying to figure out what Yo’s place is in the internet family but as of right now it’s basically a viral app. As soon as I found out there was an API for it I just knew I had to attach some hardware to it. Here’s a demo of what I put together.

The whole thing took me about 4 hours once I resolved my API issue (I originally gave them the wrong URL for the callback and had to email them to fix it). I want to share the process in case other people want to integrate Yo with hardware.

Proof It Works

How It Works

You send a Yo to UCASTS to subscribe —-> My live yo counter increments —-> Anytime I push the magic button all of my subscribers get a Yo!.

In terms of hardware you can customize this process to do whatever you want.

  1. User subscribes to your Yo feed
  2. A callback allows you to execute some action when someone subscribes
  3. You now have the ability to easily send a Yo to all of your subscribers based on any trigger you can think of.

Understanding the API

To sign up for the API just head over to http://yoapi.justyo.co/. You’ll be walked through a few simple steps to get things set up. If you want notifications when people subscribe you’ll need to specify a callback url that the api can call. Once you’ve finished filling out the form you’ll have to wait for Yo to email you your api token. Mine took overnight but I didn’t register until later in the afternoon.

Once you have your api token all you have to do to send a Yo to all of your subscribers is POST your api token to api.justyo.co/yoall/

curl --data “api_token=[your_api_token]” http://api.justyo.co/yoall/

That’s all there is to it.

The Server

So there are really two parts to this. We need a backend to handle the callback requests from the Yo api and a client running on the Pi to handle our hardware interaction. Let’s start with the server. This is really quite simple. I created an Express website that I pushed to Heroku and then pointed one of my domains to it. In µCast #17 I showed how to set up Socket.IO with Express and that’s all I did here with one change. Because the socket.io server reuses the regular express server I had to define a route in the www file which also meant I had to move the 404 and error handler there. Here’s what I ended up with in www.

#!/usr/bin/env node
var debug = require('debug')('microcasts-tv');
var app = require('../app');
var io = null;

app.set('port', process.env.PORT || 3000);

app.get('/new', function(req, res){
io.emit('yoReceived', req.query.username);

app.post('/new', function(req, res){
io.emit('yoReceived', req.query.username);

/// catch 404 and forward to error handler
app.use(function(req, res, next) {
var err = new Error('Not Found');
err.status = 404;

/// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: err

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
res.status(err.status || 500);
res.render('error', {
message: err.message,
error: {}

var server = app.listen(app.get('port'), function() {
debug('Express server listening on port ' + server.address().port);

io = require('socket.io').listen(server);

So when a request to my callback url happens I simply emit a message to the client running on the Raspberry Pi.

The Pi Client

The client piece of this project was fairly simple given the fact that I already had a display and button wired up on a breadboard and connected to a Pi. The first piece to the client is listening for websocket messages from the server to detect new subscribers. That’s as easy as:

var socket = require("socket.io-client")('http://yo.microcasts.tv');

var yoCount = 0;

socket.on('connect', function(){
console.log("Connected to server");
socket.on('yoReceived', function(username){
// Increment the yo count and update display
updateDisplay(yoCount + "");

I’m using the spi package to connect to my display. I don’t store the count anywhere locally at this point. I just count the Yos I’ve gotten since launching the program but it would be trivial to store that info and track your Yo total. Every time I get a new websocket message I just update the display.

var spi = new SPI.Spi('/dev/spidev0.0');

function updateDisplay(text){
var t = new Buffer(text);
var r = new Buffer(text);
var clearMsg = new Buffer([0x76]);
var clearRx = new Buffer([0x00]);
spi.transfer(clearMsg, clearRx, function(dev, buf){});
spi.transfer(t, r, function(dev, buf){});

The final piece to the client is sending a Yo to all of my followers when I push a button. Since the API is so simple we can accomplish that with just 12 lines of code if we use Requestify:

var gpio18 = gpio.export(24, {direction: 'in', ready: function(){}});

// Listen for button presses
gpio18.on('change', function(value){
if (value === 1){
console.log("You pressed the button");
requestify.post('http://api.justyo.co/yoall/', {
api_token: "[your token]"
console.log("Yo sent to subscribers!");


My one regret with this project was that I didn’t have one of these from Sparkfun on hand:

Image provided by Sparkfun as CC BY-NC-SA 3.0

I create a Gist that has the meat of the code if you’re interested.

Got any ideas on how to integrate hardware with the Yo API? I’d love to here about it.

If this article brought you any value at all I’d really appreciate it if you would share it