Last month, during the Azure Bootcamp, I was introduced in programming the Tessel.

This device is a fairly cheap IoT programming board and for me, the most remarkable feature was that it was running on JavaScript.


Yes, everybody with the basic understanding of JavaScript can start programming the Tessel.

My main goal for  that day was putting some effort in Azure EventHubs but first I did the ‘hello world’ of the Tessel called Blinky.js

// Import the interface to Tessel hardware
var tessel = require('tessel');
// Set the led pins as outputs with initial states
// Truthy initial state sets the pin high
// Falsy sets it low.
var led1 = tessel.led[0].output(1);
var led2 = tessel.led[1].output(0);
setInterval(function () {
  console.log("I'm blinking! (Press CTRL + C to stop)");
  // Toggle the led states
}, 100);

It was not that intuitive to get this working (I had to install node.js etc) but the convenience of JavaScript is very nice. So just follow the scripted examples.

Then I tried out and combined two other hands-on labs:

These HOLs helped me to explore how I can send messages to the EventHub. And I was surprised how easy it was to send JSON data into the EventHub. And now I can imagine how the EventHub is just a VERY BIG bucket in which Azure MessageBus messages are off-loaded. And I can image how the data can be investigated by StreamInsight for a couple of days before the data gets steel and is deleted.

So finally, just for fun, I came up with this continuous probing and sending:

var https = require('https');
var crypto = require('crypto');
var climatelib = require('climate-si7020');
var tessel = require('tessel');
var climate = climatelib.use(tessel.port['A']);

climate.on('ready', function () {
  console.log('Connected to si7005');

climate.on('error', function(err) {
  console.log('error connecting module', err);

// Event Hubs parameters
console.log('Please ensure that you have modified the values for: namespace, hubname, partitionKey, eventHubAccessKeyName');
console.log('Please ensure that you have created a Shared Access Signature Token and you are using it in the code')

var namespace = 'SvdvEh-ns';
var hubname ='svdveh';
var deviceName = 'mytessel';
var eventHubAccessKeyName = 'SendRights';
var createdSAS = 'SharedAccessSignature sr=[...]';

console.log('Namespace: ' + namespace);
console.log('hubname: ' + hubname);
console.log('publisher: ' + deviceName);
console.log('eventHubAccessKeyName: ' + eventHubAccessKeyName);
console.log('SAS Token: ' + createdSAS);

var SendItem = function(payloadToSend){
  // Send the request to the Event Hub
  var options = {
    hostname: namespace + '',
    port: 443,
    path: '/' + hubname + '/publishers/' + deviceName + '/messages',
    method: 'POST',
    headers: {
      'Authorization': createdSAS,
      'Content-Length': payloadToSend.length,
      'Content-Type': 'application/atom+xml;type=entry;charset=utf-8'

  var req = https.request(options, function(res) {
    console.log("statusCode: ", res.statusCode);
    res.on('data', function(d) {

  req.on('error', function(e) {


setImmediate(function loop () {
  climate.readTemperature('f', function (err, temp) {
    climate.readHumidity(function (err, humid) {
      console.log('Degrees:', temp.toFixed(4) + 'F', 'Humidity:', humid.toFixed(4) + '%RH');
      var payload = '{\"Temperature\":\"'+temp.toFixed(4)+'\",\"Humidity\":\"'+humid.toFixed(4)+'\"}';
      setTimeout(loop, 5000);

This code was enough to see how the EventHub was filled with data. I had no time to check out StreamInsight. But it seems very easy to write some SQL-like code to get the right information out of the hubs.

The biggest problem was the administration of all the namespaces, keys, connection strings and secrets of both the MessageBus and the EventHub. Sometimes I had to cut/copy/paste parts of connection strings but that was not that intuitive.

And the Tessel? It was real fun to play with. And the complete humidity/temperature sensor was easy to plug in (had to fix the code because it was referencing another module type). But somehow I missed the spider web of wires and components and the accidental reboots of the RaspberryPi 🙂

A special mention goes to the free service bus explorer. It was very exciting to see messages coming in live. Very useful for debugging too.