As I've been experimenting with the BeagleBone Blue I decided it would make sense to do a bit of coding with Node.JS rather than Python as I've used for a few previous project. I also wanted to see if I could connect it up to MQTT as I planned to use that for another project.
Node.js is a platform built on Chrome's JavaScript runtime for easily building fast and scalable network applications. Node.js uses an event-driven, non-blocking I/O model that makes it lightweight and efficient, perfect for data-intensive real-time applications that run across distributed devices.
MQTT stands for MQ Telemetry Transport. It is a publish/subscribe, extremely simple and lightweight messaging protocol, designed for constrained devices and low-bandwidth, high-latency or unreliable networks. The design principles are to minimise network bandwidth and device resource requirements whilst also attempting to ensure reliability and some degree of assurance of delivery. These principles also turn out to make the protocol ideal of the emerging “machine-to-machine” (M2M) or “Internet of Things” world of connected devices, and for mobile applications where bandwidth and battery power are at a premium.
My first simple project to combine those two was to hook up to Cayenne, an IOT dashboard from myDevices. The dashboard allows you to add various widgets for displaying values, voltages, temperatures etc and to log their values over time. There are also triggers that allow you to notify people if certain limits are exceeded for example your beer brewing temperature monitor goes above a particular temperature.
The dashboard supports Raspberry Pi and Arudino boards out of the box and there's a growing list of other supported hardware. However, as my device was not on the list it meant I'd have to use the bring-your-own-thing-api this allows you to connect upto to the MQTT directly and publish and subscribe to channels to interact with the dashboard.
When using the API you create a new device in the dashboard and it will let you know the username, password and clientID which then must be used with all further connections. It's best to put these into a separate configuration file but I've just added mine to the top of the script as variables. Here's where there's a bit of a chicken and egg situation as you can't continue building the dashboard until the app has connected at least once.
To run the following you can install MQTT using NPM.
var mqtt = require('mqtt')
var data = 1;
console.log('Connecting to Queue');
var apiVersion = "v1";
var username = '123456789012345678901234567890';
var clientId = '123456789012345678901234567890';
var password = '123456789012345678901234567890';
var rootTopic = [
apiVersion,
username,
'things',
clientId
].join('/');
var client = mqtt.connect('mqtt://mqtt.mydevices.com',{
port: 1883,
clientId: clientId,
username: username,
password: password,
connectTimeout: 5000
});
client.on('connect', function () {
console.log('Connected');
client.subscribe(rootTopic + '/cmd/+');
client.publish(rootTopic + '/sys/model', 'Node Test');
client.publish(rootTopic + '/sys/version', 'V1');
})
client.on('message', function (topic, message) {
const payload = message.toString().split(',');
const topics = topic.toString().split('/');
const seq = payload[0];
const cmd = payload[1];
const channel = topics[5];
console.log(channel + "-" + cmd);
client.publish(rootTopic + '/data/' + channel, cmd); //Echo value back
client.publish(rootTopic + '/response', 'ok,'+seq);
})
client.on('close', function (message) {
console.log('closed');
console.log(message);
client.end(); })
client.on('error', function (message) {
console.log('error occurred');
console.log(message);
client.end(); })
client.on('disconnect', function () {
console.log('disconnection occurred');
client.end(); })
function writeData() {
var topic = rootTopic + '/data/testChannel';
var payload = data.toString();
client.publish(topic, payload);
data = data + 1;
}
process.on('SIGINT', function () {
console.log("Shutting down SIGINT (Ctrl-C)");
client.end();
process.exit();
})
function loop() {
console.log("Heartbeat...");
writeData();
};
function run() {
console.log('Running');
setInterval(loop, 30000);
};
run();
The app above is designed to publish a value to channel "testChannel" this simply increments each time the loop code runs.
The switch setting is a little more complex. It works by listening for commands "cmd" and when it receives a message it echos the value back again and acknowledges the command with a "response". It's important to do this otherwise the switch widget on the dashboard will become unresponsive. You can "unfreeze" it by editing and saving the settings. It's also important to use distinct channels for your switch and other widgets as that can also affect the behaviour.
Other problems I found was that my firewall blocked connections to the MQTT port by default. The system information does not show up on the dashboard and I felt the dashboard could do with a simple "status" type widget to pass text message back and forth.
I also found that the responsive website for MyDevices made it almost impossible to login in mobile mode and the "App" for Android did not support my custom device. The documentation page is a massive long HTML page with #tags to identify each section. Again this proved challenging when reading on mobile.
So connecting to MQTT in Node is very easy and wiring up to the Cayenne dashboard is straightforward (if not foolproof). The experiment puts me in good stead for my project so for me was a big success.
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