Monitoring what?

• 
  Light

• 
  Temperature

• 
  Humidity

Temperature sensor TMP36

• Datasheet : TMP3x
• Polarized component
• Output voltage only depend from temperature:

  \(T = 100 * V_{out} - 50\)

Installing Johnny Five

// package.json
{
    "dependencies": {
        "johnny-five": "latest"
    }
}

npm install

Displaying temperature

var five = require('johnny-five');

var board = new five.Board();
var temperatureSensor;

board.on('ready', function() {
    temperatureSensor = new five.Sensor({ pin: 'A0', freq: 1000 });
    temperatureSensor.on('data', function() {
        console.log(getTemperature() + "°C");
    });
});

function getTemperature() {
    var out = temperatureSensor.value * (5 / 1023);
    return Math.round(out * 100 – 50);
}

Smoothing output

• Very low intensity
• Very sensitive to electro-magnetic noise
• Too long wires => unstable output
• Smoothing output with capacitors

Photoresistor SEN-09088

• Datasheet : SEN-09088
• Non linear resistance
• Calibration required

Voltage divider bridge

Ohm's law:
$U = R * I$

Mesh method:
$U = U_{1} + U_{2}$

Voltage divider:
$U_{2} = U * \frac{R_{2}}{R_{2} + R_{1}}$

$R_{2} = \frac{U_{2} * R_{1}}{(U - U_{2})}$

Displaying light

var VOLTAGE = 5;
var LIGHT_DIVIDER_RESISTANCE = 10;

board.on('ready', function() {
    lightSensor = new five.Sensor('A1');
    lightSensor.scale([0, 1023]);

    lightSensor.on('data', function() {
        console.log(getLightResistance() + '%');
    });
});

function getLightResistance() {
    var r  = lightSensor.value * LIGHT_DIVIDER_RESISTANCE;
    r /= (VOLTAGE – lightSensor.value);

    return r;
}

Humidity sensor à la MacGyver

• Voltage proportional to humidity
• Calibration required: dry and wet soil
• Zinc-coated or stainless steel wire
• Compost = chemical reactor

Displaying humidity rate

var HUMIDITY_DRY_RESISTANCE = 150;
var HUMIDITY_WET_RESISTANCE = 10;
var HUMIDITY_DIVIDER_RESISTANCE = 10;

board.on('ready', function() {
    humiditySensor = new five.Sensor({ pin: 'A2', frequency: 2000 });
    humiditySensor.scale([0, VOLTAGE]);

    humiditySensor.on('data', function() {
        console.log(getHumidity() + '%');
    });
});

function getHumidity() {
    var resistance = humiditySensor.value * HUMIDITY_DIVIDER_RESISTANCE / (VOLTAGE - humiditySensor.value);
    var humidityRate = 100 * (HUMIDITY_DRY_RESISTANCE - resistance) / (HUMIDITY_DRY_RESISTANCE - HUMIDITY_WET_RESISTANCE);

    return Math.round(humidityRate);
}

Installing socket.io

// package.json
{
    "dependencies": {
        // ...
        "socket.io": "latest"
    }
}

npm install

Socket.io: server side

var io = require('socket.io').listen(8080);

board.on('ready', function() {
    io.sockets.on('connection', function(socket) {
        console.log('New connection: ' + socket.id);

        tempSensor.on('data', function() {
            socket.emit('temp', getTemperature());
        });
    });
});

Socket.io: client side

<script src="//:8080/socket.io/socket.io.js">
</script>

var socket = io.connect("//:8080");

socket.on("temp", function (value) {
    $(".temperature .value").text(value + "°C");
});