<< Back

Exercise 2.2 - Sensors

c) Temperature warnings with threshold

This is the console. All output created with writeLog() is shown here.

Enter a threshold for the temperature and press "Set threshold". When the threshold is exceeded, the LED will turn red.

script.js

This is the JavaScript code behind the above application.

/* global log, getInput, tf */
writeLog("Solution for exercise 2.2 c) Temperature warnings with threshold");
// Create a global variable to store the found devices
var devices;
var temperatureSensor;
var led;
// Create a global variable for the temperatur threshold
// Set initial threshold to 25° C
var temperatureThreshold = 25;
// Initialite connected devices
tf.initDevices(initDone);
// Call this when all connections are established
function initDone(connectedDevices) {
if (connectedDevices.length === 0) {
 writeLog("Oops, didn't find any devices! Make sure they are connected and refresh this page!");
 }
// Store the devices on the global variable
 devices = connectedDevices;
// Get the humidty sensor (includes temperature)
 temperatureSensor = devices.getDeviceByIdentifier(283);
// Get notified about temperatures changes
 temperatureSensor.registerListener(temperatureOrHumidityChanged);
// Get the RGB LED
 led = devices.getDeviceByIdentifier(271);
// Set the LED off on startup
 led.off();
}
function setThreshold() {
 temperatureThreshold = getInput("temperatureThreshold");
 writeLog("New threshold: " + temperatureThreshold);
}
function temperatureOrHumidityChanged(event) {
var temperature = event.getValue("temperature");
// Do nothing if this is not a temperature update (but rather humidity)
 if (temperature == null) {
 return;
 }
// Format the temperature and add unit
 let temperatureFormatted = (temperature / 100).toFixed(2) + "° C";
// Get the display element from the HTML via its ID
 var displayElement = document.getElementById("temperatureDisplay");
// Update the temperature display
 displayElement.textContent = temperatureFormatted;
// Check if the threshold is exceeded
 if (temperature >= temperatureThreshold * 100) {
 writeLog("Warning: Temperature threshold exceeded: " + temperatureFormatted);
// Set LED to red
 led.setColor(255, 0, 0);
// Make the display's background red
 displayElement.parentElement.classList.remove("alert-success");
 displayElement.parentElement.classList.add("alert-danger");
 }
 else {
 led.off();
// Make the display's background green again
 displayElement.parentElement.classList.remove("alert-danger");
 displayElement.parentElement.classList.add("alert-success");
 }
}