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Exercise 2.2 - Sensors

f) Traffic light warning system

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

Enter warning and critical thresholds for the temperature and press "Set thresholds". When the critical threshold is exceeded, the LED will turn red and the hardware button starts blinking. The user needs to act by pressing the button.

Warning threshold:

Critical threshold:

script.js

This is the JavaScript code behind the above application.

/* global log, getInput, tf */
log("Solution for exercise 2.2 f) Traffic light warning system");
// Create a global variable to store the found devices
var devices;
var temperatureSensor;
var led;
var btn;
// Global variable to remember whether action was taken
var temperatureExceededCritical = false;
// Create a global variable for the temperatur threshold
// Set initial threshold to 25° C
var temperatureThresholdWarning = 25;
var temperatureThresholdCritical = 28;
// Initialite connected devices
tf.initDevices(initDone);
// Call this when all connections are established
function initDone(connectedDevices) {
if (connectedDevices.length === 0) {
 log("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();
// Get the RGB LED button and turn it off
 btn = devices.getDeviceByIdentifier(282);
 btn.off();
// Get notified when button is pressed
 btn.registerListener(buttonChanged);
}
function setThresholds() {
 temperatureThresholdWarning = getInput("temperatureThresholdWarning");
 temperatureThresholdCritical = getInput("temperatureThresholdCritical");
 log("New thresholds: Warning: " + temperatureThresholdWarning + ", Critical: " + temperatureThresholdCritical);
}
// This function is the callback for when the button is PRESSED or RELEASED
function buttonChanged(event) {
 var btnState = event.getValue();
if (btnState === "RELEASED") {
 // Turn the button off
 btn.off();
 }
}
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 critical threshold is exceeded
 if (temperature >= temperatureThresholdCritical * 100) {
if (!temperatureExceededCritical) {
log("Warning: Temperature critical threshold exceeded: " + temperatureFormatted);
// Make the hardware button start blinking white
 btn.blink(255, 255, 255, 500);
// 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-warning");
 displayElement.parentElement.classList.add("alert-danger");
 }
// Remember that the temperature is exceeded
 temperatureExceededCritical = true;
}
 // Check if the warning threshold is exceeded
 else if (temperature >= temperatureThresholdWarning * 100) {
log("Warning: Temperature warning threshold exceeded: " + temperatureFormatted);
// Set LED to yellow
 led.setColor(255, 255, 0);
// Make the display's background orange
 displayElement.parentElement.classList.remove("alert-success");
 displayElement.parentElement.classList.remove("alert-danger");
 displayElement.parentElement.classList.add("alert-warning");
// Remember that the temperature is not critical anymore again
 temperatureExceededCritical = false;
 }
 else {
 led.setColor(0, 255, 0);
// Make the display's background green again
 displayElement.parentElement.classList.remove("alert-danger");
 displayElement.parentElement.classList.remove("alert-warning");
 displayElement.parentElement.classList.add("alert-success");
// Remember that the temperature is OK again
 temperatureExceededCritical = false;
 }
}