Building the thermostat

We are now going to see how to build the code for the thermostat, which will run on your Raspberry Pi Zero board. As the code is quite long, I will only highlight the most important parts here, but you can of course find the complete code inside this book's GitHub repository.

Start by importing the required modules:

var sensorLib = require('node-dht-sensor');
var express = require('express');

Then, we create an Express app, which will allow us to easily structure our application:

var app = express();

Next, we define some variables that are important for our thermostat:

var targetTemperature = 25;
var threshold = 1;
var heaterPin = 29;

The threshold is here so the thermostat doesn't constantly switch between the on and off states when it is near the target temperature. A lower threshold means that you will have a temperature closer to what you want, but also that the heater will switch more frequently.

After that, we are going to define the routes...