In this prototyping stage, we will develop the Arduino and Python code for our thermostat, which will be later used in the second stage with minor changes. Before you start the coding exercise, make sure that you have the thermostat sensor unit ready with the Arduino board and the connected sensors, as described in the previous section. For this stage, you will be using your regular computer which is equipped with the Arduino IDE and the Python programming environment. The prototyping stage requires two levels of programming, the Arduino sketch for the thermostat sensor unit and the Python code for the computational unit. Let's get started with coding for our thermostat.