Central part of thermostat is an ATmega8 microcontroller, on which are connected two 7-segment 3-digit LED displays, potentiometer, thermoresistor, a coil relay and a push button. 7-segment displays show current air temperature and the desired temperature. Current air temperature is measured by thermoresistor, and potentiometer is used to set the desired temeperature. Coil relay is used as a switch for the boiler, which works on 220 volts. With a push button it is possible to set a time delay when heating of the house will begin.
This is a central heating system thermostat that I have made. It switches central heating system boiler on and off in order to maintain the air temperature on a desired level.
Digits on a 8-segment LED displays are time multiplexed. At one moment only one digit is being lit for a short period, before moving to next digit.
Components are soldered on a stripboard pcb.
The final assembly is put in an old bi-metal thermostat case.
Project source code is available on https://github.com/matijaspanic/electronic-thermostat
Tags: ATmega8 AVR