In this post I will attempt to describe the steps I took to build the arduino based thermostat shown in the following videos. The first video was taken when around just half of the coding of the menu system was complete, but gives you a basic run through of the features.
This second video shows the completed thermostat with additional features implemented over the holidays, which includes a Total Heat Time counter, and a line graphing feature which shows temperature variations over a 24 hour period, including when the heating was turned on, so from the graph you could see how long it takes your heating system to bring the house up to the desired temperature.
Circuit Diagram
Pin Connections
LCD Monitor Video In – 1K resistor to Pin 11
LCD Monitor Video In – 470ohm resistor to Pin 12
LM35 output pin to Analog Pin A1
Button Down to Digital Pin 33
Button Up to Digital Pin 37
Select button to Digital Pin 32
Back button to Digital Pin 36
Relay Coil to PWM Pin 4
1 x Arduino Mega 2560 board (mainly because of the larger memory capacity)
1 x LM35 Temperature Sensor or equivalent
1 x 4 inch LCD Monitor, the one I used was this one from amazon
1 x Maplins Project Box (for housing the arduino and cabling)
1 x 5V Voltage Regulator (I’m using a TS7805)
2 x 1uf Capacitors (for the regulator circuit)
4 x Stateless push buttons
4 x 10K Resistors
1 x 12V power supply (I’m using an old Linksys router power supply rated at 12v @ 1amp)
1 x 6v Relay (with the contacts rated at 240v 3amps or greater for connection to combi boiler)
1 x 1K Resistor (for connection to the Composite input of the LCD monitor – SYNC)
1 x 470 OHM Resistor (for connection to the Composite input of the LCD Monitor – VIDEO)
1 x 3v LED (optional mainly for diagnosing when the relay turns on and off)
For more detail: Build a fully featured Arduino Thermostat
