http://www.rigacci.org/wiki/doku.php/doc/appunti/hardware/raspberrypi_thermostat

This is a do-it-yourself project to make a programmable thermostat with the Raspberry Pi, a credit-card sized computer costing about 35 €. I was frustrated by a low-cost thermostat which has only one daily program with just two temperatures. Time accuracy was of a quarter of an hour and temperature accuracy above one Celsius degree.

So I embarked on this project, whose main features are:

• Programmable with the accuracy of the minute and tenths of a degree.
• Can keep several weekly programs, plus MANUAL OFF and MANUAL ON modes.
• Show current status via an LCD.
• Just one push button to cycle through all the programs.
• Talks with the boiler with a ON/OFF relay (which controls the burner status).
• Remote operation and alerting messages via Telegram Messenger chat.
• Remote operation using a web page.
• Extensive graphing capabilities via SNMP.

This is the list of the hardware required, with their cost:

• Raspberry Pi model B with power supply (44 €)
• Dallas DS18B20 temperature sensor (2 €)
• Relay board with two realys, but used just one (3.50 €)
• Push button (1 €)
• LCD display (Nokia 5110-3310) (5 €)
• Edimax WiFi nano USB adapter (10 €)

At the total of 65.50 € you must add a suitable case.

You can define several weekly programs and cycle among them pushing a button. There is a very basic web interface to manage the thermostat remotely, but the preferred way to talk to the thermostat is via Telegram Messenger chat.

The Python daemon which polls the temperature sensor and sets the relay status (ON/OFF) accordingly to a temperature program.

The Telegram Bot which send and receive messages to manage the thermostat remotely. It is written in Python using the telepot library.