Raspberry Pi central heating controller

Now the solar monitoring and logging system is working we are going to build the wireless remote control for the hot water and central heating boiler and controller/programmer.

We currently have a variant of an ACL Drayton Lifestyle LP522 5DAY/ 2DAY electronic central heating programmer which is an older design but reliable and has been in use in the house for over 10 years.  

I was able to source a boxed new (1998 model) from eBay and proceeded to trace the tracks on the PCB to see if it was possible to add remote triggering and monitoring of the programmer's relays via a PIC processor which takes and sends commands via an XBee wireless module which is paired with an XBee module on the Raspberry Pi.

The photo below shows the PCB on the programmer with the PCB tracks marked in different colours to show functionality.

The 240v mains supply comes in via the first two pins across the top and the other 4 pins are for the relay outputs which connect to the central heating system.

Key to line colours:
Red: 4.5V supply
Black: Ground supply
Purple: Relay supply
Orange: Relay supply
Blue: Relay activation which is ground-switched via microcontroller
Yellow: Relay activation which is ground-switched via microcontroller

Once we had found suitable activation points on the board which we can use we proceeded to build some simple level buffers and adapters for the XBee module so it could be used in a breadboard. This was connected to a MikroElektronika easypic 6 development board and a pic16f628a chip. The second XBee was connected to a Sparkfun USB board and this was connected to a PC and used Putty to talk via the COM port.

We wrote some initial test code to check for connectivity and have been able to turn LEDs on and off on the dev board and also send the text back to the PC when buttons are pressed.

The next stage is to write the full functionality required to activate the boiler systems and also monitor the status, once that is complete build a new PCB to hopefully go inside the central heating controller.

On the Raspberry Pi we are planning to build a web-based front end to administer a MySql database which has the on and off times for the hot water and boiler and also have a cron job which runs every few minutes to check the database and activates the boiler if required. I will be adding the code and progress to the blog as each part is built.