Electrical connections to the fans and making the temperature sensors
To connect the fans together (in parallel), I purchased a piece of PCB strip board (Veroboard as it once was) 95 x 432 mm from Rapid Electronics (part 34-0535) and cut it into four strips, 8 holes wide. I took some strips of right angled headers(Rapid 50-8032) and broke off twenty 3-way pieces.
I pared off the guides on the fan sockets with a Stanley knife blade, plugged in the header then fixed it in position on the strip board with a mini G-clamp. (The black plastic spacers on the headers need to be pushed right up to the right angle so as to make the pins long enough to engage satisfactorily with the plug - or you could remove the spacer entirely once the header was soldered in place.)
Pins poking through to the copper track side of the strip board ready for soldering.
The system needs a temperature sensor for the room and a sensor for the radiator water so the fans do not run when the water is not hot (that is when the central heating is off).
The room sensor will be the same as the sensor for the central heating controller. The water temperature sensor will also user the TMP102 but will need to clamp onto a 15mm radiator supply pipe. (Later, I thought I might have simplified things a bit and used an LM35 analogue sensor connected to an Arduino analog port. I’ve got a sketch of how that could be done here…)
The pictures show some metal work and some stripboard I used to link the RJ45 socket, the 5v to 3.3v level shifter and the TMP102 breakout board. It’s all a bit of a fiddle and a bit inelegant but it works. A plastic protective case would be nice.