FAN BUS Controller

The Fan controller part if the project is now up and running. I've decided to use a EPOT as a voltage divider with the output going to a TIP31C (NPN power transistor). The results are actually quite good even if the output isn't linear.
The transistor does get quite warm (ambient + 30c) without a heatsink, but that's not too bad. OK so here it is the ciruit:-

And here's a chart showing the voltage against output.

With abit of code on the Mega8 (PID Controller) I'm now able to control the temperature of a block of metal with a heater mounted on it to within about 0.5c. Here's a chart of the temperature/setpoint. Note how that the temperature changes when the setpoint changes.

part 5 - Reservoir