| I'm currently working on one. The aim is to have a microcontroller that does several things. One is temperature control, for which I need a thermostat of some sort.
I have opted to use a thermistor as the temperature sensing element. Hook that up to an Analogue to Digital Converter (ADC), a microcontroller, a bit of programming and soldering.... presto. At least thats the plan. So far I've got as far as putting together the thermistor and getting the microcontroller to work out the temperature. I still have a wee way to go.
In a style that is now becomming typical of the way I do things, I have gone for the extreme challenge. You dont need to go that far. You can set up a simple on/off thermostat using a voltage comparitor (a small electronic conponent) a few resistors, diodes and capacitors. There are plenty of free schematics available on the web.
The reason I am doing it the hard way is so that I can put in more complex control methods. On/off is ok, but it leads to cyclic variations in the control variable (in our case the temperature of the tank). in english... it goes up.... it comes down... over and over and over again. I want to see if I can keep it steady.
I do agree with the V man. Its usually easier and more reliable to buy reputable gear when it comes to filtration and temperature control.
__________________
Craig | 
