Hi everyone.
I'm back with a question about a very simple thermistor circuit project. I am trying to make a circuit that will turn on three 12V fans (computer power supply fans) when the temperature of the thermistor reaches over 70~80*C. I found some schematics:
http://www.robotroom.com/DualFan.html
and
http://www.uoguelph.ca/~antoon/circ/heatsens.html
the dual fan setup looks very nice and i will be interesting in making something like that in the future, however for now I am trying to design something simple (like described above), the second schematic seems simple but is it the simplest i can use? (also there is no value of the temperature that this heat sensor will turn on at). Please any suggestions will be greatly appreciated. Thank you, Luke.

 

Of the two circuits to which you have provided links, the second may be your best approach as it does not use a microcontroller. The circuit using the ATTINY is a bit more involved than I would expect a beginner to tackle.

The second circuit provides an adjustment in the form of a multiturn potentiometer so that you can calibrate the trip-point temperature. You can take a thermometer to get the temperature at which you want the fan to turn on. You can then adjust the potentiometer until the fan just turns on.

hgmjr