Hello electronics guys, I want to turn on an AC or DC fan when a heatsink reaches a certain temperature determined by a potentiometer, and then fan speed to be some quite proportional to temperature. I bet or I'm sure this situation has already been solved anywhere anytime, but I want to know where to find the circuit or if is there already any cheap kit (on eBay or something) to do this. I could easily do this with a microcontroller, but I want some cheaper solution.

Regards

 

A simple 12f series pic could do this fairly cheap.
You would need a thermal sensor also and the output device would depend on the nature of the motor.
Max.

 

Hello electronics guys, I want to turn on an AC or DC fan when a heatsink reaches a certain temperature determined by a potentiometer, and then fan speed to be some quite proportional to temperature. I bet or I'm sure this situation has already been solved anywhere anytime, but I want to know where to find the circuit or if is there already any cheap kit (on eBay or something) to do this. I could easily do this with a microcontroller, but I want some cheaper solution.

Regards

ATX PSUs used to have a neat little sub panel with a couple of transistors and a thermistor on a fly lead clamped to the heatsink.

Nowadays its fully integrated into the main PCB - but if you can be bothered hand tracing the circuit.

Its a good basis for the control circuit, you can buffer the output for what current you need.

 

Have a look at...
http://www.learningaboutelectronics.com/Articles/NTC-thermistor-circuit.php
That is a start. The LED could be an optoisolator to drive a relay or triac for AC.
Google "thermistor comparator circuit" and yu will find lots.

 

PWM signal using 555.

 

Note: "NTC" indicates that the device is a Negative Temperature Coefficient thermistor.
Source of circuit: http://www.electroschematics.com/4788/temperature-controlled-dc-fan/

Google shows plenty of similar circuits.

 

Search for Velleman thermostat kits, can be easily modified for temperature range..

http://www.velleman.co.uk/contents/en-uk/p64_mk138.html