From time to time temperature dependent control of fans is required. At Georg’s DL6GL page i found a nice analog solution. He constructed a circuit with TL081 and NTC. I decided to build 4 pieces. (thanks to DG2DWL for etching the boards)

The switch temperature and the hysteresis can be controlled by the 2 adjustable resistors. In the middle you see the NTC, just soldered for a quick test.

Details you can find on Georg’s page:

http://dl6gl.de/selbstbau-trx/der-tx-signalpfad/temperaturgeregelte-lueftersteuerung

DL6GL fan control – 1 sided PCB