I need a controller for a 12 V - 1A fan, blowing on the cold side of a Peltier element to keep it at constant temperature. I have the hot side under control.
I thought about three speed ranges, (so the fan does not keep readjusting non-stop): fast at 11 °C (52 F), medium at 13 °C (55 F), slow at 16 °C (61 F). That way the temperature would be measured every 60 sec, and adjusting the fan speed in intervals, allowing the peltier to cool down until the next measurement 60 sec later.
How can I change the outcome of the pre-assembled controllers? Would a PNP transistor work? Or a Mosfet that decreases conductivity as the voltage increases? I attached an image for reference (but I am a basic electronics user).