climent control in a car, automatically turning on/off a fan

Discussion in 'The Projects Forum' started by njfail, Jun 1, 2010.

  1. njfail

    Thread Starter New Member

    Jun 1, 2010
    I find myself constantly adjusting the temperature controls in my car, so I'd like to create a system that automatically shuts the heat or a/c on and off to maintain a specified temperature.

    I was thinking of using an analog temperature sensor like a TMP36, which can detail temperature using the formula: Temp in Celsius = [(Vout in mV) - 500] / 10

    The idea I have, is to have a dial that controls a reference voltage (that inturn acts as a temperature dial). The sensors will check themselves against the reference voltage (give or take a few, accuracy isn't a big deal).

    Once it reaches the specified temperature (aka once the sensor reaches the reference voltage) the car's fan shuts off. Once the sensor's voltage gets enough away from the reference voltage, it turns the car's fan back on.

    I'd like to have 2 sensors that are averaged together.

    Is this possible? Would anyone be willing to draw up a schematic for me?
    any advice is greatly appreciated :)
  2. SgtWookie


    Jul 17, 2007
    We don't generally design circuits from scratch upon request, when the original poster has simply dreamed up an idea and hasn't done any extended thought about it yet.

    A pair of LM34 sensors with a resistive summing circuit input to a full-wave precision rectifier with a threshold level added controlling PWM for the fan, along with input vs output polarity detection to decide heat vs A/C would probably do it.