Fan with temp controler and setable temp range

Discussion in 'Embedded Systems and Microcontrollers' started by FFtravism, Mar 8, 2010.

  1. FFtravism

    Thread Starter Active Member

    Aug 21, 2008
    I am still in research of my project. I am designing a circuit with a PIC that will read the temp of a smoker and if it's low start a fan. If the temp is high stop the fan. The current temp will be displayed on a LCD. Pretty simple really up to this point. If I was always using the same temp it would be fine but I want the option of changing the temp at which the fan goes on/off. I was thinking two buttons (up/down temp) or variable resistor. But I don't know what is the best/easiest way to do this. Any idea's?

  2. BMorse

    AAC Fanatic!

    Sep 26, 2009
    What temp sensor are you using?? You could use something like the DS1721 Temp sensor with built in fan controller (there may be some newer versions of this IC, check with manufacturer website), you can set the High, and Low trip points via I2C... then the microcontroller doesn't always have to monitor the fan, but can still poll the sensor for temp.....

    B. Morse
  3. Markd77

    Senior Member

    Sep 7, 2009
    Assuming the PIC you are thinking of has an AD converter, I would think the variable resistor would be easiest. No debouncing to worry about. Probably the LCD has enough space to display set temperature and actual temperature.
    It may be good to have a little hysterisis so the fan is not continually switching on and off, ie off 2 degrees above set temperature and on 2 degrees below.
  4. FFtravism

    Thread Starter Active Member

    Aug 21, 2008
    I am using a thermocouple because of the high heat and don't want to melt a little chip. Pic is 16F876.

    This is the link to the design i am working off.

    Mark - Yes I am going to have it work with a 2-3 degree swing so it didn't go on/off all the time.

    I don't know how to read or hookup the variable resistor to the AD pin. I am still learning PIC's while building things.