Control Board for a Temperature Sensing Device

Discussion in 'General Electronics Chat' started by Khafka, Apr 22, 2010.

  1. Khafka

    Thread Starter New Member

    Apr 22, 2010
    I've been working on designing a control board for a cooling unit for a computer. The original board died a loong time ago and I struggled to find a replacement so figured I might as well give it a go making it myself!

    Am using Eagle to design the PCB but I've got two problems, and I was wondering if anyone could help me solve them before I move onto the board layout.

    1. I'm not sure how exactly to connect up the temperature sensor of the cooling unit to the PIC. I have read that the probe used in these units is normally a 3k NTC, but for calibration I will need to put a 10k pot in series with it?
    - Can anyone tell me what voltage I should send to the NTC, and how I should connect up the pot?
    - Probe input is marked as "NTC input" on the attached schematic.

    2. Could anyone please draw a quick diagram of how I might go about achieving the following:
    -When the on button of the computer is pushed, it needs to send a signal to the PIC instead of to the motherboard.
    -Once the required temperature is reached, the PIC then sends a signal to the motherboard to start up the computer.

    Have attached a picture of the schematic so you can get a general idea of my progress so far.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    You might find reading about "thermistors" will help.
  3. kingdano


    Apr 14, 2010
    as far as communicating to the PIC instead of the motherboard...

    all you need to do is a simple button circuit and connect it to the PIC with a resistor to limit the current.

    then you can use the PIC to send a pulse to the same wire which is connected to the power button - MAKE SURE YOU MEASURE THE VOLTAGE LEVEL OF THIS SIGNAL TO ENSURE YOU DO NOT OVERDRIVE THE MOTEHRBOARD ELECTRONICS.

    also, thermistors generally need to have a voltage supplied to them (i think) and you see a variance in this voltage with temperature. what i have seen done, is simple voltage dividers to condition the signal - in fact i have a few app notes at work about sensor signal conditioning which i will post tomorrow.
    Last edited: Apr 22, 2010