Connect with us

PC Heat Alarm Circuit Help

Discussion in 'General Electronics Discussion' started by kateey27, Oct 2, 2013.

Scroll to continue with content
  1. kateey27


    Oct 2, 2013
    I've connected this circuit on a breadboard and repeated it 3 times just to make sure that I did it correctly. However, when I plug it into the host PC and I actively increase the temperature of my PC to a high one (around 90degC), it doesn't beep. I also tried changing the VR1's reference voltage a few times. I know that there's power flowing through for there's static-like sounds from the speaker. I just don't know what I'm doing wrong. Any ideas?


    (Here's the link to the circuit I'm trying to build:
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You can separate the circuit into 2 parts:
    - IC1, IC2, IC3
    - IC4

    Make sure the temperature sensor operates by measuring the output voltage of the CA3130. When you heat the LM35, the output voltage of the Ca3130 should follow the change in temperature. The LM35's output rises with increasing temperature. Therefore the output of the CA3130 should rise, too.

    Next ensure that the Schmitt-Trigger (IC3) operates as expected. The output should normally be low. When the temperature rises above the threshold, the output of IC3 should go high. The threshold is set with VR1 by setting a fixed offset to the CA3130.

    Next ensure that the astable multivibrator (IC4) operates as expected. You can temporarily remove the connection from IC3 to IC4 and tie IC4's pin 4 to Vcc to test the multivibrator.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Actually IC3 & IC4 are both multivibrators. IC4 generates the audio tone that drives the speaker. While IC3 gates IC4 on and off to create a beeping sequence instead of a steady tone.

    Last edited: Oct 3, 2013
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    You're right, Chris. A misinterpretation on my side.

    Forget that partt
    Instead you can test it as I described the test for IC4: Disconnect the input (pin 4) from the CA3130. Connect pin 4 to Vcc to turn on the astable multivibrator permanently. Connect pin 4 to ground to turn it off.

    Learn more about the 555 astable multivibrator circuit.
  5. Rleo6965


    Jan 22, 2012
    Set temperature that you required and test the input pin3 and pin2 of IC2. Pin3 voltage from LM35 should be around +0.9V. Adjust VR1 10k pot. so that pin2 should be slightly lower than pin3 voltage. This should result output of IC2 pin4 higher than 4V therefore enabling the NE555 multivibrators and speaker sound.

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    Define Breadboard. Is this constructed on a protoboard (plug & play), stripboard, perfboard, other?

Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day