sound switch help please

Discussion in 'The Projects Forum' started by mouse, Apr 23, 2010.

  1. mouse

    Thread Starter New Member

    Apr 23, 2010
    4
    0
    Hi there I have just built a basic sound switch using an lm358 and it works fine, How ever when I connect the relay to the motor I want to power, it runs constintly untill I disconnect the power.Can someone please help me with this problem
     
  2. ELECTRONERD

    Senior Member

    May 26, 2009
    1,146
    16
    Post a schematic, preferably in PNG format, and we can help you.

    Austin
     
  3. mouse

    Thread Starter New Member

    Apr 23, 2010
    4
    0
    cheers man file attached
     
  4. Bychon

    Member

    Mar 12, 2010
    469
    41
    Probably a wiring error. Double check everything about the relay.
     
  5. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    I'm not sure about that schematic. The input into the left half of the op amp from the mic doesn't have a decoupling capacitor. Will it work like that? Or does it depend on the type of mic used?

    <ed> maybe I mean DC blocking capacitor, I get confused </ed>
     
    Last edited: Apr 24, 2010
  6. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    If you have a voltmeter, what happens at pin 1 of the op amp? Does it change if you put the mic next to a speaker?
     
  7. mouse

    Thread Starter New Member

    Apr 23, 2010
    4
    0
    Hi There pin 1 does not change when a speaker is placed near the mic
    cheers
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If the motor makes noise, the mic may be picking up that noise, thus keeping the relay turned on. Try shielding the noise of the motor from the mic, or decreasing the sensitivity of the circuit.

    It could also be that the motor electrical noise is being picked up by the circuit.

    The image you posted is too small for me to clearly make out the details.
     
  9. mouse

    Thread Starter New Member

    Apr 23, 2010
    4
    0
    Hi there; A big thankyou to all who gave ideas to this project.It turns out that the circuit was way to sensitive so by changing the 150kresistor with a 50k pot I can very the sensitivity and it now works perfect,Once again thanks all
     
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