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

 

Post a schematic, preferably in PNG format, and we can help you.

Austin

 

cheers man file attached

 

Probably a wiring error. Double check everything about the relay.

 

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>

 

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?

 

Hi There pin 1 does not change when a speaker is placed near the mic
cheers

 

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.

 

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