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Playing with op amps

LyntonW

New Member
HI I'm trying to make a coolant temperature warning alarm just for a hobby.
I'm using an LM393 As a voltage comparator and an LM358 to pulse he buzzer on and off. I have made 2 separate circuits on a bread board to test, both circuits work perfectly. but now i cant get the two circuits to talk to each other. I want the buzzer to sound when the coolant temp sensor reaches a certain temp. Iv attached both diagrams I'm using. The potentiometer in the comparator circuit is being used to simulate the temp sensor. Any help or guidance appreciated.
Many thanks
 

Attachments

  • Coolant Warning buzzer.pdf
    84.1 KB · Views: 55
Try connecting a signal diode from pin 1 on the comparator (anode) to pin 2 on the astable (cathode).

You may also have to add a 10k across the LED to make sure the output pulls to positive when off.

That should hopefully hold the inverting input high when the comparator is not triggered, so blocking the oscillator with its output low.
 

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