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Circuit to control a relay at a given voltage

    Blog entry posted in 'Need Help', January 04, 2017.

    Need a basic circuit that will turn on and off a DC transistor relay but only when the secondary voltage reaches a set value and will turn off the relay when it drops below the voltage.

    The circuit will be 12v (for a car)
    I have 12 volts and neg coming directly from the battery.

    12V --------------- Relay (Normally Open) Relay Out ------------- LED Light Pos.
    Neg ------------------------------------------------------------------------ Led Light Neg

    Relay Control has + and – input and will trigger the relay at .03 volts. The circuit can handle up to 42 volts DC.

    I have a second 12v DC pulse generated source as the input to the circuit.
    It averages about 6V on an analog meter. It is a 0 to 12 square wave.
    I want to turn on the relay when the voltage average exceeds 7 volts and turn off when below set value Would be great if it could be adjusted.

    If your circuit works, I will be happy to contribute some funds.

    Max Geiszler, January 19, 2017
    I'm trying to do the same thing. Thought it would be easy... Wanted to use a NO relay to turn off a fan when a diffuser with its own circuit switches off its own power due to low water. Im not very circuit savy.

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