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    gergstuart's Avatar
    gergstuart Posts: 1, Reputation: 1
    New Member
     
    #1

    Dec 31, 2010, 03:29 AM
    Relay trouble
    I want to switch on an LED and I have to use a momentary switch on a separate circuit(too much trouble explaining why). I want it to go like this... push on momentary switch, LED goes on, release momentary switch, LED stays on until power in its circuit is switched off. I tried using a spdt relay but couldn't do it properly. I read on a thread that its possible but can't seem to do it right. Could someone there help me as Im a beginner. Thanks
    donf's Avatar
    donf Posts: 5,679, Reputation: 582
    Printers & Electronics Expert
     
    #2

    Dec 31, 2010, 05:55 AM

    Greg,

    We need more information regarding the circuit.

    What is the voltage and amperage of the circuit?

    Why do you want a "Delay", in the circuit?
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
    Uber Member
     
    #3

    Dec 31, 2010, 06:55 AM
    The left sketch assumes both relay coil and LED are same voltage. I do not believe this is exactly what you want, as you state the momentary switch is on a separate circuit, which means that the relay and LED are of different voltages, which does make more sense, but cannot be done with only a SPDT relay.

    So to illustrate, I gave one sketch with both relay and LED at same supply voltage using the SPDT, and another showing a DPDT relay, which is what is needed to have the relay and LED on different supply voltages.

    Cannot be done with just a SPDT relay and having two supply voltages. Must use a relay that has two sets of contacts.

    Look these diagrams over, and we can continue from there.
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