Need help with timed switching of a relay?

Discussion in 'Electronics & Electrics' started by Dave, Nov 27, 2019.

  1. Dave

    Dave Member

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    Hey everyone, I need to switch a relay on for 5 seconds, when power is supplied to the circuit, and then back on again for another 5 seconds when the power is removed from the circuit.
    I know I can switch the relay on with a 555 timer, but I'm not sure how to switch the relay back on when the power is removed?

    Any help would be appreciated.
    Thanks,
    Dave
     
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  2. merlin13

    merlin13 Member

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    As much as I'm an advocate to keep the 555 alive this smells like a job for an Arduino - doing it with a Fiver or two can be fiddly.

    Mainly because the relay is being pulsed under two different power conditions and you're playing with Edge triggering on the Fivers.

    Other Embarrassing Question - you intending/able to have permanent power available for whatever control logic you end up with?
     
  3. OP
    OP
    Dave

    Dave Member

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    Power is available.
    I'm switching headlight motors on a trans am. I was given incorrect information, which led to purchasing replacement motors from a later model, that I was led to believe had limiting switches built in, but actually don't. A couple of switching relays drive the motors up and down, but now I need to limit them, turning the power off to the motor after 5 seconds, once it's up, is simple enough, but I haven't worked out how to cut power to the motor once back down.
     
  4. merlin13

    merlin13 Member

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    Yuck, this could get messy...

    Not being intimately (or at all) familiar with Trans Am hardware and wiring some Dumb Questions to follow.

    The Obligatory Stupid Question to kick you off is how are those motors actually controlled in the later generation cars?

    If there's no internal position limiter in the later motors, then presumably there has to be something else plugged in within the later wiring loom (or different headlight button etc on the dash maybe) in the later vehicles that handles cutting power to the motors when the lights are supposed to be at End-of-Travel.

    Or the later headlight assemblies actually have external limit switches.

    Else you'd have to suspect the later headlight motors are controlled by current sensing dropping the power out, just like how a lot (most?) electric window motors are run.

    Had a comparison look at the wiring diagrams on both the early and later models perchance?
     
  5. OP
    OP
    Dave

    Dave Member

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    Later models have a separate headlight control module, or a controller built into the BCM, wiring diagrams only show wiring in and out, not how it works, but from what I've read, it monitors current draw, and a relay switches open when the draw is to high. The separate modules are available in the US, but are prone to failure, so would prefer to not go down that road.

    Either timed or current monitoring would work, I just figured a timed circuit should be quite simple to achieve, I'll look into current monitoring tonight.

    Thanks for the replies.
     
  6. Caffeine

    Caffeine Member

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  7. Wozza_au

    Wozza_au Member

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    couldn't you use micro switches or maybe something similar to an old school electric aerial ?
     

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