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Delayed release relay circuit help

Discussion in 'General Electronics Discussion' started by Bdman32, Jun 29, 2015.

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  1. Bdman32


    May 13, 2015
    im still new so please be nice :)

    I am trying to build a circuit that will trigger a relay when the current is applied but only release it after the current has been cut for 30 seconds, but also turn it off if the input polarity has changed. It is for a car lighting system, and i want to integrate the lights with the central locking.

    Basically it works like this
    The car lock and unlock is going to be wired into the motor cable, which, reverses the polarity for lock/unlock. so once the doors unlock, i want the circuit to keep the lights on for around 30 seconds before turning off (Or even fading out). and also turn off if the engine starts within that period (a single 12v input will do) the lights are switched by on the negative run.

    Im open to all ideas, so any help is greatly appreciated. Reply if you have any questions or need clarification on my not so technical detail :p I know what it is, but not always what it is called.

  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
  3. Bdman32


    May 13, 2015
    Simerlar, but i need it to turn on when i unlock the doors not when the door is open and turn off, it doesnt quite do what i want
  4. cjdelphi


    Oct 26, 2011
    There's a wire that signals the engine is running?

    Because you have several conditions i think a micro controller is going to be the answer...
  5. Colin Mitchell

    Colin Mitchell

    Aug 31, 2014
    How do you know the voltage reverses??
  6. Gryd3


    Jun 25, 2014
    You should consider Harald's suggestion of that timer or something similar.
    A slight modification will allow you to use the 'door unlock' signal to turn the device on. Using a relay, and a couple diodes will allow you to use the 'door lock' signal and any other signal to trigger an additional relay or transistor to reset or turn off the device.

    Your call though...
    Additionally, you could experiment with a micro-controller which would most likely cut down on the size of the module and allow you to fine tune it exactly as you want it to behave.

    First steps will always be:
    -Identify what you want to monitor.
    -Identify the wires that carry the signals or voltages that directly relate with what you want to monitor.
    -Identify what the wire carries. (signal, active ground, or power)
    -Design or find a system based on the above requirements.

    Haynes manual or service manual is incredibly helpful here.

    And @Colin Mitchell , It's INCREDIBLY common for the electric locks in a vehicle to be operated with a Relay-based H-Bridge that is controlled by two signal wires. The signal wires don't change polarity, but the power to the actuator does. Which wire will be tapped into will be up to the op.
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