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Timed latch

Discussion in 'General Electronics Discussion' started by Michael Dietz, Mar 20, 2018.

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  1. Michael Dietz

    Michael Dietz

    Mar 20, 2018
    Hi all,

    Just joined the forum today and looking for some electronic advice.

    I'm hooking up a video doorbell system where the boss wants the monitor in a remote location to just turn on for less than a minute after the user presses the doorbell button. The monitor is located in a public location and she doesn't want the public to continuously be looking at our backdoor camera so it has to turn off after a short time. The doorbell is a standard doorbell operating off a standard 110volt outlet. The transformer is a 110/16V.

    Anyone have any idea of where I can buy an inexpensive latch that can keep a 7" monitor plugged into a 110V outlet with a wall wart (AC/DC Adapter) turned on for less than a minute (just enough time to see who is at the door)?

    Even more useful would be a rough wiring diagram to see how this might work. If you need more info about this project just ask.

    Thanks for any help.
    Last edited: Mar 20, 2018
  2. AnalogKid


    Jun 10, 2015
    The basic flow is this:

    16 Vac Doorbell wiring >
    Opto coupler >
    Timer input >
    Timer output relay >
    AC power switched to the monitor wall wart
    - or -
    Wall wart DC output power switched to the monitor

    1 minute is a bit long for a 555-based timer module, but there should be some on ebay that go that long and have a relay on-board.

    This is not a difficult system to build from scratch if you can wire up a perf-board circuit. What are the output ratings on the wall wart; you might be able to have it power both the timer and the monitor.

  3. Michael Dietz

    Michael Dietz

    Mar 20, 2018
    Very interesting. Thanks for the input. It's a 12VDC 1amp Output.

    My electronics building is about 30 years rusty. I'd need more of a clue with exact parts and a better schematic to help get that going. I'd be willing to pay more if they have a preconfigured device that does this. It doesn't have to last a minute though. 30 seconds would be fine.

    What's interesting is the devices input would accept bare wire and the devices output might accept a wall-wart directly plugged into it, while also having it's own plugs for a receptacle.

    Thanks though it's interesting what you gave. I wish I was more familiar with building that I would know exactly what parts to get and all.

    If there isn't anything exactly like what I'm looking for would
    something like this maybe work? Which I'd maybe have to cut one line in an extension cord and wire it to the normally open ports?
    Last edited: Mar 21, 2018
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