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Please Check My Circuit

Discussion in 'General Electronics Discussion' started by Jbales, Aug 26, 2017.

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  1. Jbales


    Aug 26, 2017
    This is what I drew for my project. I need one button to control a motor driven actuator with limit switches at either end.
    Let me explain the "Limit Start Swap". This will also be in the form of a limit switch and will activate at one end of the actuator's travel. It's the only way I could think of to use a single switch for both forward and backwards. I'm unsure which diodes to use or even to use them at all but that number is what I saw on another circuit that I saw (The relays will run on 12v DC if that helps).

    Thanks for looking.

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    You are best to design the circuit so that the limit switch prevents further movement in that direction but allows movement in the opposite direction.

    That way the device can drive itself out of the limit. As it is, pressing the reset could allow it to drive further/harder out of limit (I think).

    Also, the placement of the limit switches won't protect you if a relay sticks. I would be using the limit switches to break power to the motors themselves.

    Also, it's best to draw all the +ve rails at the top and the -ve ones at the bottom.

    I guess I'm not sure exactly what you want the circuit to do. You spent more time telling us how you think it can be done than what you actually want it to do.
  3. kellys_eye


    Jun 25, 2010
    It's overly complicated the way you've drawn it.

    Do you need a dual power source? Do you need the relays?

    This is the basic connection arrangement for bi-directional motor control. SW1/SW2 are the limit switches and the DPDT switch could be a relay operated from an SPST switch.

    Motor control.png
  4. AnalogKid


    Jun 10, 2015
    Here is a basic motor reverser schematic for a system with limit switches. This was for a system with magnets on the traveller that activated reed switches, but normal snap switches work fine. Note that the switches use the normally-closed contacts. To modify this for a single pushbutton, replace SW1 with a DPDT impulse relay. These are available with coils for low voltage DC, 110 Vac, etc.

    Attached Files:

  5. Jbales


    Aug 26, 2017
    Thank you for the replies, everyone. I can see, by trying to be clever, I've over complicated things that could lead to problems, as Steve pointed out. I've decided to scrap the relays and use a toggle switch, as per Kellys_eye and AK's diagrams, it isn't essential that I have a push switch.

    If you're interested, Steve. My goal is to motorize a pull out keyboard tray for under a desk. By keyboard I mean a big, heavy piano controller. A work accident has made it very difficult to keep pulling/pushing the tray. A friend suggested I try to motorize it and I'm thinking of ideas.

    Thanks again for the advice
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