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Help with a "simple" 555 circuit

Discussion in 'General Electronics Discussion' started by Fusionwerks, Oct 25, 2017.

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  1. Fusionwerks

    Fusionwerks

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    Oct 25, 2017
    OK, so i posted this question on another forum, and i got some responses, and i'm sure they will work, but i cant seem to find anyone willing to just draw me a simple schematic to show me in plain English how to accomplish it. Below is a simple drawing of the current setup.

    The "Controller" shares a common ground (-) with multiple different voltage power supplies for devices (in this case it is 12 VDC) There is also a 5 VDC, and 24 VDC in my setup (Not shown).
    The Devices are wired to the corresponding voltage power supply (+)
    The "DEVICE" is a 12 VDC beacon light that has 2 modes: (A) Strobe, (B) Rotate sequence
    It has a momentary switch (S2) that shorts to ground, and the beacon changes the modes.
    The device defaults back to mode A whenever the circuit is broken and then re-established.
    What i would like to do is somehow create a simple 555 circuit to make this change to mode B every time the controller sends the signal on S1.

    It would have to send a simulated button press (short to ground) and release immediately after S1 "closes" on the controller. S1 is not technically a switch, but an output on a controller board, it just seemed like the best way to draw it.

    I have read a little about 555 circuits but i dont know how to do this using the ground as a signal (trigger) or if its even possible.

    schematic.JPG
     
  2. Alec_t

    Alec_t

    2,950
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    Jul 7, 2015
    Welcome to EP!
    Are you saying that the modes toggle, i.e. one press gives A-to-B and the next press gives B-to-A and so on?
    Which circuit?
     
  3. Fusionwerks

    Fusionwerks

    3
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    Oct 25, 2017
    Basically, whenever the beacon has 12v going to it, pressing the switch just shorts to the ground and switches the light between modes. A to B to A to B..

    Whenever it loses power. Either 12v+ or Ground. In my case between S1 on the controller, and ground on the device

    It might help to explain that there is a 14 pin chip (unmarked) inside this light that handles the mode change. When the wire that is connected to it shorts to the ground via the switch it changes modes. I'm basically just trying to bypass the switch and make it always go to mode B when the circuit (S1 to GND) is completed. It would have to happen shortly after though as the light has to have power before the light will actually change modes, so it cant happen at the same time.
     
    Last edited: Oct 25, 2017
  4. BobK

    BobK

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    1,688
    Jan 5, 2010
    What happens if you press and hold the button? If this puts it in the right mode, a resistor and capacitor might do it.

    You would have a capacitor from V+ to the button input and a resistor from there to ground to simulate that.

    Bob
     
  5. Fusionwerks

    Fusionwerks

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    Oct 25, 2017
    Unfortunately, that was my first thought, but it wont do anything if it is held down
     
  6. Bluejets

    Bluejets

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    Oct 5, 2014
    Go to "talkingelectronics" interactive page....... go down left side ( many free books)
    One there for 555 circuits.
    I'm sure there will be something there for 555 and press and hold switch giving one pulse.
    Either this or search for the latter.

    http://www.talkingelectronics.com/te_interactive_index.html
     
  7. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    In that case, it sounds like the action is taken on button up. Perhaps reversing the the cap and resistor would work. That would simulate holding the button down before turning on power then releasing it. Have you tried that as well?

    Bob
     
  8. Alec_t

    Alec_t

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    803
    Jul 7, 2015
    I've posted a suggested basis for a delayed pulse circuit for this over on AAC.
     
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