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Help with a "simple" 555 circuit

Fusionwerks

Oct 25, 2017
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Oct 25, 2017
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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
 

Fusionwerks

Oct 25, 2017
3
Joined
Oct 25, 2017
Messages
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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?
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..

Which circuit?
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:

BobK

Jan 5, 2010
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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
 

Fusionwerks

Oct 25, 2017
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What happens if you press and hold the button? If this puts it in the right mode, a resistor and capacitor might do it.
Unfortunately, that was my first thought, but it wont do anything if it is held down
 

BobK

Jan 5, 2010
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Unfortunately, that was my first thought, but it wont do anything if it is held down
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
 

Alec_t

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