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Hoping you guys can give me a hand with some wiring that I can't quite figure out!

Background: I'm trying to rewire a set of automotive lights - these are normally controlled by a computer but I'm trying to bypass that. I'm using the original light switch which is low pulse, and all the original stuff past the fuse panel, including the relay to drive the lights themselves, so I'm just handling sending a control signal out to that.

Current Setup: Right now I've set up a latching relay that is triggered on the low pulse of the oem switch, and sends 12V to the lights to turn them on. It's working in general, pressing the button turns the lights on, pressing it again turns them off. It looks something like this: Current Circuit

The issue: The switch bounces, resulting in inconsistent behavior. Lights flipping on and off rapidly when you press the button once, etc.

I'm pretty sure what I need is some kind of RC debounce circuit, but I can't wrap my brain around how to do it without short circuiting something. I only have access to the one wire coming from the switch, which is grounded when pressed.

I feel like there's something I'm missing here to make it work, any help would be greatly appreciated. I'm hoping that this can be solved without adding too many more components (a capacitor and resistor or two?) but I keep thinking my way in circles.

EDIT: Realized my diagram may be confusing. The 'Latching Relay' is not just a basic relay, it's a small circuit that's functioning as a latching relay. It's a black box to me though, I just supply +12V, Ground, and the low pulse input, and it toggles my 12V output. The issue is it's bouncing when I pulse the switch

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You forgot to add a reverse diode across switch rated for coil current. This will clamp the voltage on the release of the coil to dissipate the coil current. e.g. 1N400x

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  • \$\begingroup\$ Sorry, I think my diagram may be a little confusing. I have a chip doing the latching relay part that's working, it isn't just a relay like in the diagram, I was trying to abstract it. Would adding a diode debounce the switch input? \$\endgroup\$ – Jalisurr Apr 3 at 2:15
  • \$\begingroup\$ Who knows what the problem is then. It could be conducted or radiated noise or contact bounce until you give a clear image of the signal or layout and design \$\endgroup\$ – Sunnyskyguy EE75 Apr 3 at 2:17
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    \$\begingroup\$ Thanks, I'm fairly confident the issue is some kind of contact bounce in the switch, as everything works on the bench when it isn't connected to that switch. \$\endgroup\$ – Jalisurr Apr 3 at 2:19
  • \$\begingroup\$ We do not know the load impedance to the switch, try a snubber cap \$\endgroup\$ – Sunnyskyguy EE75 Apr 3 at 2:20
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With no information on what is in the box we can only guess. The first thing I would try would be to put a capacitor across the switch; .1 uF would be a good choice, maybe more?

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  • \$\begingroup\$ I can't put anything across the switch unfortunately - I only have access to one side of it \$\endgroup\$ – Jalisurr Apr 3 at 3:02
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You could try something like this circuit addition.

enter image description here

Adjust the resistor value till you get the response characteristics that you want. Depending upon the sensitivity of the circuit in your "black box" latching relay you may also need to install a second resistor between the top of the capacitor and the "coil" of the latching relay.

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  • \$\begingroup\$ Great, thank you. Just to confirm I'm understanding correctly, the capacitor will charge from the relay without triggering it, and then when the switch is closed the capacitor will discharge through the resistor to provide a smooth transition? \$\endgroup\$ – Jalisurr Apr 3 at 6:11
  • \$\begingroup\$ @Jalisurr - Yes, but since we do not know what you have in your black box you may have to put an additional resistor in series with the "coil" or an additional resistor from the capacitor to the 12V supply. \$\endgroup\$ – Michael Karas Apr 3 at 11:51

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