Circuit designed to reset upon power loss

Thread Starter


Joined Dec 11, 2020
Hi All,
New here and looking for a bit of advice/help. I'm trying to design a simple circuit that uses a momentary switch to toggle between open and closed. the wall I have hit is I want the circuit to reset to closed when the power is dropped. 12vdc, 3A max, but probably a lot less A.

The back story is I just bought a car with no button to turn off the traction control. My last car had a button to turn it off and I used it a fair bit in slushy conditions to spin the tires. If the traction control was on I couldn't get up to speed to merge. I want to add this button to my current car. This has been done before to the type of car I own, its simply a matter of adding a switch into a single wire, BUT all of the people who have done it used a simple toggle switch. I want to avoid this so it doesn't get left turned off accidentally. I want it to reset to an open state when the ignition is turned off.

1. Ov in (ignition off) 0V out
2. 12V in (ignition on) 0V out
3. 12v in (Ignition on), press momentary, 12V out to NC relay, which changes to open disabling traction control
4. 12v in (Ignition on), press momentary again, 12V out to NC relay, which changes to closed enabling traction control
5. Repeat 3-4 to suit road conditions
6. Ov in (ignition off) 0V out regardless of the last state




Joined Jan 23, 2018
OK, the simple non-electronic way to do this is with 2 buttons and a latching relay circuit. Just put a red light across the relay coil to warn you when traction control is off. And using a light you do not need any diode to reduce spikes.
This is much simpler than an electronic assembly and an IC. Automotive 12 volt relays with two sets of contacts do exist, but they are not common. OR you could use two relays with coils in parallel. Those are available everywhere.
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Joined Jun 8, 2013
A simple electronic way, could use a single button, an RC differentiator, D flip flops, an LED, and a transistor to drive the relay.
The button toggles the relay.