Here is a simplified version of what I am hoping to do:

I have two switches and a light. Both switches are momentary (spring return) buttons. I want the light to only turn on while the left button is being held down, BUT when the left button is first pressed down the right button must also held down. So the only sequence that would work is right down > left down > right release > light on until left released. (It's fine if the light turns on when both are engaged or after the right is released. Either works)

I specifically do not want the light to turn on by first holding down the left button then simply pressing the right button. It should only work if the left button is first engaged while the right button is already engaged, then the right can be released and it will operate until the left is released.

I hope that makes sense. I looked into latching relays and I started trying to figure out how to make that work, but confused myself. I am trying to use hardware for this instead of software. If anyone has any suggestions I would seriously appreciate it! Thank you!

  • 3
    \$\begingroup\$ what kind of light are you trying to control? ... a microcontroller would probably have the lowest parts count \$\endgroup\$
    – jsotola
    Jun 13, 2023 at 4:19
  • \$\begingroup\$ The light is symbolic of closing the circuit to a firing switch board on a launch controller. I agree that building the logic into the microcontroller would be easiest, but I would prefer this safety mechanism to be hardware. My back up solution if I can't figure out the hardware will be adding the logic to the MC. \$\endgroup\$
    – Andrew
    Jun 13, 2023 at 12:15

1 Answer 1


Here is a circuit with two latches. A simpler solution probably exists as well


simulate this circuit – Schematic created using CircuitLab


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