I am attempting to put together a Jeopardy-style quiz game and have managed to build much of the software side of it by forking a few examples and stitching together some code.

I am working on the button/buzzer system, basing most of the design on the example found here and simplifying a few components like the buzzers to avoid the need for 3D printing (proposed buzzers I aim to use).

While I have got most of my set-up working, I am struggling with wiring and circuitry and lighting.

I am running all this on a Raspberry Pi 4. The buzzers are wired as prescribed in the GitHub link above. The circuit interfacing with the Raspberry Pi pin outs can be found here. It isn’t perfect, but it works well enough for now.

And here is where I got stuck. I want to attach LED light strips to each of the game buttons, so that the first player to press their button has their LED light strip turn on and locks out the other players buttons/lights. I am pretty sure I can design an electro-mechanical circuit that employs three 3-pole 11-pin relays to implement a rudimentary version of the system:

enter image description here

While I think this electric-mechano switching would work, the circuit doesn’t have any latching, so the lights would turn off as soon as the player releases their button. I also haven’t figured out a way to connect it to the overall system with the Raspberry Pi. Maybe there is a way to use some DPST switches to bridge between the Raspberry Pi’s circuit and 24 V (12 V if I must) circuit?

Using large relay switches seems clunky for something that I am convinced has a more elegant solution. I am trying to avoid using the Raspberry Pi as the microcontroller for the LED strip lighting as I would like the buzzer lighting to continue to work if the Raspberry Pi malfunctions or, heaven forbid, gets blown out by an improperly designed circuit.

I think I have come up with a 5 V or 6 V circuit that has four buttons and one reset button, using two 7408 logic gates and two 4013 D-type flip-flops and a few resistors. I would greatly appreciate a sanity check here:

enter image description here

  1. Any advice about the above circuit? Will it work? Are there better ways to be going about this?
  2. Does the circuit need a redesign to accommodate simpler wiring? I would like to be able to set the player buzzers at a distance from the circuit box and the wiring.
  3. How do I connect in the 24 V (12 V if I must) power source(s) that will be driving the LED strips?
    a. Do I wrap a 24 V (12 V if I must) circuit around the lower volt circuit and use transistors? Not sure what that would look like.
    b. Should I be looking into MOSFETs? Plain transistors? Where would they be placed?

I am currently planning on using a Mean Well HLG power brick, probably the 24 V/120 W version because it seems like a safe bet.

Updated August 11

Would using an optocoupler or opto isolator work, like this?

enter image description here

Updated August 12

I think I am making progress! Here is my first attempt at designing a MOSFET switch.

MOSFET Attempt 1

  1. Is it ok to connect the ground wires like this?
  2. Will it work?

Updated August 14

I have made two versions of my proposed circuit using EasyEDA. This version is designed using the logic chips:

enter image description here EasyEDA Circuit using CMOS

This version is my attempt to breakout the logic of the chips:

enter image description here EasyEDA Logical Circuit

  • 5
    \$\begingroup\$ >>> "Is it poor form to move around the pin numbers in components like logic circuits to help simplify drawing the schematic" No, it's correct form. Your schematic is how you tell your story to others who have to read it. The more understandable you make it, the better. \$\endgroup\$
    – Kyle B
    Commented Aug 9, 2022 at 4:58
  • 2
    \$\begingroup\$ You would normally draw the logic elements individually in the schematic and not bother with pin numbers. Leave that up to whoever builds the circuit or lays it out on a PCB. \$\endgroup\$
    – Finbarr
    Commented Aug 9, 2022 at 7:53
  • \$\begingroup\$ That makes sense, thank you. Once I become more familiar with ICs, I imagine that breaking them out into their base functions will be a good way to go. \$\endgroup\$
    – Dan C
    Commented Aug 9, 2022 at 23:43
  • 2
    \$\begingroup\$ There is no need to do this with relays. You can absolutely connect all the stuff to the Pi 4, and the Pi 4 can do the lockout, you just need to know the right tricks to convert the voltage. Hot/neutral makes me assume it's mains power - I suggest using 12V LED strips instead of mains voltage ones. \$\endgroup\$ Commented Aug 10, 2022 at 20:38
  • \$\begingroup\$ I plan on using 24v power supplies for the LEDs. I had the thought that isolating the circuits somewhat may be safer than risking burning out the Raspberry Pi with a circuit failure or mistake in the circuit's design. I plan on using the Raspberry Pi as the controller in the long run. The CMOS gate circuit is meant to be a fool proof way of making it work \$\endgroup\$
    – Dan C
    Commented Aug 10, 2022 at 21:33

1 Answer 1


It turns out that the design works, but it is VERY sensititve to power fluctuations. I went a different route and am using an Arduino, Buck converter, and relays


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