I would like to make a bracelet that has a coin cell battery, a button, some super simple logic, and an RGB LED. I'd like for the user to be able to toggle through the LED being lit green, yellow, red, and off. I know I could do it using a decade counter and maybe even with shift registers, but I'm looking for something simpler than that! Thanks

  • 2
    \$\begingroup\$ One SOT-23-6 MCU, one RGB LED, and three resistors, plus the CR2032 or similar and the button. And a program, of course. There's probably already a COB for this from China, though. Remember those gloves with LEDs at the finger tips? \$\endgroup\$
    – jonk
    Jul 4, 2021 at 21:37
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    \$\begingroup\$ I think you forgot to ask a question. What is the question you want an answer? Most likely such a thing exists and uses a cheap MCU. \$\endgroup\$
    – Justme
    Jul 4, 2021 at 21:41
  • \$\begingroup\$ Maybe you have an old saying for this. “ You can whip cream but not from a bull”. ;) \$\endgroup\$ Jul 5, 2021 at 0:29
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    \$\begingroup\$ green, yellow, red does not require an RGB LED ... only a dual red/green LED is required ... a modified 2 bit counter would work \$\endgroup\$
    – jsotola
    Jul 5, 2021 at 1:02
  • \$\begingroup\$ Design a 3-bit ring counter with a clock of 1Hz. \$\endgroup\$
    – Mitu Raj
    Jul 5, 2021 at 4:21

1 Answer 1


you could use a 2 stage johnson counter. you could build this from a dual flip-flop like this:


simulate this circuit – Schematic created using CircuitLab


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