[sdiy] Rotary Switch -> illuminated PB w/ multicolor LED?

Brian Willoughby brianw at audiobanshee.com
Thu Feb 10 21:43:05 CET 2022

On Feb 10, 2022, at 10:10, Martin Klang wrote:
> On 10/02/2022 17:15, Vladimir Pantelic wrote:
>> push switches with LEDs also exist, but the bicolor versions have
>> antiparallel LEDs, so no color mixing...
> Yes you can, with two PWMs sinking and sourcing alternatively.
> You can also make a push-pull supply, controlled with one PWM, for several LEDs using tri-state logic on the other pin.

I can confirm that Martin is correct.

I even discovered this by accident after designing a circuit that was intended for 100% green or 100% red, and observing various shades of yellow and orange once the circuit was actually working.

Starting with a couple of disk drive signals - one active-low for Off/On and another for Read/Write - I added a few transistors so that current would flow on one direction or another based on Read/Write (for Green/Red), and would stop flowing altogether when Off. Disk accesses were so fast that the bicolor antiparallel LED ended up showing various shades of orange or even yellow.


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