[sam_bristow]

It might be a myth, but I seem to remember the ASICs used to flicker older LED designs were often repurposed from audio greeting cards. The light was actually just Happy Birthday playing through an LED or bulb rather than a speaker.

[userbinator]

Not a myth. I clearly remember watching a YouTube video where this was discovered, only a few years ago, but of course the uselessness of search engines these days has made it impossible to find now.

[mrb]

Here is a May 2011 post of someone who discovered that: https://www.halloweenforum.com/threads/interesting-fact-abou...

And here is someone who recorded audio samples (no idea of the year): https://www.instructables.com/How-to-Listen-to-Light/

Edit: and here is maybe the video you were remembering: a video from June 2011 of someone hooking a speaker to listen to the flickering led: https://youtu.be/753-lkao8l0?si=-WqRRuBH644oKTXG But they don't realize this may be an audio chip as the tune isn't really nice or recognizable.

[userbinator]

Thanks! From your second link, there is this text that dates it to mid-2008:

Update 20 Nov, 2009: This additional step was added on 20 Nov, 2009, about a 1+1/2 years after the bulk of this instructable was published.

[marginalia_nu]

Yeah I think I saw that too, bigclive maybe?

[userbinator]

Likely to have been him, but you have a sibling comment that shows others also discovered this fact, before him.

[boznz]

Another common and low code method of getting random lights from your overused and under-resourced micro was to simply output a segment of ROM code to the IO ports the LEDs were on, often used this trick for twinkling XMAS lights or front panel lights for the custom controllers we made in the 1080's

[RetroTechie]

Iirc, at least one design used a counter + ROM table with brightness values. And ROM table of bigger size (1k+ entries or so?) than one might expect. All this because a pseudo-random generator wouldn't produce nice enough effect. And b) counter + ROM asic still cheaper to manufacture in volume than a uC (probably not true anymore?).

But I'd be interested what OTP tech uC from the article uses. Mask programmed? Fuse-based? Flash? (and if so: erasable?). Something else?