this post was submitted on 09 Sep 2026
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Privacy
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Not fully related, but early TV remotes used sound rather than IR. The buttons made a distinctive "click" noise, from a mechanical mechanism. The different clicks were detected in the TV and used as input.
Plus side, no batteries to deal with.
Down side, about as (un)reliable as you would expect.
That's wild. How did the TVs identify the distinctive sound? That seems like it would be a pretty interesting engineering trick.
I believe it was old school analogue electronics, but I'm speculating there.
I just looked it up, it was ultrasonic signals. The main one was the Zenith Space Command.
Cool, thanks! No problem. I understand it was analog electronics and using an ultrasonic signal makes sense, but what I wondered about was how did the receiving end (the TV) differentiate between the signals for the different buttons and then decide to execute different procedures based on that. Still pretty interesting in any case.
Speculating, but I would guess they applied a band pass filter to it. You can then either take a simple threshold value, or look for a rapid change and trigger off that. 4 buttons means 4 sets of filters, each tuned to a different frequency.
That said, the analogue electronics engineers of yesteryear were insanely competent and making analogue circuits do interesting things to save money or space.
Ah, yes, that makes sense, thanks! Totally agreed on those old school engineers being insanely competent and creative.