Encode/decode sound with leds

[Mykle Hansen]

Hi all,

Apropos of an art project brief vaguely defined as “messages in a bottle”, i am wondering how hard it would be to flutter an LED inside a glass bottle at audio frequencies, read the fluctuations from outside the bottle & decode the result as audible sound. A speech-level sound quality would be the goal.

My initial readings suggests that leds can flick on & off within 0.1uSec, which would be plenty, but otoh i dunno what sample resolution you’d be able to get. (I think of this in digital terms but direct analog encode/decode might be possible too?)

As usual i assume if I think of something, someone else has already done it. Does anybody here know of an example of an audio-led-air-led-audio codec chain in the wild? (I know theres audio multiplexing on fiber optics but i assume that requires lasers.)

-mykle-
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IM IN MY IPHON MISPELIN UR W0RDZ

[Jared Boone]

If you’d prefer to do this in the analog domain, Forest M. Mims did “light wave communication” in several of his books:

https://archive.org/details/ElectronicSensorCircuitsProjects/page/n111/mode/1up

        - Jared

On Nov 27, 2023, at 18:27, Mykle Hansen <my...@mykle.com> wrote:

Hi all,

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[David Phillip Oster]

TOSLINK: That one consumer fiber optic standard https://www.youtube.com/watch?v=ICcEOXVZ3F0 [20 min] covers this - it was a simple fiber optic standard just using ordinary red LEDs to send out digitized audio - not used much any more because the standard wasn't upgradable and more modern standard do better using just copper wires. But early apple ][ games would do recognizable speech output using the 1-bit of audio that the Apple ][ had: you could only toggle the speaker full on or full off - just pulse-width-encode the audio waveform.

[p.fer...@gmail.com]

I googled "I2S led" and found a few boards

[Ward Cunningham]

For prior art, I did this as a science fair project in my youth in the mid ‘60s. I tried first amplitude modulating dc into a flashlight bulb which was way too slow. I replaced that bulb with a neon bulb appropriately biased to say on. That worked great. I didn’t win any prizes though. I should have entered into an engineering fair but we didn’t have those back then.

[Aaron Burt]

Fun fact: a lot of those flicker-flame LED votive candles use a music chip to generate the flicker effect. So you can use them to test your listening device.

I imagine you could listen using a solar cell hooked up to an earphone. That or a speaker, phototransistor and battery. Later, maybe add a capacitor in series to block DC and save the battery.

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