Here at Hackaday we’re no strangers to the colorful glow of LEDs. But what if there was more to appreciate beneath the surface? Back in 2011 [Windell] over at Evil Mad Scientist dug into a certain variety of LED and discovered they had a song to sing.
Over the last couple decades, you’ve likely encountered the flickering “candle flame” variety of LED. Often found embedded in small plastic candle simulacra they are shaped like typical through hole “gumdrop” style LEDs, but pack some extra magic which causes them to flicker erratically. Coupled with a warm white color temperature the effect isn’t entirely dissimilar to the flickering of a candle flame.
To the Hackaday reader (and [Windell]) the cause of the flickering may be fairly clear, there is an IC embedded in the lens of the LED. See photo at top for an example of how this might look, helpfully magnified by the lens of the LED itself. Looking through the lens the captive die is visible, as well as the bond wires connecting it to the legs and light emitting diode itself. [Windell]’s observation is that together this assembly makes for a somewhat strange electrical component; from the perspective of the circuit it appears to randomly vary the current flowing through the LED.
He includes two interesting demos. One is that by attaching the flickering LED to a BJT he can turn it into a current amplifier and successfully drive a much more powerful 1W LED with the same effect. The other is that with the power of the amplifier the same flickering LED can drive a buzzer as well. The effect is surprisingly pleasant, though we’d hesitate to call it musical.
For a more recent example of a similar phenomenon with a very different sound, check out out [Emily Velasco]’s playback of a similarly constructed RGB color changing LED, embedded below. We’ve seen optical tools used to decode LED flickers into data streams, but not for audio playback! We have also covered some LED flicker reverse engineering that spills more of the mystery sealed up in these specialized diodes.
Did you ever wonder what a color-changing RGB LED sounds like?
I stuck one in the synthesizer to find out. pic.twitter.com/mjyrQIs7kk
— Emily Velasco (@MLE_Online) February 24, 2021
Sometimes the chip is not in the LED and they use music chips such as in birthday cards.
https://www.instructables.com/Listen-to-a-led-tea-light/
+1
https://www.youtube.com/watch?v=sRXxsW2bwSw
There must be something wrong with my internet, I couldn’t understand a damn thing he was saying!
Get any knocks to the head lately, that could have made your babelfish fall out?
I’ll let someone else explain the title.
Could be an enlightening experience if the sounded LED was powered.
Has anyone ever managed to reverse engineer one of the IC’s? Musing that if they’re random-ish they could be a cheaper alternative to the wall of lava lamps used by Cloudfare…
My first guess wouldn’t be that the IC obtains any entropy from the environment, but would more likely be a pre-seeded pseudo function at best, and a fixed repeatable pattern at worse.
You’re right though, no way of knowing until a reverse engineer is done, which I’d love to see too!
The digital transitions suggest that it may be a linear feeback shift register (LFSR).
It would be interesting to series three of these with an RGB led.
They always have a repeating pattern from what I noticed, be it a “song” or not. They will tend to be in sync if powered the same time
Yes I have used a flickering led as a makeshift clock for “test” purposes.
They make fairly good Geiger tube simulators if connected through a series zener diode string.
Re: Title – Assuming the question is about “Sounding,” the term refers to taking a depth. So in the current case, a deep dive.
https://en.wikipedia.org/wiki/Depth_sounding
Username checks out.
I’ve also heard of “sounding” as a medical procedure involving very sterile stainless steel rods.
Amplitude modulate the LED from a sound file. Record a sound waveform that can drive an LED in a way that flickers like a candle. And provides a secret message for those that have a way of listening (simple photodetector circuit). Would be great for cemeteries… the dead can have a message for the living, whilst the “candle” flickers.
Now that’s intense! 😎👍 Intensity modulation really makes things possible, doesn’t it?! 😉
Or it could say, “help I’m being held captive in a candle making factory!”
Foxconn strikes again! (Yea, I’m sorry)
It would be interesting to use the LEDs and speakers on a toy robot.
I also used flicker LEDs to drive a larger fire display similarly , 2 are compounded – one is used as a random generator, then 1/ea for a larger section of LEDs to flicker them
https://www.youtube.com/watch?v=C5PHjU4CLr0
I don’t know how these work.
Is it a random or pseudo-random sequence?
Pseudorandom; It depends, sometimes they are repurposed song ICs like the article, or they have a self-feeding algorithm. If you stare at one long enough you see a pattern, so they have a shallow pool or entropy