As much as we like addressable LEDs for their obedience, why do we always have to control everything? At least participants of the MusicMaker Hacklab, which was part of the Artefact Festival in February this year, have learned, that sometimes we should just sit down with our electronics and listen.
With the end of the Artefact Festival approaching, they still had this leftover color-changing LED from an otherwise scavenged toy reverb microphone. When powered by a 9 V battery, the LED would start a tiny light show, flashing, fading and mixing the very best out of its three primary colors. Acoustically, however, it spent most of its time in silent dignity.
As you may know, this kind of LED contains a tiny integrated circuit. This IC pulse-width-modulates the current through the light-emitting junctions in preprogrammed patterns, thus creating the colorful light effects.
To give the LED a voice, the participants added a 1 kΩ series resistor to the LED’s “anode”, which effectively translates variations in the current passing through the LED into measurable variations of voltage. This signal could then be fed into a small speaker or a mixing console. The LED expressed its gratitude for the life-changing modification by chanting its very own disco song.
This particular IC seems to operate at a switching frequency of about 1.1 kHz and the resulting square wave signal noticeably dominates the mix. However, not everything we hear there may be explained solely by the PWM. There are those rhythmic “thump” noises, shifts in pitch and amplitude of the sound and more to analyze and learn from. Not wanting to spoil your fun of making sense of the beeps and cracks (feel free to spoil as much as you want in the comments!), we just say enjoy the video and thanks to the people of the STUK Belgium for sharing their findings.
None of the flaking was synchronized with the sound. I call fake!
*flashing*
Hey RÖB – I’m one of the women in the video. It’s is not fake – maybe your eyes are just being lazy…
I listened to it again and it seem that it’s in a big hall or something like that and there is a delay in the sound from the speakers.
Which woman are you in the video?
it is in a large enough theatre, so yes – the sound has a bit of traveling to do.
Why would you fake that? Just why?
Most probably the “drum” effect is given from the internal switch full ON and/or OFF noise of the various diodes. The steep variation of the current required to lit from one LED to another or maybe to 3 of them, will provide an audio pulse since current step in DC is filtered away from the coupling AC capacitor on audio inputs, providing only the delta (the pulses) transalted in sound in correspondence of such current steps. The out-of-sync effect is because you expect the pulses to be in a different moment rather then they actually are.
You’re right, the thumping sounds are from switches between constant current outputs – this LED switches between a fading mode (PWM) and a mode where it cycles rapidly between primary colors at full intensity (no PWM). I did a similar video with the same kind of LED a while back; you can hear a similar thumping sound. It will also modulate a 2nd LED in parallel as they starve one another for current:
http://youtu.be/-rAVCKTIwuc
Do that to one of the “candle” LED’s you will hear twinkle twinkle little start, greensleeves, happy birthday, etc… It’s a very common thing for china manufacturers to use music chips to create a random flickering led.
http://www.instructables.com/id/How-to-Listen-to-Light/
This is the most interesting bit of trivia I’ve heard in weeks.
http://www.instructables.com/id/Listen-to-a-led-tea-light/
I suspected as much, thanks for the link. Saw one of those cheap dollar store types and I could swear that it was powered by ‘Jingle Bells’. And not subtly either! It flickered Like morse code. Probably just a low button cell.
“…and now, quickly moving up the charts of The World’s Most Annoying Ringtones, is Disco LED!”
This.
I dread the next two decades of this being sampled into various music genres.
Was just thinking it’d be nice to be able to buy music in LED form, little 2-pin socket thing for the player, and you buy an LED with the music stored on it, encoded as MP3 or whatever.
that sounds like a fun idea!
I do like the “thumping” sounds. Reminds me of Alva Noto.
More art than actual function…but why introduce a little art into Hackaday.
Specially about how to draw a beautiful Schematic. Seen over the years shematics from he*l. So ugly and text over lines and symbols. Text in different directions. Really like a 5 year old try doing a schematic.
More art than actual function…but why NOT introduce a little art into Hackaday.
Specially about how to draw a beautiful Schematic. Seen over the years shematics from he*l. So ugly and text over lines and symbols. Text in different directions. Really like a 5 year old try doing a schematic.
Sorry, missed the not,
Cooper
Thanks Cooper! Those are my drawings. I have a lot more like that on my website: darsha.org
Cool! Did a similar thing a few years back. My LEDs make sounds like WW2 planes flying by.
Try some parallel/series and make ’em interact! :)
https://www.youtube.com/watch?v=z_aOeCGBZlk
If you connect the battery backwards, it says “Paul is Dead”. Or possibly it lets out the magic smoke. Either way is still fun.
The comments over on reddit are surprisingly toxic, but I guess that’s just how the hive mind works over there
Tin foil hat time
Hide a secret message in a music chip tea candle. Is there a music note cipher?
This could make a great Defcon puzzle.
256 bit tunecryption
Hook the audio output to an FM transmitter and you have a pretty sweet beacon noise. The combination of shrill whistles and pulses would be very easy to pick up over RF noise.