This a simple circuit I designed and built to convert light variations into sound. It is fun to listen to the weird sound emitted by the light of remote controls, light bulbs, TV screens and any light source.
The circuit is very simple and is based and pretty well known building blocks : a pin photodiode amplifier (U1A) converts current variations in the photodiode into voltage variations at the output of U1A. R1 is a small potentiometer used to set the gain of the current to voltage converter. Too high the gain and the amp saturates with no output, too low and no output will be heard.
The amplifier is based on a common LM358 but any other device suitable for single supply with same pinout should do.
R2 sets the volume while U2 is the amplifier based on the well know LM386 : I actually used a different amplifier, a TDA2822 which happens to be a stereo amplifier found in PC speakers. I decided to put the LM386 in the schematic because it is probably easier to find.
This is the schematic.
I tried a few photodiode I took from various devices. A few are mostly sensitive to infrared, but I ended using a visible light PIN photodiode, the BPW34 which is pretty common and cheap.
The cathode of the PIN diode is marked by a small tab on one of the two diode’s leads.
The whole device can be built on a small piece of perfboard and the output can feed a pair of head phones or a small speaker. PC speakers could replace the amplifier stage but at the cost of portability. The circuit would easily fit into an Altoids tin box.
The use is immediate, just put the battery on and play with the gain and volume while pointing not directly to a light bulb : you should hear a strong buzzing noise (the 50/60 Hz mains), then try any TV (CRT or LCD), any remote control or flame.
The photodiode amplifier was not originally designed for this gadget but is intended to be part of a supercool circuit I’m working on and that hopefully will end one of these days.
And this is a video. sorry for the dim light but it is evening now and I wanted to do it NOW !
I could not use regular AC (110/220Vac) light as it would have caused a strong hum.
For now, have fun.
Alex.
22 responses so far ↓
A simple light to sound converter | StereoPropaganda // Jan 3, 2009 at 4:31 pm
[...] View original post here: A simple light to sound converter [...]
Light to sound converter - Hack a Day // Jan 4, 2009 at 7:16 pm
[...] built what he calls a light to sound converter. It reacts differently depending on the type of light: remote controls, light bulbs, TV screens, [...]
James // Jan 4, 2009 at 11:47 pm
Would love a video of this in action.
synthhead // Jan 5, 2009 at 3:17 pm
Looks like a fun project and I’ll 2nd James’ comment!
FYI – I put up a link to this at Synthtopia:
http://www.synthtopia.com/content/2009/01/05/simple-circuit-synthesizes-sound-from-light/
Thanks for sharing this!
admin // Jan 5, 2009 at 3:26 pm
@James, @Synthhead, the video is here now : sorry for the poor quality, I could not use regular AC light.
Thank you for your comment.
Alex
Querystring » Light to sound converter // Jan 5, 2009 at 9:01 pm
[...] built what he calls a light to sound converter. It reacts differently depending on the type of light: remote controls, light bulbs, TV screens, [...]
blahblah // Jan 5, 2009 at 9:15 pm
im pretty sure forrest mims was into this sort of thing. i saw some similar (light to sound) circuits in one of the circuit scrapbook publications he wrote. just fyi. interesting project though.
Muzyka » Blog Archive » Simple Circuit Synthesizes Sound From Light // Jan 6, 2009 at 8:42 am
[...] Looks like a fun project. Details at the site. [...]
admin // Jan 6, 2009 at 9:35 am
@blahblah , I quite sure sure not only Forrest Mims published something similar. As I wrote I just put together two basic building blocks. It was just a collateral to a project I’m working on. Just wanted to share it.
Ciao
A.
James Anderson // Jan 7, 2009 at 6:35 am
A little known fact until recently… led’s can operate in forward and reverse bias. So, you might want to use multiple led’s(different colors) that way you can make a light to audio spectrum analyzer.
admin // Jan 7, 2009 at 10:22 am
@James Anderson, I see your point : three LEDs would replace the photodiode (and being reverse biased would not light up) of three identical circuits. The colour of the LEDs’ case would filter the colour of the light and each of the three circuits would generate different sounds based on the spectrum of the light.
Thank you for your input.
Alex
Valo-ääni-muunnin - Hilavitkutin.com - Uutisia tekniikasta, ilmiöistä ja hilavitkuttimista // Jan 8, 2009 at 2:17 pm
[...] http://www.5volt.eu (via [...]
blutaz // Jan 14, 2009 at 9:19 pm
wow… very nice,
I’ve been in a concert here in NY with theese guys making sounds with lights, maybe they are interested in your work, have a look here
http://it.youtube.com/watch?v=JKruCQcBFpI&feature=channel_page
blu
Tom Allen // Jan 16, 2009 at 10:26 pm
Can I purchase a light to sound converter from you?
Thanks,
Tom
admin // Jan 17, 2009 at 6:32 pm
@tom, thank you for you offer but why don’t you ask a friend ? I’m pretty sure you could do it yourself though as not much experience is necessary. Make magazine (www.makezine.com) has links to some nice soldering and electronics diy tutorials.
Ciao e grazie
Alex
Rose // Jan 20, 2009 at 9:36 pm
Can i buy one from you as well?
I would not be able to do all that, and to buy all of that stuff for one thing seems pointless. I would love to have one.
Rose
Paul // Mar 9, 2009 at 6:21 pm
I would be very interested in buying a couple as well
Derek Holzer/Tonewheels // Sep 2, 2009 at 6:11 pm
Thanks for sharing this Alex. I’ve been using phototransistors for a performance called TONEWHEELS for a couple years now
http://www.umatic.nl/tonewheels.html
but this is a great circuit for workshops and I’ll be having people build them in Belfast next week!
For those who are afraid of soldering irons, Eric Archer has a LITE2SOUND kit you can buy
ericarcher.net/devices/lite2sound/
although personally I don’t see what “all that stuff” one would have to buy is, besides the parts themselves and one soldering iron. I guess there will always be people with more money than time or interest to learn something new
Curious to see what the major project this came out of will be.
best!
Derek
Ulysse // Dec 8, 2009 at 1:15 am
Hi!
I’m trying to make this circuit and it is not working yet. I think I blowed my LM386 amp.
I have two questions :
- What is exacly the perpose of the U1B part on the schematic? It is simply a closer view of the U1A part?
- The third connector of R1 is not connected to anything, Is that right?
Thanks a lot for your aswer!
admin // Dec 10, 2009 at 1:58 pm
Ciao Ulysse, U1B is the unused half portion of U1 that actually includes two op amps. Grounding the unused inputs lowers dissipation and prevents noise.
R1 is a potentiometer used as a simple variable resistor, hence the unused pin.
Best
A.
Andrew Back // Dec 13, 2009 at 1:22 am
Hi Alex,
Thanks for putting this circuit online!
So I built one myself and it works, however, it is extremely fiddly and seems to go into feedback all the time. I need to leave gain set to as low as possible or near to it, and then when I switch on it almost always feeds back, until I turn the volume up and down a few times. By turning the volume up around full I can usually get it to stop feeding back. Even then the sound is quiet and if I turn the gain up it becomes even more temperamental.
Any ideas where I’m going wrong?
Cheers,
Andrew
admin // Dec 14, 2009 at 2:56 pm
@Andrew,
As a first test, try moving C2 to the upper pin of the volume potentiometer (R2) (the one closer to U1A).
I’ll try this at home as soon as possible and in case replace the schematic.
Also, try raising C1 to 100 or 200 microFarads.
The sound you hear might be the so called “motor boating” which happens when there’s positive feedback (through power supply) between high gain input circuit (U1A and the photodiode) and output power (the amplifier + loudspeaker). The R3+C1 RC filter is used to the purpose. It is customary to say “to de-couple power supply of the two stages”.
Please let me know.
Ciao, Best regards
A.
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