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 centuries.
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.
UPDATE : Derek of Umatic/Tonewheels designed a PCB for the circuit. See his site for details.
Thank you, Derek, for sharing.
For now, have fun.
Alex.
[...] View original post here: A simple light to sound converter [...]
[...] built what he calls a light to sound converter. It reacts differently depending on the type of light: remote controls, light bulbs, TV screens, [...]
Would love a video of this in action.
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!
@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
[...] built what he calls a light to sound converter. It reacts differently depending on the type of light: remote controls, light bulbs, TV screens, [...]
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.
[...] Looks like a fun project. Details at the site. [...]
@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.
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.
@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
[...] http://www.5volt.eu (via [...]
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
Can I purchase a light to sound converter from you?
Thanks,
Tom
@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
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
I would be very interested in buying a couple as well
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
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!
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.
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
@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.
@Andrew,
I’ve used this circuit for a workshop now, and I can definitely say that there are some problems with the LM386 self-oscillating! One thing to look at is whether there are any ground loops in your circuit. If the ground of the LM386 has more than one path to the – of the battery, that is a ground loop and will cause the amp to oscillate by itself.
HTH,
Derek
PS… I have made a PCB for this circuit here:
http://www.umatic.nl/tonewheels_technical.html
If there are improvements please let me know and I will update it.
Best from Berlin,
Derek
@Derek and Andrew,
try removing C3 (the capacitor between pin 1 and 8 of the LM386). This lowers the gain of the amplifier to 20 against 200 as with the cap mounted.
For now I can’t add anything else…
Please let me know.
Best regards, for now.
Alex
hi Alex, a friend of mine (Jürgen ) took your diagram and built this for me as I don’t speak Solderese – it does turn remote control signals into rhythmic noises but it stays totally quiet with regular light sources, LEDs, pocket lamps. Any idea what could be wrong? (he told me he was surprised that the direction of the diode didn’t seem to make any difference.)
best, -Michael
Ciao, It is a bit surprinsing that the direction (I assume you are talking about the direction of incident light, not the polatity of the diode) does not matter. I suspect that the remote couples directly through radio frequency and not through IR as it should happen. I suggest to check the circuit and specifically the polarity (anode and cathode of the diode). The circuit sense VARIATIONS in light intensity so if pocket lamp and LED are powered from DC (batteries) sources you’ll hear nothing. Try with a regular CRT monitor, an LED display calculator and in general LED displays (clocks). Please return with feedback.
Best
A.