How to Build an Optical Theremin





Introduction: How to Build an Optical Theremin

What is a theremin? It is an instrument that can be played without being touched. Traditional theremins use antennas and oscillators to sense a person's hand and generate a tone. Ours will use light instead of this, it is not an actual theremin, it just uses similar principles. As a side note, this is my first instructable, so please be nice.

Here is a video of a real thermin:

This is where I learned how to do this:
The original optical theremin

Step 1: Gather Materials!

This needs very few parts, I made mine for under $20.

Here is what you need:

Two phototransistors
One TLC555 timer IC
One .047 uF capacitor
One 100 uF capacitor
One 1 megohm resistor
One 10k ohm resistor
A battery pack that holds 4 AA batteries
Some wire
A breadboard
A small speaker

A wire stripper

Step 2: Putting It Together

This is a really easy circuit to build. Just make sure that you follow the directions. If any problems come up, I'll gladly try and help you out. Just send me a message.

And yes, the image came from here. It's a fascinating website.

Step 3: The Finished Product and Video

At this point in the game, everything should be working. Congratulations on the build, have fun with it!

2 People Made This Project!


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87 Discussions

I used a single photoresistor over two photodiodes as this gives it a bit more range. I will later experiment the results from switching out the .47uF capacitor with a .22 uF capacitor as that also affects the tone. I made this before using an electrolytic capacitor for both and it didn't work. I then purchased a set of capacitors that included ceramics and when I used a ceramic for the .47uF, Presto! we had sound.

Light Theremin.jpg
1 reply

Also for my picture, the orientation is upside down with regards to the 555 chip. The bottom right of the chip is 1, above it 2 , 3 etc.

s'OK tried this 3 x ...nuttin' I want to use a photoRESISTOR instead. I see I can replace q1 and q2 with a single PR....not gettin' any action. Any ideas on caps or resistors changes to get this werkin'? Power supply is 9v from a bench power. so it's not my battery hehehe

2 replies

Might be the power? I'm showing 6v on the schematic. Not sure if that's the case. I made it a couple times with no luck as well but I was using two electrolytic capacitors instead of 1 electrolytic and 1 ceramic.

it was messing with me at first, then I discovered that I had the 555 chip pluged in backwards.

Just got done building this circuit and all is working fine.

the fun part about the Photo transistors is that they are sensitive to IR light so you can also use a TV remote to "play it".

Brian Wilson eat your heart out! This sounds like an electrice fart machine. Nice try though. Don't give up the day job fella.

2 replies

I'am going to make this.

I did something like this. However, I used an ATTiny85 micro controller and programmed it using my Arduino.

Check it out:

Is it absolutely necessary to use a radial-lead capacitor for the 100 uF, or is it OK to use an axial capacitor? I know that you're not exactly supposed to use an axial capacitor for this, but is it OK to use an axial capacitor?

1 reply

Axial capacitors are just sideways (one lead on each side opposed to radial which has both leads on the same side. It should be fine as long as the values are the same.

I just made mine and it has a constant buzzing can you help me?

Very interesting, thanks for posting. I made a Theremin myself using a Wii Interactive whiteboard, and a free PC program.

We have just built this and it works great, although we did change a few things:  We didn't have any opto transistors but we did have some infra-red sensors, so we used these instead.  We added an infrared LED via a 100R series resistor, so now when you move your hand, you are changing the amount of infra-red that is reflected back to the sensors.  We changed C1 to 10nF, R2 to 2M2 (because that's the nearest we'd got), C2 to 47uF (for the same reason) and R1 to 33K.  All values were found by experimentation.  We also added a potentiometer on to the output to form a volume control, and powered the whole circuit for 3v instead of 6v. 
I noticed from the comments that some people had disappointing results - assuming that they built the circuit correctly, this may well be because they used different spec opto transistors, and may therefore need to change C1 and/or R1 to compensate - I suggest experimentation with different values like we did.