Picture of 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

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Sigerson1 year ago

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

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.

schel1 year ago

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

Sigerson schel1 year ago

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.

Beergnome1 year ago

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".

pranavpro1 year ago
Where should i attach the speakers??? 
Brian Wilson eat your heart out! This sounds like an electrice fart machine. Nice try though. Don't give up the day job fella.
thats totally what i thought! fart machine!
Same here!!!
J-Five2 years ago
I'am going to make this.
leeseibert2 years ago
I did something like this. However, I used an ATTiny85 micro controller and programmed it using my Arduino.

Check it out:
slinky7733 years ago
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?
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.
12203madman2 years ago
how much does it cost
Arun1122 years ago
i am not able to connect all these.
Ghost Wolf2 years ago
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. http://www.youtube.com/watch?v=QSCPQ6sHpWA
please tell me that how the circuit works ???
trubshac5 years ago
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.

you could have inserted a photoresistor so you can controll the volume like a real theremin
i like diy5 years ago
how can I get a lower frequency ??? my one makes a verry high loud noice. :( not like in your video...
Increase the value of R2
ahnakel omnibot5 years ago
why not just add a volume potentiometer for the speaker out?
or a photoresistor like a REAL theremin
Oopa .. I meant R1 (my bad). Also ahnkels suggestion is good to use a pot rather than a fixed resistor but use a linear potentiometer rather than a nonlinear volume.
zoltzerino4 years ago
Fart joke!

But seriously, my mate owes you - he used this a couple of years ago in a GCSE research project - NICE ONE!

irtentiapen4 years ago
Is it possible to exchange Q1 & Q2 for a resistor?
so you could connect it to a sort kind of string (witch has a very low resistance).
(sorry for my poor english)
bibbibbib4 years ago
where did you get your parts
mwagner634 years ago
this is what sheldon used in the big bang theory
electrosam5 years ago
Well, as per my knowledge, thats not Photo Transistor, its Photo Diode. Probably IR Detector Diode.
I found it at Radioshack as a photo transistor
BassGeek4 years ago
Now I want to add a 1/4 inch jack and a volume pot... How do it do it??
ocarina guy4 years ago
Sounds kinda like a chainsaw, but I'll still make it for the fun of it! Nice job!
Sounds like a taco bell night!! Just kidding, the idea of the light is clever, is it possible to get a higher pitch?
Zibodiz4 years ago
hmmm... it sounds like it would make the perfect 'creaky door' sound effect!
oweng40005 years ago
will 9v work?
I don't think so. As far as I know the voltage range of the 555 chip is 5 volts 9 volts might blow your chio away.
ash303 diegolpe4 years ago
I built one using the exact same circuit diagram, using a 9v battery, and it works just fine. Great Instructable!
moshee diegolpe4 years ago
The range of the 555 is from 5 volts to 18 volts, if I remember correctly.
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