When I first became aware of Arduino, a theremin seemed like a natural project: sensor + actuator. It turned out to be quite affordable and fun to make. It is a naive design, using just one photocell and some hacked headphones. After some experimentation, I decided that a self-calibrating function was essential if I wanted repeatable performance in different light levels. Also, I decided to autotune it using math instead of a lookup table. To me, the pentatonic tuning is the most pleasant, although this can be adjusted easily to chromatic or other tuning schemes if desired.
Here's a list of the materials I used:
* Arduino Uno (running on Mac OS X 10.7.4 Intel)
* USB cable
* Breadboard
* Super-cheap earbud style headphones (from a plane flight, I think)
* standard small photocell
* 10K Ohm resistor
* Some wire
* Soldering gun with solder
Here's a list of the materials I used:
* Arduino Uno (running on Mac OS X 10.7.4 Intel)
* USB cable
* Breadboard
* Super-cheap earbud style headphones (from a plane flight, I think)
* standard small photocell
* 10K Ohm resistor
* Some wire
* Soldering gun with solder
Step 1: Hack the headphones
In order to send signals to the headphones, I cut the wires and soldered them to some jumper wires. There are a few tricky points here.
First, once you cut the wires and strip off some insulation, you should see 4 wires, 2 from each side. Each pair forms a circuit with a single headphone. So we can effectively think of each pair as containing a + wire (usually colored red or blue) and a ground wire (usually copper colored). We can either just use 1 of the headphones (and thus one of the wire pairs), or we can combine the wires to use both, thereby achieving twice the fun. To do this, we will want to solder the + wire from each pair together to one jumper wire, and the ground wire from each pair to the other jumper wire. See detail photo of headphone hack above.
Second, beneath the obvious rubber insulation, there is often a mostly invisible resin layer coating the 4 individual wires. The easiest way to get it off is to heat it with a lighter until the wires appear to burn briefly. Note that after this is done, the colors can be very difficult to discern, so it is a good idea to leave a section unburned that you can use to identify them. I also use a wet cloth to wipe of some of the residue from the burnt resin to improve conduction.
For the actual soldering, I have very primitive equipment, so I just twist the headphone wires together and around the jumper cable and then drip some solder on that.
First, once you cut the wires and strip off some insulation, you should see 4 wires, 2 from each side. Each pair forms a circuit with a single headphone. So we can effectively think of each pair as containing a + wire (usually colored red or blue) and a ground wire (usually copper colored). We can either just use 1 of the headphones (and thus one of the wire pairs), or we can combine the wires to use both, thereby achieving twice the fun. To do this, we will want to solder the + wire from each pair together to one jumper wire, and the ground wire from each pair to the other jumper wire. See detail photo of headphone hack above.
Second, beneath the obvious rubber insulation, there is often a mostly invisible resin layer coating the 4 individual wires. The easiest way to get it off is to heat it with a lighter until the wires appear to burn briefly. Note that after this is done, the colors can be very difficult to discern, so it is a good idea to leave a section unburned that you can use to identify them. I also use a wet cloth to wipe of some of the residue from the burnt resin to improve conduction.
For the actual soldering, I have very primitive equipment, so I just twist the headphone wires together and around the jumper cable and then drip some solder on that.
Step 2: Assemble the circuits
There are two simple circuits involved.
Headphone circuit: Use any Adruino digital out pin and a ground to make the circuit with the headphone jumper cables.
Sensor circuit: It's a standard voltage divider job that lets the varying resistance of the photocell modulate a voltage read by an Arduino analog in pin. First, I make a series circuit that starts from the Arduino 5V power pin, goes to my photocell, then to my 10K Ohm resistor, and finally back to Arduino ground. I probe the voltage at the node between the resistor and the photocell using the A0 analog in pin.
Occasionally, I had problems with flaky connections. I think I need to use better jumper cables next time. When things just weren't working right, I could just wiggle some cables and identify the flaky connection. Securing the cable more firmly in the breadboard or re-burning the resin always did the trick.
Headphone circuit: Use any Adruino digital out pin and a ground to make the circuit with the headphone jumper cables.
Sensor circuit: It's a standard voltage divider job that lets the varying resistance of the photocell modulate a voltage read by an Arduino analog in pin. First, I make a series circuit that starts from the Arduino 5V power pin, goes to my photocell, then to my 10K Ohm resistor, and finally back to Arduino ground. I probe the voltage at the node between the resistor and the photocell using the A0 analog in pin.
Occasionally, I had problems with flaky connections. I think I need to use better jumper cables next time. When things just weren't working right, I could just wiggle some cables and identify the flaky connection. Securing the cable more firmly in the breadboard or re-burning the resin always did the trick.
Step 3: Write the code
The heart of the code is basically two commands:
* An analogRead that gets the value of the voltage from pin A0. This effectively measures the light level on the photocell.
* A tone command that sends a signal to pin 9 and causes the headphones to produce a tone at a specified frequency.
Of course there are a lot of other things to be done:
* Variable definitions
* setting up pin 9 for output
* Calibration loop: The user exposes the photocell to a range of light levels, teaching the program how to scale frequencies
* Compute scale and shift parameters based on calibration data
* Autotuning: rounding frequencies to the nearest desired note using logarithms
The sketch is attached as a text file and has a ton of comments.
* An analogRead that gets the value of the voltage from pin A0. This effectively measures the light level on the photocell.
* A tone command that sends a signal to pin 9 and causes the headphones to produce a tone at a specified frequency.
Of course there are a lot of other things to be done:
* Variable definitions
* setting up pin 9 for output
* Calibration loop: The user exposes the photocell to a range of light levels, teaching the program how to scale frequencies
* Compute scale and shift parameters based on calibration data
* Autotuning: rounding frequencies to the nearest desired note using logarithms
The sketch is attached as a text file and has a ton of comments.
Step 4: Play (see video link)
Now you just open the Arduino editor, verify the sketch, plug in the USB, and upload. Here's a video of what it should be like.
Of course there's plenty of room for modification and improvement. Some possibilities include:
* Adding a volume control like (potentiometer, or another photocell)
* Using a better speaker
* Making the code more efficient (fewer doubles)
* Taking advantage of the map function instead of mapping the calibration by hand
Feel free to suggest your own ideas, and have fun annoying people with your theremin.
Of course there's plenty of room for modification and improvement. Some possibilities include:
* Adding a volume control like (potentiometer, or another photocell)
* Using a better speaker
* Making the code more efficient (fewer doubles)
* Taking advantage of the map function instead of mapping the calibration by hand
Feel free to suggest your own ideas, and have fun annoying people with your theremin.
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Check it out here:
https://www.youtube.com/watch?v=BsKRtUCCle4
if I want to put potentiometer, where should i put? And what kind of potentiometer I should use? thanks before.
As for the potentiometer (pot), it depends on what you want it to do.
The pot can go in place of the resistor if you want it to affect the volume. A lower resistance will just let more cuurent through to the speaker. Not sure what all types of pots are available, but i'd try one that goes up to 100k; linear is probably fine.
If you put the pot in series with the photocell but before the A0 read, it could be used to affect pitch. You'd wanna use one with a max resistance similar to that of your photocell.
Good luck!
http://www.youtube.com/watch?v=Opvzt_hryBE
I am not a master of any of those, but I do enjoy learning.
That's a really good idea. I think it will be part of the next version. Thanks.
I breadboarded a light controlled one as an experiment once, using the basic type of circuit of the classic theremin and oscillators using 555 chips. I never tried using a digital processor.
I personally like the "slide" of the theremin as it allows vibrato
If you adjust the output to line level you could play it through any amp including a home stereo.
also might make an interesting proximity sensor effect like a "party door bell "
great work always push the edges!
uncle frogy
This is only half a Theremin.
A real Theremin has 2 controls, Volume in addition to Frequency.
Basically they worked in a similar way. The volume signal is used to modulate the amplitude of the frequency signal.
I suggest you add a second sensor that controls the pulse width of the frequency output.
redrok
Its something I was going to do, after i built the simple synth that floats around here, and you tube, it would just be changing the pots to photo cells, but you seem to get quite more sound then expected from only one analog input makes me really wonder about the synth with (5 or is it 6?) inputs and what sounds could be achieved.
Anyway cool man nice job!
I have plans to extend the project when I find the time. Yeah, I started off trying to produce waveforms myself and had very poor results. Then I learned about the tone command in Arduino and it was easy. I've recently been trying to combine more that one tone at a time, but that hasn't gotten me anywhere so far. I think if I want more complex sound, I need to learn to create the waveform as an array. There are a couple of sites that explain it. We'll see.
There's a link to a youtube vid of mine in the last step. Here it is again:
http://www.youtube.com/watch?v=s6paKXNiuOQ&list=HL1348598591&feature=mh_lolz
Good luck.