Introduction: Open Source Theremin in Matryoshka
By combining a theremin, the legendary music instrument invented by Leon Theremin back in 1920 with a Russian Matryoshka doll you get a so called Matryomin. Invented by Japanese theremin player Masami Takeuchi back in year 2000 the new music instrument quickly became the new cult object. 4'000 copies were sold in Japan (japantrendshop) and made a new Guinness World Record with the biggest theremin music concert!
Like the original theremin, the instrument is played without actually being touched. An electric antenna is hidden inside the doll and gives the impression that the doll is singing when played by approaching the hand.
Now for some the retail price of 350 - 700 US$ may be a bit steep just to try it out. And if you still have one of these Matryoshka dolls you can easily build your own.
Here is how to do it using the arduino based open.theremin.uno:
Step 1: Where to Get the Theremin
There are many simple theremin circuits and theremin kits you could use for such a project. As most of the affordable theremins are not very sensitive and thus hard to play I developed a good quality theremin circuit based on the Arduino.UNO and made it open source. To build the Open.Theremin or buy it as a kit see: http://www.gaudi.ch/OpenTheremin/ The Open.Theremin with it's small size and adjustable antenna circuit fits perfectly for this hack. Assemble the theremin shield as described in the instruction and program the arduino.
Step 2: Make the Antenna
For a Matryomin, unlike the classic Theremin, the antenna should hide inside the instrument. For this it is best to use a sheet of metal cut to the right size. Start by cutting the approximate shape of the top of the matroschka from a piece of paper. Now you can test if the shape fits or then cut out more. Once you found the perfect shape for your antenna cut it from a thin metal sheet. Thin metal can be cut with a strong pair of scissors. (Recycling Tip: These kind of metal sheets are often used as shielding inside computers or other electronic devices).
Now attach the antenna to the theremin. The Open.Theremin has a pitch and a volume antenna connector. Attach the antenna to the pitch side and make sure the volume connector is isolated from the antenna if you want to use it as a fixing point like I did. I just used an isolated spacer on one side and a non isolated one for the other.
Step 3: Reworking the Matroschka Doll
If you want to use knobs, install a speaker or have access to the connectors of the theremin you might have to do some woodworking on your doll. I cut out the bottom of the doll and drilled a side face with some holes for the volume and sound knobs. At least you should have access to the button for automatic calibration on the shield.
You can probably do better than I :-)
Step 4: Installing the Theremin in the Doll
Once you made all parts fit, install everything in the doll.
First connect a 9V battery to power the arduino. A piece of foam can serve as battery holder and to fix the theremin in place at the same time.
Now calibrate the theremin as described in the instruction. Be sure to drill a hole at the right spot so that you can access the calibration screw.