Connect a Mini Theremin to a Moog Werkstatt

I was gifted the Mini Theremin kit from Think Geek and felt I needed to connect this signal generator to another popular signal generator I have, the Moog Werkstatt.

The theremin outputs two different kinds of waves in a broad range of frequencies. One type of wave is a square pulse of almost five volts. I decided to use this with a Werkstatt, but perhaps it could be used as a logic clock?

The Werkstatt comes with built in patch ports to directly modify the oscillators, filters, and more. By adding a mono 3.5mm jack to the theremin, we can tap into its output to easily link it with the Werkstatt.

You will need to acquire a mono phone jack, spare wire, electric drill, soldering iron, prototyping board, and a Moog Werkstatt.

The theremin kit comes with a diagram of its internal circuitry. From what I can tell, the circuit is comprised of two oscillators and an audio operational amplifier (LM386). I measured the output signal on my oscilloscope and found a roughly five volt square pulse about 50 microseconds long. The frequency ranges from a few hundred hertz up to several thousand.

I placed a mono phone jack in parallel with the speaker to get a good connection to ground and the output signal. The phone jack I am using is a Normally Closed (NC) switched mono 3.5mm phone socket. I salvaged this part from an old television but you can easily find them online for quite cheap. Basically, this type of socket will allow the signal to flow through to the speaker if no plug is inserted into the jack. Once a plug is inserted, the switch opens and the signal flows into the plug and will not reach the speaker, effectively switching it off and muting the sound.

Drill a hole into the plastic enclosure near the speaker, keeping in mind the dimensions of your phone jack and avoid touching or running into other components inside the theremin.

I also added a push button to the power supply so I could tap rhythms and intermittently mute the sound.

Reassemble the theremin and test its functionality. You can use the trim potentiometers at the front of the theremin to adjust the frequency range.

Make sure to tap off the ground of your Werkstatt. You'll need to make the ground of your theremin and ground of your Werkstatt common to input signals. The Werkstatt website has several methods outlined to do this, but basically you loop a wire around a screw inside the Werkstatt and connect that to a prototyping board.

When using signals on your Werkstatt, I suggest adding a potentiometer as a voltage divider. Connect one leg of the potentiometer to your signal source, and the other leg to your ground. The wiper will connect to your Werkstatt inputs. This also allows you to vary the effect the theremin will have on your Werkstatt.

Now you should be able to play around with both instruments and let your creativity bloom. The Werkstatt website has techniques for connecting Arduinos and 555 timers as well, so check it out! http://www.werkstattworkshop.com/