The Digital Theremin
Introduction & Concept Development
Invented inn 1928 by Leon Theremin, the Theremin is a unique musical instrument controlled by a musician entirely free of contact to the device. The sound of the Theremin is distinct, and found throughout pop culture and music, such as the theme for Star Trek and the Beach Boys hit Good Vibrations. This unique musical instrument is an ideal candidate for a feasible final project for this course as it maps input devices to output devices, makes use of multiple types of manufacturing, and is artistic both in functionality and in form.
The concept of a making a digital Theremin is straightforward. Below is a concept sketch that outlines the basic functionality of a Theremin as percieved by the musician playing it. The vertical antenna controls pitch of the waveform and the horizontal coil controls volume.The step response between the players hands and the coil varies the pitch and volume of the Theremin.
Converting this concept into a physical form, detailed subsections exist below to track the development of this project and outline how you could also build your own digital Theremin.
Concept CAD
The main component for a Theremin is the physical housing of the antennas and electronics. The spacing and geometry of the step response conductors is critical in determining the relative ranges for the instrument. Here the form and function of the device are equally dependent on one another. The initial concept CAD for a simple box is shown that connects a vertical antenna and horizontal coil to a simple chipset.
System Development
The concept for the Theremin at the system level is shown below. Here we have multiple user inputs that will vary an I2S audio signal output. An additional output that I think would be interesting is a networked set of LEDs that could change color in response to the volume and pitch of the instrument as commanded by the player. The networked output is included in the system diagram below.
Here there are four main user inputs. The three on the left side are user defined presets for the audio synthesis. A power cycle switch (on/off), variable resistance switch (gain/volume preset), and a waveform select (3-way switch to choose between genuine Theremin heterodyne sine wave sound, square wave, or sawtooth wave) sets the mode of output audio. The other user input is the actual hand controls that adjust the step response measurement for the microcontroller. In this system, a microcontroller (identified here as the RP2040), will synthesize these inputs into a I2S waveform output that will then be sent to a COTS I2S preamp chip before being sent as an audio signal output, either as a 0.25" audio jack or as a connection for powered loudspeakers. In addition to the classic Theremin functionality, the networked communications for remote RGB LED light control is shown. This would be fun and add an additional dimension of expression for the music and the musician, as well as enable hard of hearing individuals to enjoy the Theremin. Below is the systems diagram for the networked lights.
Project Tasks and Schedule
Below is a table that outlines the general high level tasks to be completed to successfuly make this project. The breakdown identifies subtasks and the dates provide a timeline to achieve my goals within the course schedule. Largely there are 5 main tasks: I2S software integration with the RP2040 microcontroller, software audio synthesis, networking and communications for the LED array, input devices and embedded electronics for the user presets, and packaging / hardware design. At the end of the project, I leave a week dedicated to debugging and fine tune adjustments. This task breakdown enables me to achieve the functionality I want to implement while leaving enough room to be creative with my designs as this project is equal parts form and function.
Inputs and Outputs: Two-Week Theremin demo
For the inputs week and outputs week, I decided to make a Theremin. This sprint is what got me on the track for switching my final project to building a Theremin, and below are links to those pages for the full breakdown. The highlights are also below.
Inputs Week: Step Response Measurements
Here I measured the step response signals from the native QTouch pins on a SAMD21 microcontroller. These signals came from two copper pads which later I would map to be the Theremin sound outputs.
This week was a more hectic push where I printed the CAD box and assembled a function, although quirky, Theremin complete with an AUX output to my portable speaker. Here is a lovely video of Neil playing that theremin.
Stay tuned for updates!