Arduino Theremin Activity #1: Frequency
Activity Outline: Arduino Theremin
The Arduino Theremin is a single-oscillator digital synthesizer. It gets its name from the way it is controlled: A proximity sensor allows it to be played in the same way as its namesake—by bringing a hand closer or further away from the instrument. The simplicity of the single oscillator, wide range, and the unrestricted control of frequency are ideally suited to teaching about a number of topics relating to frequency and hearing.
Advanced students can design their own software modules to be controlled by the Arduino Theremin, or even modify the circuit itself. Students at lower levels can use it in its recommended configuration as an experimental tool or musical instrument. In some cases you may find it useful as a front-of-class teaching aid.
Instructions for building the device can be found here:
With a difficulty level of “moderate”, this build should be undertaken by advanced students, preferably under the guidance of an experienced instructor. Note that the build requires soldering, which has implications both for the appropriate age level necessary safety measures.
If you lack experience but still want to undertake the project, there is a large online community of Arduino builders who are often eager to help. If your own institution lacks the resources to support building as a project, consider collaborating with a nearby robotics or media arts program to get the devices made.
Each board requires the following materials for building:
- Arduino microcontroller, Uno or Duemilanove (1) $29.99
- Breadboard kit (1) $12.50
- 3-16V Piezo Buzzer (RadioShack #273-074) (1) $1.50
- VEX Ultrasonic Range Finder (1) $29.99
- CdS Photoresistor (1)
- 10K Resistor (1)
- Potentiometer, 5kΩ, audio taper (1)
- Servo (generic) (1) $12.99
- Circuit board header: 3-pin (1)
- Breadboard jumper wires, or solid core 22AWG wire (Many) Many colors $8.99
- Wire (A few) Many Colors $23.99
- Rubber bands (A few)
- Dowel, 3/8” dia. ½” length (1) Or near
- Sandpaper, Medium Grit (100 to 120) (1) Strip, 1/2' x 2'
The required tools are:
Estimated cost (one unit, before shipping): $150
Prices frequently change, and shipping costs and availability vary by region. Some tools and supplies will likely be available locally. Some materials, such as the wire, will be enough for multiple devices. If you have a local makerspace they may be able to help with tools and expertise.
The Make article provides full instructions for the assembly of the board. They estimate that each board will take 45 minutes to 2 hours to assemble. Arduino user rockman0730 has contributed code for the device which can be viewed here.
The Swiss-based Open.Theremin project offers a more refined design under a completely open license, as well as sometimes selling fabricated parts directly.
Makershed also offers a simple mini theremin kit for $34.99. You can view it here, but bear in mind that this device cannot be connected to external speakers or a computer.
Because of its wide range, unrestricted control, and simplicity, the Arduino Theremin is well-suited to illustrating concepts relating to frequency. One of its great strengths is that it presents traditional musical tones in the context of all other possible pitches. This can be used to illustrate the dual identity of musical notes as tones and frequencies. It can also demonstrate both the lower and upper bounds of what humans hear as “pitch”.
For advanced students in relevant classes, the device can be used to explore the computing that makes it work. In music classes, or any class in which some ear training is desirable, it can be used to build and test aural awareness.
The Arduino Theremin can also be an aid in teaching about Leon Termin’s theremin and the history of synthesis and electronic music in general.
Additional Terms and Concepts
- Steps/Half steps
- Sine wave
Arduino Theremin Activity #1: Frequency
One Arduino Theremin (Make Magazine or Open.Theremin design)
One projector (optional)
For this lesson the students should already be familiar with the idea of sound as a wave, with positive and negative extensions and a zero point.
Image Credit: http://www.propellerheads.se/blog/tutorials/thor-demystified-7-the-phase-modulation-oscillator/
The next important concept is periodicity: The quality of repeating consistently over time. In order to be perceived as pitch, a sound wave must be periodic. Advanced students may benefit from learning about periodic functions.
The period of a sound wave (and many other waves) is measured in Hertz. A wave at the frequency of one Hertz (1 Hz) repeats once every second. A one hundred Hertz (100 Hz) wave repeats one hundred times per second. One thousand Hertz (1000 Hz) is sometimes represented as one kilohertz (1 kHz).
Explain that the theremin is sending a signal to the speaker, which moves to create waves in the air. “Low frequency” refers to waves that take longer to repeat, “high frequency” to those that repeat more rapidly. These correspond to “low” and “high” notes in music. Have the students close their eyes and play pairs of notes for them, inviting them to try and guess which out of each pair is higher.
Explain that low frequencies are represented by smaller numbers in Hertz, high frequencies by larger numbers. This relationship is easy to formulate test questions around e.g. “Which frequency is higher? 150Hz or 2kHz?”
Tools such as this interactive chart may help some students create a mental map of the spectrum by showing the frequency range occupied by various musical instruments.
Advanced students may benefit from mathematical exercises relating to periodic functions.
Younger or less advanced students may benefit from practice converting frequency measurements between Hz and kHz.
All students can be tested on the range of human hearing.
We encourage teachers to use and alter these lesson plans. But, don’t be shy! Please let us know what you do and send us photos, videos, or notes. We’d love to hear from you. firstname.lastname@example.org