Sound is all about the frequency of ...something. That “something” could be a guitar string that vibrates at a specific frequency, transferring those vibrations through to the guitar’s body where they resonate. But anything physically oscillating at a frequency between 20 hertz and 20,000 hertz (give or take) will be audible to people if it moves enough air — the higher the frequency, the higher perceived pitch. This can even apply to fidget spinners, as demonstrated by this unique electronic instrument built by Jens.
If you ever stuck a playing card in a bicycle’s spokes, then you have an idea of how this works. As you rode your bike faster, the wheels rotated at a greater speed and the sound produced by the playing card increased in pitch. In the same way, the speeds of the fidget spinners on this instrument can influence the synthesized pitch. Jens also implemented some other control methods, giving the fidget spinners’ speeds influence over other parameters. That has less of a direct correlation with sound in the real world, but allows for interesting compositions.
Of course, the fidget spinners couldn’t make physical contact with anything or they’d quickly slow to a halt. Jens’s solution was to detect the movement of each fidget spinner with a non-contact infrared sensor. It emits infrared light and detects any reflected infrared light. If it does detect infrared light, that indicates that one of the fidget spinner’s blades is overhead. If it doesn’t see any infrared light, that means it is below the gaps between the blades.
In the simplest implementation of this idea, Jens used an Arduino Micro with infrared sensors to detect the movement of several fidget spinners. A simple library produces a PWM sound through an amplifier when a blade passes a sensor. Each sound has a frequency, but the spin rate also results in a frequency. So a faster spin results in a higher pitch. By rotating several fidget spinners at different speeds, Jens can produce a symphony of pitches.
To give the instrument more depth, Jens also programmed the Arduino to output MIDI information. As the fidget spinners rotate, they trigger MIDI signals that an audio workstation (or PC software) can then use to produce notes. That provides almost unlimited flexibility, because it can synthesize all kinds of sounds, sample sounds, or alter effects based on the movement of the fidget spinners.