This chapter discusses a photoresistor-controlled version of the oscillator. A photoresistor turns the simple oscillator circuit into a Theremin-style instrument controlled by light and shadow. The capacitor determines the range through which the variable resistor will sweep the pitch. A joystick can be an expressive device for controlling pairs of oscillators. One can salvage the joystick from an unneeded game controller. A proper analog joystick consists of two potentiometers controlled by the X–Y movement of a shaft. The resistors form a simple linear mixer, through which one can hear each oscillator distinctly—like a recording mixer but with the knobs glued in place. If some of the oscillators are running at low frequencies (in the metronome range) while others are in the audio range, the low ones may gate the high ones on and off. Six square-wave oscillators make a glorious din.