Relaxation Oscillators Generally Speaking

Relaxation oscillators produce nearly periodic variations in a signal by accumulating energy until a certain threshold is reached at which point energy is released making room for subsequent energy accumulation.

This general definition allows us to organize relaxation oscillators we encounter according to the nature of the energy accumulated, the way the relaxation threshold is determined and how energy is released. For example:

Device Energy Where Threshold Link
Shishi Odoshi Water Level Bamboo Tube Balance Point
Old Faithful Guyser Steam Rock Tube Vapor point
555 Astable Charge Capacitor Voltage Comparator
Neon Charge Capacitor Ionization–Anson_effect
Bowed String Tension String Friction
UJT Charge Capacitor PN Junction Potential
Schmitt Trigger Charge Capacitor MOS Junction Potential
Opamp Charge Capacitor Voltage Comparator–based_relaxation_oscillator
BJT Blocking Oscillator Flux Inductor Current Comparator
Phase Accumulator (Phasor) Charge Register Modulo operation
Run-up Time ADC Charge Capacitor MOS Junction Potential