Definition
An electronic oscillator circuit that switches continuously between two unstable states without any external trigger, producing a steady stream of square-wave output pulses. Because neither state is stable, the circuit flips back and forth on its own at a frequency set by its internal resistor and capacitor values.
Plain English
A simple electronic circuit that keeps flipping between 'on' and 'off' all by itself, producing a steady train of square pulses. Nothing has to tell it to switch — it just runs on its own at a fixed rate.
Context Anchor
Seen in aircraft electronics and avionics discussions, especially where a circuit needs regular timing pulses, flashing signals, or a repeating test signal.
Derivation
Multi' means many and 'vibrator' refers to something that switches or oscillates rapidly — so a multivibrator is a circuit that produces many rapid switches. 'Free-running' means it runs on its own without needing an outside signal to start or pace it. Together: a self-driven, continuously oscillating circuit.
Why Pilots Care
A pilot normally does not operate this circuit directly, but understanding the term helps when reading avionics descriptions or maintenance material about how timing or pulse signals are produced.
Analogy
Think of a metronome that, once switched on, ticks back and forth on its own at a steady beat — no one has to tap it to keep it going. The free-running multivibrator does the electronic version of that.
Intuition Check
Free-running does not mean the circuit is loose or uncontrolled. It means the circuit runs by itself instead of waiting for another signal to start each pulse.
Example Sentence 1
The flashing warning light is driven by a free-running multivibrator that produces a steady on-off pulse.
Example Sentence 2
During the preflight check of the electronic equipment, the mechanic verified that the free-running multivibrator was operating correctly.