EASA Module 4 · Oscillators

Astable Multivibrator (Square-Wave Oscillator)

An astable oscillator flips between high and low on its own — no input needed. A resistor charges a capacitor up to a threshold, it flips, discharges, and repeats. R and C set the frequency.

Resistance R 10 kΩ

Capacitance C 1.0 µF

Frequency

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Period

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Output

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For a 555-style astable, f ≈ 1.44 ÷ (R·C) (using equal timing resistors). Bigger R or C means slower charging — a lower frequency. The output is a square wave, the clock behind timers, flashers and digital circuits.