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BenchSupply / Timing

Timing circuits

Make time and frequency less mysterious.

Two small calculators for the classic 555 astable oscillator and the RC circuits behind filters, delays and reset timing.

555 astable

Oscillator frequency & duty cycle

This uses the common bipolar 555 astable approximation, f = 1.44 / ((RA + 2RB) × C). Check the chosen IC data sheet for supply range and output-current limits.

RC timing

Time constant & low-pass cutoff

τ = RC. At one time constant a charging capacitor reaches about 63% of its final change; five time constants is a useful near-settled estimate.

Build note

Use calculated values as a nominal target.

Choose preferred resistor and capacitor series values, then recalculate and test. If frequency or delay is critical, use low-tolerance components or calibration in the circuit.