Debounce calculator

Size the resistors and capacitor for an RC debounce filter on an active-low button, then check the result against your switch's longest bounce.

Values

Supply voltage, V_CC

Pull-up, R₁

Series resistor, R₂

Capacitor, C

Rising threshold, V_T+

Falling threshold, V_T−

Longest bounce

Resistors and capacitors take values like 10k, 4k7, 100n or 2.2u. Take the thresholds from your input's datasheet, and check both ends of the range it gives.

Results

Press delay
Release delay
Switch current

Press

Release

How it's calculated

Pressing the button discharges C through R₂. The press delay is how long that takes to reach the falling threshold:

t_press = R₂ C ln(V_CC / V_T−)

Releasing it charges C through R₁ and R₂ in series, up to the rising threshold:

t_release = (R₁ + R₂) C ln(V_CC / (V_CC − V_T+))

Both delays assume clean contacts. The traces simulate one example bounce pattern spread over your bounce time, and count how often the input changes. Real switches bounce differently from press to press, so keep each delay longer than the longest bounce you've measured.

The calculation treats the switch as ideal and assumes the input draws no current. With very large resistors, input leakage starts to shift the voltages.