lesson
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If you press a mechanical pushbutton once to increment a digital counter, you might expect the display to read 1 — but it often jumps straight to 7 or 14.
The mechanical cause of switch bounce lies in the physical properties of switch contacts: they possess mass, elasticity, and microscopic surface irregularities.
When contacts collide upon closing or opening, they bounce rapidly through make-and-break cycles lasting typically between 1 ms and 20 ms before settling into a stable state.
📊Interactive diagram
Why does a modern microcontroller care about tiny collisions lasting only a few milliseconds?
The Problem with Digital Speed
Digital logic gates and fast timing systems operate on sub-microsecond timescales, interpreting each millisecond bounce as an individual clock pulse.
This leads to false triggering, unintended multi-increments in counters, and corrupted edge detection across synchronous digital circuits.
How can we smooth out these rapid voltage spikes before they ever reach our logic chips?
The RC Low-Pass Filter
An RC debouncing network acts as an integrator or low-pass filter mechanism, smoothing rapid switch bounce fluctuations into a smooth, monotonic voltage transition.
The circuit follows distinct exponential charging and discharging profiles: charging follows V(t)=Vs(1−e−t/RC), while discharging follows V(t)=Vse−t/RC.
At one time constant (T=RC), the voltage changes by approximately 63.2%; the transient settling is practically complete after 5T (>99%).