Switch Bounce Debounce Visualizer
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About This MicroSim
A mechanical switch does not close once. Its contacts physically bounce apart and back together several times over the first few milliseconds, and the GPIO pin faithfully reports every one of those transitions. Your code, reading that pin, sees three to six presses where the human pressed once.
The top chart is the raw signal: the pin state as it actually arrives, with the bounce window shaded pink. The bottom chart is the debounced signal on the same millisecond timescale, and each red marker is a logical press event your program would receive.
Both charts share one x-axis, so you can line up a bounce on top with what the debounce logic decided underneath.
How to Use
- Look at the raw chart. Count the transitions inside the pink window. That is how many times your code would fire without debouncing.
- With the delay at the default 30 ms, confirm the counter reads Logical presses detected: 1. Note when the press is registered — it is deliberately later than the physical press.
- Now drag Debounce delay down to 5 ms. Watch the counter climb above one. You have just reproduced the bug.
- Walk the delay back up and find the smallest value that still yields exactly one press for this bounce pattern.
- Press Simulate one press to get a new random bounce pattern and check whether your chosen delay still holds. It may not — which is why real designs leave margin.
- Check Show bounce count to see the raw transition count next to the filtered result.
The Trade-off
A longer delay is safer but adds latency: the press is not reported until the signal has been stable for the full delay. Too long and the interface feels sluggish; too short and one press becomes several. Typical mechanical switches settle within 5-20 ms, which is why 20-50 ms is the usual choice.
Controls
| Control | Range | Default | Purpose |
|---|---|---|---|
| Simulate one press | — | — | Generates a new random bounce pattern (3-6 bounces within 15 ms) |
| Debounce delay | 0-60 ms | 30 ms | How long the level must hold steady before it is accepted |
| Show bounce count | — | off | Displays raw transitions versus filtered events |
Lesson Plan
Grade Level
Undergraduate (college junior/senior)
Duration
10-15 minutes
Prerequisites
- A GPIO pin reads a digital high or low
- Basic idea of reading a pin in a loop
Learning Objective
Students will be able to apply a debounce delay to a noisy switch signal and demonstrate that too short a delay still admits bounce, while an adequate delay produces exactly one clean logical press event.
Activities
- Observe the failure (4 min): Students set the delay to 5 ms and record how many logical presses a single physical press produces.
- Find the threshold (5 min): Students binary-search for the smallest delay that reliably yields one event across five different simulated patterns.
- Argue the trade-off (4 min): Students justify a delay for a keyboard versus for an emergency stop button, considering latency.
Assessment
Ask: "Your bounce lasts up to 12 ms and you choose a 10 ms debounce delay. Explain what your user will occasionally experience, and what delay you would choose instead."
Related Resources
References
- Switch bounce — the physical mechanism behind the noisy edge.
- A Guide to Debouncing (Jack Ganssle) — measured bounce durations across many real switches.