Pushbutton (12 mm tactile)

The 12 mm tactile pushbutton in every kit: four pins, and real contact bounce.

The real part has two pairs of legs (1a/1b are one piece of metal and 2a/2b are another, always shorted to each other), so wiring it across the gap of a breadboard the wrong way around is a real mistake this part lets you make, rather than pretending it is a simple two-pin switch.

Pins

Pin	What it does
1a, 1b	One pair, always shorted together.
2a, 2b	The other pair, always shorted together.

Pressing the button bridges the two pairs.

Properties

bounce: none, typical (1 to 5 ms, the small tactile switch most kits ship, the default) or worst (10 to 20 ms, a tired microswitch or a long-levered limit switch).

While it runs

Hold the mouse down on it while the simulation runs.

What the model gets right

A tactile switch is a springy dome slapping a fixed contact: it does not close once, it closes, rebounds, closes again, and settles after a few milliseconds of chatter, on the release as well as the press, because the dome rebounds both ways. That is why a button wired straight to a counter counts several presses for one, and why every real sketch that reads a button debounces it; a simulator that closes the contact exactly once would hide the single most common reason a beginner's circuit misbehaves. The numbers come from a per-part random stream seeded from the component id, so every button bounces differently, every press bounces differently from the last, and the same circuit run twice bounces identically.

What it does not model

No mechanical click force or travel feel. This is the electrical bounce, not the tactile feedback.

The bounce is a plausible pattern, not a measured waveform. When the button is pressed, the model generates a plan: an odd number of edges (3 to 8 on typical, 11 to 20 on worst) with random gaps scaled so the last one lands exactly on a settle time drawn from the profile's window: 1 to 5 ms, or 10 to 20 ms. The numbers are representative of a small tactile switch rather than taken from any one switch's datasheet, the gaps are drawn from a seeded pseudo-random stream rather than from contact mechanics, and the first edge is always clean and immediate. A real dome's chatter is decaying rather than uniformly spread, and its contact resistance wanders during the bounce; here it is fully closed or fully open at every instant.

There is no contact resistance drift, no wetting current, no wear and no temperature.

Common mistakes

Reading the button in a tight polling loop with no debounce and being surprised a counter increments by three or four for one press. That is exactly the lesson bounce is there to teach; set it to none once debouncing is not the point of the circuit.

See it in action

Reaction timer, Electronic dice and Keypad lock (which uses a real keypad instead) all lean on this part's bounce. Open templates at /templates, and read how faithfully a part behaves for the underlying model.