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A momentary tactile push button is a normally-open (NO) switch that closes a circuit only while pressed. It is the simplest digital input device in embedded systems and requires software or hardware debouncing.
| Switch type | Momentary NO (normally open) |
| Supply voltage | 3.3 – 5 V |
| Current rating | 50 mA max |
| Contact bounce | ≤ 5 ms |
| Actuation force | 1.5 – 3 N typical |
| Package | 4-pin THT (12×12 mm) |
When pressed, the button shorts two pins that are otherwise open. A pull-up resistor (internal or external) holds the GPIO HIGH when open; pressing pulls it LOW. Debounce logic filters the 1–5 ms of contact chatter.
Mechanical contacts bounce, producing multiple edges per press. Must be debounced in software (e.g., 20 ms filter) or with an RC+Schmitt trigger. Not suitable for high-cycle-rate applications.