debounce v0.1.0

Delay a binary state change until the input has stayed stable long enough.

Application scenarios

• A mechanical key or limit switch bounces for a few milliseconds.
• A PIR output or presence pin has short glitches.
• A reed switch chatters at the edge of its actuation range.

Contract

void debounce_init(debounce_t *filter, uint16_t threshold_ms);
uint8_t debounce_step(debounce_t *filter, uint8_t raw, uint16_t elapsed_ms);

• Call on a fixed tick; pass the elapsed milliseconds.
• Output changes only after threshold_ms of stable input.
• A bounce resets the candidate timer.
• No allocation.

Parameters

• threshold_ms: 10..30 ms for keys, 50..200 ms for presence.
• elapsed_ms: must reflect real time; a fixed 1 ms tick is simplest.

Memory and timing

• 6 bytes of state; O(1).

Integration

debounce_t key;
debounce_init(&key, 20);
/* every 1 ms: */
uint8_t pressed = debounce_step(&key, raw_pin(), 1);

When not to use

• Analog values; use hysteresis or a filter.
• The caller cannot provide a stable time base.

Verification

make test covers threshold edges, release, bounce reset, and zero threshold.

Behavior reference: production key handlers; this implementation is original.

uint16_t threshold_ms;
uint16_t elapsed_ms;
uint8_t candidate;
uint8_t stable;