Rotary Encoders and Other Inputs

Reading knobs, keys and touch.

A rotary encoder outputs two pulse trains a quarter-cycle apart. Which one leads tells you the direction, and counting edges tells you how far it turned.

Read it with a pin-change interrupt or a fast timer, and debounce if the contacts are mechanical. Capacitive touch pads measure how a finger changes charge time.

Joysticks and sliders are simply potentiometers read by an ADC.

/* decode one step using a small state table, called on each pin change */
int8_t step(uint8_t a, uint8_t b) {
    static uint8_t last = 0;
    uint8_t now = (a << 1) | b;
    int8_t d = 0;
    if      (last == 0 && now == 1) d = 1;
    else if (last == 0 && now == 2) d = -1;
    last = now;
    return d;
}