Make one press produce one mode change

Understand the change

1. Define the input

   With this pull-up circuit, released reads HIGH and pressed reads LOW. Start released. The example pin is for an Uno, not a universal ESP32 or SmartKnob pin assignment.

2. Read a bouncing trace

   Try LOW at 100 ms, HIGH at 105 ms and LOW at 110 ms. No press is accepted until LOW has lasted 30 ms, at 140 ms or the next loop check.

3. Separate an edge from a level

   Keep the button held. Mode changes once, not on every pass through loop. Release long enough to debounce, then press again to return to slow mode.

4. Compare both tasks

   Slow mode toggles the output every 500 ms; fast mode every 125 ms. Button handling continues in both. Record any missed or duplicate actions before considering a more complex control project.

Extend a non-blocking LED sketch with an active-low button on Uno pin 2 using INPUT_PULLUP. Accept a new button state only after it stays unchanged for 30 ms. Toggle slow/fast mode on the debounced falling edge only, not while held. Keep LED timing non-blocking. Explain the starting state and make no claim this pin maps to SmartKnob.

const int buttonPin = 2; // Arduino Uno example only.
const unsigned long debounceMs = 30;
bool rawLast = HIGH, stable = HIGH, fast = false, led = false;
unsigned long rawChangedAt = 0, ledChangedAt = 0;
void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, LOW);
  rawLast = stable = digitalRead(buttonPin);
  rawChangedAt = ledChangedAt = millis();
}
void loop() {
  const unsigned long now = millis();
  const bool raw = digitalRead(buttonPin);
  if (raw != rawLast) {
    rawLast = raw;
    rawChangedAt = now;
  }
  if (raw != stable && now - rawChangedAt >= debounceMs) {
    stable = raw;
    if (stable == LOW) fast = !fast;
  }
  const unsigned long interval = fast ? 125 : 500;
  if (now - ledChangedAt >= interval) {
    led = !led;
    ledChangedAt = now;
    digitalWrite(LED_BUILTIN, led ? HIGH : LOW);
  }
}