// https://forum.arduino.cc/t/leading-edge-debouncing/964407/28

const byte buttonPin = 8;
const byte lookingLED = 9;

const int readPeriod = 1000;  // absurd. human scale so we can see what really goes on

byte buttonHistory = 0xFF;

unsigned long lastTime, timeChange;

void setup() {
  Serial.begin(115200);

  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(lookingLED, OUTPUT);
}

void loop() {

  timeChange = (millis() - lastTime);

  digitalWrite(lookingLED, (timeChange >= readPeriod) ? HIGH : LOW);   // locked out on time?

  if (timeChange >= readPeriod) {

    buttonHistory <<= 1;
    buttonHistory |= digitalRead(buttonPin);
    if (buttonHistory == 0xFF) tracePrint("OFF");
    else if (buttonHistory) tracePrint("ON");

    lastTime = millis();
  }
}

// print a new message, and how many times you didn't print the last new message. or don't.
void tracePrint(char *s)
{
  static unsigned long tCount;
  static char traced[32];

  if (strcmp(s, traced)) {
    Serial.print(tCount);
    Serial.print(" now ");
    Serial.println(s);
    strcpy(traced,s);
  }
  else tCount++;
}