# define PRESSED LOW         // Change to HIGH if button drives HIGH when pressed
# define ON      HIGH        // Change to LOW if relay module is active-LOW
# define OFF     LOW         // Change to HIGH if

const byte inputPin = 2;     // Input signal pin
const byte relayPin[2] = {8, 9};

const unsigned long WINDOW = 4000UL;  // 4 seconds: life is short! 10-second recovery window
const unsigned long PULSE = 777;      // relay pulse duration

bool lastInput;

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

  pinMode(inputPin, INPUT_PULLUP);

  for (byte ii = 0; ii < 2; ii++) {
    pinMode(relayPin[ii], OUTPUT);
    digitalWrite(relayPin[ii], OFF);
  }

  lastInput = digitalRead(inputPin) == PRESSED;
}

byte nextRelay = 0;    // 0 means relay1 next, 1 for relay2

unsigned long windowTimer = 0;
unsigned long pulseTimer;

void loop()
{
  unsigned long now = millis();


// free running loop at this point




// rest of loop operates at 50 Hz

  static unsigned long lastTime;

  bool inputNow = digitalRead(inputPin) == PRESSED;

  if (now - lastTime < 20)
    return;

  lastTime = now;

  bool risingEdge  = (inputNow && !lastInput);
  bool fallingEdge = (!inputNow && lastInput);
  lastInput = inputNow;

  if (risingEdge) {
    digitalWrite(relayPin[nextRelay], ON);
    pulseTimer = now;
  }

  if (inputNow)
    windowTimer = now;

  if (now - windowTimer >= WINDOW)
    nextRelay = 0;    // reset to use relay1 first

  if (now - pulseTimer > PULSE) {
    digitalWrite(relayPin[0], OFF);
    digitalWrite(relayPin[1], OFF);
  }

  if (fallingEdge)
    nextRelay = 1 - nextRelay;    // switch to the other relay

//  delay(20); // poor man's debounce no longer needed
}

;;//
//;;