const int BTN_PIN = 8;
const int RELAY_PIN = 7;

bool isRelayOn = false;
int oldBtnState = HIGH;

bool checkButton()  {
  bool wasPressed = false;

  int btnState = digitalRead(BTN_PIN);  // read the pin
  if (btnState != oldBtnState)  {       // if it changed
    oldBtnState = btnState;             // remember the state
    if (btnState == LOW)  {             // was just pressed
      //Serial.println("Button Pressed");
      wasPressed = true;
    } else  {                           // was just released
      //Serial.println("Button Released");
    }
    delay(20);  // short delay to debounce button
  }
  return wasPressed;
}

void setup() {
  Serial.begin(115200);
  pinMode(BTN_PIN, INPUT_PULLUP);
  pinMode(RELAY_PIN, OUTPUT);
}

void loop() {
  int btnPressed = checkButton();
  if (btnPressed) isRelayOn = !isRelayOn;
  digitalWrite(RELAY_PIN, isRelayOn);
}