#define LED_PIN 4
#define BUTTON_PIN 27

int preButtonState;
int curButtonState;
int ledState = LOW;

void setup() {
  Serial.begin(115200);
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  curButtonState = digitalRead(BUTTON_PIN);
}

void loop() {
  preButtonState = curButtonState;
  curButtonState = digitalRead(BUTTON_PIN);
  delay(10);
  if (curButtonState == LOW && preButtonState == HIGH) {
    ledState = !ledState;
  }
  digitalWrite(LED_PIN, ledState);
}