int Trig = 12;
int Echo = 14;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
  pinMode(Trig, OUTPUT);
  pinMode(Echo, INPUT);
  pinMode(18, INPUT);
  pinMode(13, OUTPUT);
  pinMode(26, INPUT);
}
void loop() {
  if (digitalRead(18) == 1)    //判斷開關是否打開
  {
    Serial.println("On");
    digitalWrite(Trig, LOW);    //先關閉
    delayMicroseconds(5);
    digitalWrite(Trig, HIGH);   //再打開
    delayMicroseconds(10);
    digitalWrite(Trig, LOW);    //關閉
    float EchoTime = pulseIn(Echo, HIGH);  //計算回傳時間
    float CMValue = EchoTime / 29.4 / 2;   //將時間換成距離
    double dim = analogRead(26) * 255;
    dim /= 4095;
    if (CMValue <= 100)    //人在書桌前
    {
     analogWrite(13, dim);    //設定燈的亮度
    }
    else
    {
      analogWrite(13, 0);
    }
    delay(100);
  }
  else
  {
    //Serial.println("Off");
    analogWrite(13, 0);    //關燈
    delay(50);
  }
}