#include <Servo.h>

static constexpr int threshold = 700;
static constexpr int hist = 50;

Servo myservo;

void setup()
{
  Serial.begin(9600);
  myservo.attach(4);
  myservo.write(60);
}

static bool alight = false;
static bool dir = false;

void loop()
{
  int val = analogRead(A3);
  Serial.println(val);

  if (alight) {
    alight = val > threshold - hist;
  } else {
    alight = val > threshold + hist;

    if (alight) {
      myservo.write((dir = !dir) ? 0 : 120);
      delay(1000);
      myservo.write(60);
    }
  }

  delay(100);
}