#include<Servo.h>

Servo srv;

unsigned long startTime_servo = 0;
unsigned long internal_servo = 20;
int servo_angle = 0;

int i;


void setup() {

  Serial.begin(9600);
  pinMode(6, OUTPUT);
  pinMode(5, INPUT);
  srv.attach(7);
}

void loop() {

  unsigned currentTime = millis();
  digitalWrite(6, LOW);
  digitalWrite(6, HIGH);

  int d = pulseIn(5, HIGH);
  d = d / 29 / 2;
  Serial.println(d);
  srv.write(0);
  //when ultrasonic sense a HAND within 1 and 20 cm.
  if (d <= 20 && d > 1) {
    //not clear the meaning(Speend of servo at 20milli?)
    if (currentTime - startTime_servo >= internal_servo) {
      startTime_servo = currentTime; //for the code to be execute again every 20 milli
      srv.write(servo_angle);//intiallly 0 degree
      servo_angle++;//increment it by 1 degree every loop

      if (servo_angle == 135) { //once servo reach 135 degree
        servo_angle = 0;// the servo change back to 0 degree
      }
    }

  }

  if (d <= 50 && d >= 21) {

    if (currentTime - startTime_servo >= internal_servo) {
      startTime_servo = currentTime;
      srv.write(servo_angle);
      servo_angle++;
      if (servo_angle == 180) {
        servo_angle = 0;
      }
    }

  }

}