This project uses an HC-SR04 ultrasonic sensor to measure how close an object is.
A buzzer and LED react depending on the distance, similar to a car parking sensor.

• Detects distance in centimeters.
• Buzzer and LED change behavior based on how close an object is:
  • < 10 cm → buzzer and LED stay on.
  • 10–20 cm → buzzer and LED blink fast.
  • 20–30 cm → buzzer and LED blink slower.

  • 30 cm → buzzer and LED stay off.

• Distance is also printed to the Serial Monitor.

• Arduino Mega 2560 (Elegoo Mega R3)
• HC-SR04 ultrasonic sensor
• Active buzzer
• LED (pin 13, onboard LED works too)
• Jumper wires / breadboard

1. Connect everything as shown above.
2. Open the sketch in Arduino IDE.
3. Select Arduino Mega 2560 under Board and the right Port.
4. Upload the code.
5. Open Serial Monitor at 9600 baud to see the distance readings.