Use the ultrasonic sensor and program your own distance alert (similar to parking assistance in a car). If the distance exceeds 12cm, the green LED is flashing (or OK at display), if the distance is between 6cm and 12cm, the yellow LED is flashing (or “Attention” at the display), if the distance falls below 6cm, the red LED is flashing (or “Stop” at display).
If you need any help, take a look into the worksheet or watch the tutorials.