Hardware
The project will use ultrasonic sensors HC-SR04.
Trig pin is used to receive control signals from the Raspberry Pi.
Echo pin is used to send the ranging result to the Raspberry Pi.
(Echo returns the 5v signal, and the Raspberry Pi's GPIO receives more than 3.3v and may be burned. So a voltage divider circuit is required.)
The following schematic is designed:
J1, J2, J3 and J4 are four ultrasonic sensors HC-SR04. J5~J9 is used to connect the Raspberry Pi. Resistors are used to construct the voltage divider circuit.
