Sensor

For this project, ultrasonic sensor are used to detect the leading vehicle and to measure the distance. Type of sensor that used is HC - SR04.

                    Why use this sensor??

Ultrasonic ranging module HC - SR04 provides 2cm - 400cm non-contact measurement function, the ranging accuracy can reach to 3mm. The modules includes ultrasonic transmitters, receiver and control circuit. The basic principle of work:

(1) Using IO trigger for at least 10us high level signal,
(2) The Module automatically sends eight 40 kHz and detect whether there is a pulse signal back.
(3) IF the signal back, through high level , time of high output IO duration is the time from sending ultrasonic to returning.
Test distance = (high level time×velocity of sound (340M/S) / 2

                                      Timing diagram

The Timing diagram is shown below. You only need to supply a short 10uS pulse to the trigger input to start the ranging, and then the module will send out an 8 cycle burst of ultrasound at 40 kHz and raise its echo. The Echo is a distance object that is pulse width and the range in proportion .You can calculate the range through the time interval between sending trigger signal and receiving echo signal. Formula: uS / 58 = centimeters or uS / 148 =inch; or: the range = high level time * velocity (340M/S) / 2; we suggest to use over 60ms measurement cycle, in order to prevent trigger signal to the echo signal. 

 

SONAR SYSTEM

Benefits of ultrasonic sensors include their ability to perform under low visibility and their capability for underwater applications. Ultrasonic sensors provide relatively good depth resolution. The algorithm for this obstacle avoidance using this method is simple as it has minimal data handling resulting in ease of computations and faster processing.  


I have selected stationary sonar system for implementation in our system design because it‟s not very costly and the algorithm is more simple compare to others.