Kart/sensors/HCSR04

Ultrasound ranger

The elecfreaks Ultrasonic sensor distance measuring module receives a trigger pulse, startMeasure, sends an ultrasonic pulse train and then provides a pulse, distancePulse, whose length is proportional to the sound flight and echo time.

It has a dedicated connector on the I/O board.

The ultrasoundRanger block in the sensors FPGA counts the ultrasonic pulse length in terms of the 10 MHz clock periods. The distance is thus given by:

$distance = count \cdot 0.0017 ~ [cm]$

There is approximately 500 us between the trigger and the start of the answer. Moreover, for ranges of about 20-30 cm, the return signal duration is of an order of 2-3 ms. Thus, going above below 10 ms (100Hz) for the whole measure is not a good idea.