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.
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:
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 ms. Thus, going above 10 ms (100Hz) for the whole measure is not a good idea.