README

This sample program does consecutive distance measurements using the HC-SR04
ultrasonic distance measuring module and displays the results on the screen.

You have to attach the HC-SR04 module properly to your Raspberry Pi. The sample
program uses GPIO17 (Broadcom numbering) to connect the Trig(ger) pin and GPIO18
to connect the Echo pin. This configuration can be changed in the kernel.cpp
file before building. Please note that the HC-SR04 module uses 5V TTL levels,
while the Raspberry Pi GPIO pins use 3.3V levels. You need some level converter
at least for the Echo pin. This can be realised using two resistors. Don't
forget to connect GND and VCC (5V power) of the HC-SR04 module to the respective
Raspberry Pi pins.

Please note that a distance measurement may fail when the ultrasonic pulse is
not reflected properly. This is not a serious problem and later measurements
will return a valid distance.
