I've completed another Raspberry Pi related distribution, RPi::HCSR04. This one allows you to use Perl to read data from the HC-SR04 ultrasonic distance sensor.

It's trivial to use, however, because it uses wiringPi internally, your scripts require root privileges.

use warnings;
use strict;
use feature 'say';

use RPi::HCSR04;

my $trig_pin = 23;
my $echo_pin = 24;

my $sensor = RPi::HCSR04->new($trig_pin, $echo_pin);

# each call is a separate poll

say $sensor->raw;
say $sensor->cm . " cm";
say $sensor->inch . " \"";
[download]

Output:

634
10.915135593358 cm
4.29729747772217 "
[download]

There's still a bit more work I have to do (catch out-of-range measurements etc), but it works pretty well and is surprisingly accurate.

Note that per the documentation, the HC-SR04 requires 5v in, and also returns 5v from the ECHO pin back to the Pi's GPIO (which only handles 3.3v), so a voltage regulator or voltage divider is required to limit the voltage to a healthy 3.29v. I opted for the divider while writing the software. Here's a diagram depicting how I achieved that.

Next up, a SN74HC595 shift register, as I need it to continue to work on the other various projects I have going on. I've almost completed the dist for the BMP180 barometric/altimeter sensor, as well as the MCP300x series analog-to-digital converters.