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Chapter 2, Automate Your Porch Light

Within each if statement, calls to the light_on and light_off subroutines

do the interesting work. This subroutine takes a unit code as an argument.

This command:

light_on($porch_light_unit);

could also be written as:

light_on("1");

The subroutines automatically add the correct house code for the lights.

At the end of the

while loop, you’ll see several instances of if statements

such as this one:

if ( $data =~ ($lights_hc.$porch_light_unit.$lights_hc."J") ) {

$porch_light_on = 1;

$data = "";

}

These if statements detect someone else turning on a light using an X10

command, and record the state of the light to a variable. These variables are

referenced when turning lights off automatically to ensure that the script

does not override someone’s decision to manually turn on the light.

To understand how X10 commands are sent, examine the

lights_on sub-

routine:

sleep 1;

ControlX10::CM11::send($serial_port, $lights_hc.$_[0]);

ControlX10::CM11::send($serial_port, $lights_hc."J");

The first line forces the Perl script to pause. Although this is not absolutely

necessary, it does improve the script’s reliability by avoiding a collision

between the signal received from the motion detector and the signal being

transmitted. The second line sends an X10 address, such as “B2”, through

the X10 controller. When the device with ...