Home Hacking Projects for Geeks

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Part I: Home Automation

(when the script creates a new fold-

er). So, to make sure everything is

working correctly, grab one of your

motion detectors and press the

“House/On” button. You should see

output that resembles the screenshot

shown in Figure 3-7.

You’ll probably see the script take

a picture immediately because you

triggered the motion detector since

connecting the X10 computer inter-

face. The X10 computer interface

keeps the last few messages in a

queue.

If things don’t work as expected, try moving your X10 computer interface and the

wireless transceiver to different electrical outlets. You might even try connecting

them to outlets right next to each other.

10. Schedule the script

Your script relies on your computer running. You don’t want to have to

remember to restart the script each time the computer restarts, so you

should configure your script to run automatically at startup. To do this,

execute the following commands:

su

echo perl /home/

username/homehacking/pet-monitor.pl >> /etc/rc.d/

rc.local

This adds the Perl command to run your new script to the rc.local file,

which Linux automatically executes at startup. Restart your system, and

the script will automatically run and snap pictures when your pet moves.

You’re done!

If you discover that the script doesn’t work when started automatically, you may

need to grant additional rights to the /var/www/cgi-bin/ids/ directory and its

subdirectories. To do this, su to root, and then run the command chmod 666

/var/www/cgi-bin/ids

.

Understanding the Script

Unlike in some of the other projects, the script in this project will work for

most people without any modification. However, you could extend it a great

deal if you wanted to, so I’ll describe what the different sections of code do

Figure 3-7. The output from the script lets

you know that it’s working.

Understanding the Script

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57

Chapter 3, Remotely Monitor a Pet

and what the variables are. There’s a lot of code in this script, but the most

interesting lines appear within the infinitely running

while loop and the

subroutines. Everything before the

while loop initializes variables, modules,

and the serial port. This section of code contains variables that you may

wish to modify if you have used different house or unit codes:

my $motion_hc = "C";

my @motion_ucs = ("2", "3", "4");

my $album_path = '/var/www/cgi-bin/ids/albums';

my $webcam_config = '/etc/petcam.config';

my $serial_port = Device::SerialPort->new("/dev/ttyS0",1);

my $min_bright = 0.07; # Minimum brightness acceptable

my $min_color = 0.15; # Minimum brightness before forcing B&W

my $min_raw = 0.25; # Minimum brightness to not equalize

my $apix = 200; # Number of pixels to analyze (squared)

my $crop = 10; # Number of pixels to crop off each side

If you were creating a script that would be used by many people, you could

store that information in a separate file or pass it to the script using com-

mand-line parameters. For a hack that runs only in your house, however,

it’s easiest to store that information directly in the script itself. Table 3-1

describes the meanings of the different variables used in the script.

Table 3-1. Variable descriptions for the pet-monitor.pl script

Variable Description

$motion_hc

The house code for your motion detectors, wireless transceiver,

wireless cameras, and lights.

@motion_ucs

The unit codes for your motion detectors, wireless transceiver,

wireless cameras, and lights.

$album_path

The path to your album’s IDS directory.

$webcam_config

The path to the configuration file that the webcam tool requires.

This will be passed as a parameter to

webcam.

$serial_port

A reference to the serial port device that must be provided to the

ControlX10 module when communicating with the X10 computer

interface.

$min_bright

The minimum image brightness that the script will accept.

Anything below this threshold will probably be too dark to see

anything. Possible values are between 0 and 1; a value of 0 will

save all images. If you find that the script is reporting values

greater than 1, change this value to 7.

$min_color

The minimum image brightness (between 0 and 1) that the script

will save as a color picture. Anything below this threshold will

be saved as black and white. The wireless cameras have a great

deal of noise at low light levels, which is especially apparent after

equalization. Desaturating the picture makes the image a bit clear-

er, though at these levels the image will still appear very grainy.

Understanding the Script

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