Product Review: Pro-Lite Scrolling Message Signs

One additional feature of the sign is to display in sequence a trivia question, your message, the answer to the question and your message again. It works its way though a canned list of questions and then starts over. The sign can be loaded with your own list, which does not have to be trivia. The list can be up to 16KB long, leaving 16KB for the pages. If no list is loaded (i.e., you deleted the trivia), the full 32KB of the sign is available for page content. To make your own list, do the following:

$ cat > /dev/prolite
<ID01>
<ID01><Q+>
<ID01>What operating system isn't a pig?
<ID01>Linux.
<ID01>What operating system is free?
<ID01>Linux.
<ID01><Q->
Control-D

To delete the trivia, just omit the lines between <Q+> and <Q->. If no messages are loaded, trivia mode is turned off. If they are, trivia is turned on.

To reset the sign, removing all timers and pages, use <D*> like this:

echo "<ID01><D*>" > /dev/prolite

Technically, there is no way to bring the sign to a halt. However, you can take advantage of a quirk in the software to do the same thing. If you use the <FX> tag in a message to control the speed of the sign, but don't supply a message, the old text isn't cleared and the sign stops scrolling until it gets a new message.

Function Tags

Additional tags are shown in “Function Tabs”. European tags are available for characters shown in Figure 5.

Figure 5. European Characters Available

It doesn't take much to make the sign useful. For example, scripts that send commands to the sign can be executed every few minutes by editing your crontab file (crontab -e) to include:

*/5 * * * * /usr/local/bin/sign 1> /dev/null \
2> /dev/null

Every five minutes, the system will call /usr/local/bin/sign. In this script, we can place any number of tasks. To show our uptime, add these lines:

#!/bin/bash
stty 0:705:bd:0:3:1c:7f:15:4:0:1:0:11:13:1a:0:12\
:f:17:16:0:0:73 < /dev/prolite
echo "<ID01><PU>'uptime' " > /dev/prolite
echo "<ID01><TA>*****U" > /dev/prolite

tail -f -n 1 /var/log/messages |
   awk '{ print "<ID01><PA>" $0 " "; }' >
   /dev/prolite &

The sign can also act as a watchdog for our system by setting up a timer to go off several minutes later. Ideally, the sign will get updated before the timer goes off and the timer will again be set for some time in the future. In the event the sign is not updated, the timer trips and an alternate alert message is displayed.

!/bin/bash
stty 0:705:bd:0:3:1c:7f:15:4:0:1:0:11:13:1a:0:12\
:f:17:16:0:0:73 < /dev/prolite
echo "<ID01><PU><FD>Server Up" > /dev/prolite
echo "<ID01><DTB>" > /dev/prolite
echo "<ID01><TA>00001U" > /dev/prolite
echo "<ID01><TD><FB><CC>Server Down" > \
   /dev/prolite
date "+<ID01><TB>*%H%MD" -date "7 min" > \
   /dev/prolite

To do this relies on some tricks. First, you cannot use a generic timer (<TA>*****) for running standard messages because it conflicts with our watchdog timer. Secondly, we cannot use timer <TA>00000 because it confuses the sign. Thus, we have to use one minute after midnight on Sunday (<TA>00001) in order to display our messages. When no timers are defined, the first timer defined shows our page.

Deleting timer B keeps us using timer A, which shows normal text. The sign ignores requests to delete timers and pages that don't exist. Once page A is defined and displaying, we define page B in the background and set up a time, again using the clever date command to output it seven minutes from now. Since our cron job is set to run this script every five minutes, the timer should never go off unless something is wrong.

If Linux suffers a power failure, the cron daemon is killed, or the sign becomes disconnected, it will display a warning message. The tag <FD> indicates the message should instantly appear instead of scrolling, where <FB> indicates the text should appear from the center—this will get your attention quickly.

More information about the protocol, cable and sign can be found at http://wls.wwco.com/prolite/. This site also includes source code for various applications that manipulate the sign.