Product Review: Pro-Lite Scrolling Message Signs

The Pro-Lite Tru-Color II PL-M2014R is an affordable multi-color LED scrolling message board that is capable of being controlled by a standard RS-232 serial port. The sign is obtainable from Pro-Lite directly (http://www.pro-lite.com/), but can also be purchased at various discount warehouses for approximately $150. The serial cable and Windows software are sold separately.

This article is not just a review; it can serve as a primer for Pro-Lite's PL-M2014R with ROM release 5.24Q and 32K of memory with Trivia mode, basically your standard sign. Until now, not much developer information has been available to the public, meaning signs were usually configured with the included infrared remote control to display static messages. For very little money, it is possible to build your own serial cable and control the sign using Linux to display more than static text.

The business and personal applications for a highly visible sign are almost limitless: reporting days until software delivery, announcing traffic congestion, providing the weather, showing the date and time, sending public messages, reporting system load, announcing new mail, showing who's logged in, warning when disk space gets low, login information, announcing unexpected server outages as a watchdog, etc.

Communicating with the sign is almost as simple as beaming text out the serial port; however, a bit of text manipulation is necessary in order to get the sign to respond and do advanced tasks. Linux handles the serial port communication, so sending information to the sign appears as trivial as writing to a file.

Luckily, the majority of the work can be accomplished by simple scripts. All you need is a basic understanding of the shell, AWK, PERL or Python, and you can be running in almost no time. The first hurdle is to build a cable and configure Linux to talk out the serial port.

Figure 1. Female DB9 Adapter

The first step is wiring an RJ12 to female DB9 adapter. It requires no tools, and an adapter kit can be purchased at most computer supply stores for about $2 US. The only other thing you need is a length of RJ12 cable with male adapters at each end. This means a standard telephone cord will do nicely. Your cable will most likely have the standard colors black, red, green and yellow, in that order.

Cables come in two flavors: straight-thru and reversed. You'll need to take the RJ12 cable and put it end to end (like a loop) to find out which kind of adapter you need to build.

Figure 2. RJ12 Adapter Diagram

One of two things will be noticeable: either the wires will match black to black, red to red and so on, or they will reverse their order showing black to yellow, red to green and so on.

If the cable is a straight-through, where the colors match, wire your RJ12 to a DB9 adapter using Pin 2 as green, Pin 3 as red and Pin 5 as yellow. If the cable is reversed, then where the colors reverse sequence, wire your RJ12 to a DB9 adapter using Pin 2 as red, Pin 3 as green and Pin 5 as black.

Figure 3. RJ12 to DB9 Wiring

Shove the unused adapter wires into the casing and snap the adapter shut. Take care not to let the exposed ends touch anything metal inside the adapter casing. You may want to clip the unused wires. Put an extension cable on your serial port and connect the adapter wires directly to the extension cable in order to test the wiring configuration before pushing the pins into the connector.

When all is said and done, one end of the RJ12 goes into the side of the LED sign, the other into the adapter you just made, and the adapter plugs into the computer.

My sign is plugged into COM1, also known as /dev/ttyS0. I've elected to use a symbolic link to the sign, in the event I ever decide to change to another serial port in the future. To make the link, as root type:

ln -s /dev/ttyS0 /dev/prolite

I tend to shy away from doing development as root. Putting security issues aside for the moment, we can make the device world-writable by typing:

chmod a+rw /dev/prolite

In theory, the sign requires a 15ms delay between each character sent to the sign. I've found that Linux's device driver seems to work just fine without having to do anything special in the software.

stty speed 9600 cs8 -parenb -cstopb cread \
   -clocal -crtscts -ignpar -echo nl1 cr3 < \
   /dev/prolite

Naturally, you can substitute any baud rate the sign will handle for the 9600. This command will work when you aren't root because it is world-writable.

The most important piece of information for communicating with the sign is that each command sent to the sign must end with a carriage return/newline pair. This is ctrl-M ctrl-J on the keyboard or 0x0C 0x0A in hexadecimal. C programmers will recognize it as \r\n. If you want Linux to handle the end-of-line sequence for you, type the command:

stty opost -ocrnl onlcr < /dev/prolite

When you send a newline, Linux will send both carriage return/newline automatically. Text can now be listed or redirected to /dev/prolite from the shell. If you want to send the carriage returns yourself, type:

stty -opost -ocrnl -onlcr < /dev/prolite

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

stty 0:700:bd:0:3:1c:7f:15:4:0:1:0:11:13:1a:0:
12:f:17:16:0:0:73 < /dev/prolite