ALPHA 215C Data Cable ConstructionDisclaimer: This information was produced via trial and error with an ALPHA 215C sign. I have not tested it with a BetaBrite sign.
To start with, I puchased a DB9F to RJ12 Adapter Kit from MicroCenter for $1.99 US; part number G243BU (BU means blue, where red ones are RD). The part is made by Advanced AESP.
Using a Cross Over CableYou'll need a cross over RJ12 cable (six wires, standard telephone cord won't do). Hold it end to end and verify that the colors do not reverse order. This means that pin 1 maps to pin 6, etc.
Construct the cable so that:
It is very important that the adapter's wiring match your RJ12
cable. If you have a straight through cable (the colors run the opposite when
put end-to-end) the adapter will not work. In that case, you should wire
Pin 4 of the RJ12, the red wire, goes to Pin 2 of the DB9 (RX).
I highly recommend you test your wiring before snapping wires into the DB9 female recepticle. Removing the wires, which typically requires a pair of needle nose pliers, can (and does) damage the adapter.
You might want to take a look at how I do my trial and error to build and validate a cable.
Be sure that the "free" wires are not touching each other, or the RJ12 pins, when you shove them into the case to snap it shut. Insulate well. If your sign starts making beeping noises when you plug it into the computer, then you have wires touching and this is bad.
Once you have the adapter, plug one end into the computer (optionally using a regular RS232 extension cord), and one end of the RJ12 into the adapter and the other into the sign.
I was only successful in communicating with the sign when using the
RJ12 connector on the right. Additionally, if there was longer than
a second between keystrokes, the sign didn't respond. As such, I
couldn't get the sign to respond using a terminal emulator because
I was too slow at typing. I was forced into writing a small app that
beamed chunks of bytes to the sign at a time.
Back of the ALPHA 215C led sign.
This wiring is slightly different than the wiring diagram for the Pro-Lite cable, which will not work with Alpha signs.