RS232 led sign


I have an Alpha led sign which has a RS232 (female) connector. I want to connect it to my arduino but don’t know how…

I have bought this thing:
What I have tried is connecting the led sign to a gender changer, a null modem cable, a gender changer, this rs232 board from ebay and then a usb to ttl converter (one that I always use to program bare arduino chips). But this does not work. I also tried it without the null modem cable, same result :frowning:

Does anyone know how to do it proper?


I have a couple of old Alpha LED readerboard signs. I think the interface is really RS485. Maybe. I have a couple of manuals around here somewhere, one is an Operation manual, the other describes all the signals it requires. I'll see if I can locate them.

It has both. This is a picture of the back (click on it to see the big picture):

I am normally using the RS232 port to connect to a pc (the cable has a normal rs232 port on the other end).

I only have this page as documentation:

Which isn't much helpful.

Assuming your using the RJ12 to D-SUB9 connector cable your currently using to connect to the PC then you will need to use either some form of Software Serial or a separate serial port (Mega) if your Arduino is connected to the PC at the same time. Your RS232 converter has 4 pins that need connecting to the arduinos 5V, GND and the relevant RX/TX pins. The protocol looks to be 9600,E,7,1 so this may rule out the use of standard SoftwareSerial library. Both links you supply seem to give comprehensive info on the protocol.
The eBay listing states

Notice:The chip max3232 is made in China,some customer find it not compatible after purchase.

So please make sure the chip is compatible with your own system before purchase.Thanks for your cooperation!

Chicken and egg situation here. :~