You say that you figured out the RS232 protocol and are able now program the sign without their software. However you then go into a dialog about how their software does not have an option to open a file. Why would you care about that if you do not need to use their software?

Please explain that detail better.

You may be faced with having whatever device is hosting the RS232 port end of the sign interface also provide an emulation of the IR remote. This could be a software driven IR transmitter diode that is driven so as to produce the same 36/38kHz modulated carrier as the existing IR remote. Alternatively you could go into the sign logic board and wire in a hardwire connection into the place that their IR receiver module normally connects. You may be able to connect directly in as a wired-or connection since many IR receivers are also open drain / open collector outputs. If you do the wire-or connection you may want to cover the IR receiver with black tape to prevent stray IR signalling from corrupting signals that you would inject on the hard wired connection.

Note that signalling on the hardwired connection would normally be the equivalent of the IR signal modulation envelope with the 36/38 kHz carrier removed. Virtually all IR receivers remove the carrier within the receiver.

Michael Karas