A few months ago, I found myself needing a null modem cable to connect to a server, the Dell Poweredge R810. I had to figure out why it wasn’t booting (a RAID issue). At the time I didn’t have a VGA cable for video out, but luckily I did have a regular straight through serial cable and an RS232 gender changer that I use for other devices. Getting it to work as a Null Modem cable was a simple matter of wiring three connections.
I used three wires from my Arduino. I was trying to avoid splicing wires, so this was perfect.
The only three wires you need are receive, transmit, and ground (2,3, and 5 respectively). In the above, the transmit and receive wires were connected correctly on one end, then on the other end I reversed transmit and receive and ran 5 normally.
These wires weren’t held in place. The pins on either end gave enough friction to hold them in, although tentatively.
Here is the final “product” in the back my R710. Yes, I know there is a video cable here, but when I originally needed this, I had no video out.
If I didn’t already have a straight though serial cable, I would have just wired something by hand to go from serial to serial (instead of the USB serial adapter).
In the case of Dell Poweredge servers, iDrac Enterprise cards are a better option for management (especially remotely) but serial cables are still great for connecting to other devices.