Instructables

Retractable null modem (RS-232C) cable

Picture of Retractable null modem (RS-232C) cable
RS232_10.jpg
Are you tired of never having a null modem serial cable when you need one...or tired of carrying around a bulky cable? I was, so I made one out of a retractable phone cable that I can easily carry in my pocket or toolkit.

By null modem cable I mean, female-to-female serial cross-over cable that uses DB-9 connectors. They use the RS-232C protocol. I mostly use null modem cables to upload firmware to TVs..and control them. Most TVs that have a RS-232C (Serial) port can be controlled using telnet (Like a wired remote, but more powerful).

I had a couple of retractable phone cables in the bottom of my drawer at work I thought I'd never use again, but I kept them anyway. As I was looking at them trying to figure out what I could do with them, I remembered that the RS-232C instructions in LG TV manuals say you only need 3 wires. I looked at one of the schematics and sure enough, inside the TV only the 2, 3, and 5 pins are connected. So I knew a retractable phone cable or Ethernet cable would work.

This will only work if your RS-232C devices use 4 or less wires. I haven't seen a retractable cable with more than 4 wires, but they may exist.

The second picture just shows two other types of retractable phone cables. I paid less than a $1 each for those. The wires in those are really small and hard to work with, so use the type I use in the instructions if you can.
 
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Step 1: Needed Tools

Picture of Needed Tools
Here are the main tools you need. Radio Shack number for the D-Sub connectors is 276-1428. The D-Sub Hoods is 276-1513. They have several different hoods at the shack, any will work. But..Avoid the metal ones, they're too heavy. You could even make your own hoods, just make sure you have something good to grab onto when removing the connectors from a device.
derpityderp3 years ago
It's a great idea, but a lot of wasted work. Just Google "RJ45 to RS232" and you find items like this: http://www.gwytech.com/shop/images/uploads/RS232-RJ45.jpg then just connect it to a retractable Ethernet cable.
fosin (author)  derpityderp3 years ago
Those aren't Null Modem. You'd still have to take them apart to cross-over 2 and 3. This is easier and local sourced parts. What you linked to is the exact reason i started making these and giving them out to people. We got tired of using those.