Currently, I am lugging around my USB to Serial cable (since my laptop does not have a serial port), a Cisco console cable, and a null modem cable (for older switches and other equipment). When I work on older equipment, I have to unplug my Cisco console cable, find my null modem cable, and then plug all of that in.
Wouldn't it be easier if I had an adapter that I could carry around instead of switching cables? Or better yet; maybe I could make a bunch of these cables and keep them plugged into what few older switches we have left.
I know there are probably adapters out there already, but I did not want to purchase anything. I figured making one would be easy enough. Especially since I had about a billion console cables in a box from all the Cisco stuff we ordered (better to reuse than hitting the trash can). So I grabbed the parts and headed to my workbench.
Step 1: Parts and Tools Needed
2 Cisco Console Cables
1 RJ45 Network Jack
Scissors, knife, or cable cutters (or all three... the shielding is tough!)
Punch down tool (unless you have an RJ45 that does not require a special tool)
(OPTIONAL) Multimeter to test the pinouts
Step 2: Cut the Second Cisco Cable
Get out the scissors and cut the second Cisco cable in half. You can take the end that has the RJ45 jack on it and throw it in a safe place for some other project.
We are going to use the section of cable that still has the 9 pin adapter on it. Take the end of that cable and strip the wiring about half inch down.
Step 3: Wire the RJ45 Jack
Now comes the tricky part. We need to match the wiring in the jack to be configured for RS232 null modem with full handshaking. I found this page very helpful when I was wiring: RS232 serial cables pinout
Some colors might vary on the Cisco cables (I checked the pile we had), but not much. White and gray are the only colors that I noticed changed in my stack of cables. You might want to grab your trusty multimeter and test the cables for your pinout diagram.
See the wiring chart picture for details.
Step 4: Finished!
Once the cables are safely wired into the RJ45 jack, simply connect the first, untouched Cisco Console cable into the jack. TADA! You now have a quick and easy cable that can be used as both a Cisco Console cable or a Null Modem Cable!