DB9 serial break out cable.

Back in the old days of eight bit computers such as the Commodore 64, Apple, TRS-80, and the Atari among others, the only way to transfer data between computers was either a modem or a much coveted rs232 interface. There was no ethernet, usb, or wifi. Today things have changed a lot but you still need to know about the rs232. Typical situation. You need to flash a router with the latest firmware as it does not support the good old web upload.
i.e. :  http://romain.novalan.fr/wiki/Flash_Fonera_2100_with_OpenWrt_by_console_port_and_redboot

We have already done parallel breakout cables. (http://www.instructables.com/id/No-solder-parallel-port-break-out/) and I have eluded to a joystick port break out cable. Now I would like to do a serial port cable. Why? I have been finding more and more aricles about interfacing to the serial port. Everything from temperature sensors, radio transmitters,  and even used just for power. You could also use with with the appropriate electronic parts to be a jtag cable.

Notice: Try this at your own risk. I will not be responsible for any issues. If you are unsure, get a professional to help.

Note: bc547=nte123ap bc557=nte159

Step 1: All serial voltages are not the same.

There are 3 basic voltages for serial that are used. They are 12,5, and 3.4 They could be even some other voltage. You have to check the documentation of the devices you are using to be sure. Maxim and other companies make integrated chips to make the interfacing easier. You can also make you own circuits from discrete parts. There are a ton of schematics on the internet to choose from. If you are unsure get a professional to help.

With all kinds of usb interfaces about, it seems like there is a usb for everything. With the increase in the need to attach to micro-controllers routers and other flashable hardware, it does not hurt to get to know the rs323 port.  Pinout's are usually documented. You have to be careful though, because you have to know what voltage you are working with. 12, 5, and or 3.3. Maxim and other companies make special chips to make this easier. Epanorama.net has some good information also.