Making your own console cable

Many of the Siemens mobile phone data cables contain USB->Serial converters, to talk to the phone using 3.3v serial signaling. These cables generally contain CP2101 (obsolete) or pl2302 (much newer, better performing) USB->Serial converters, and only cost a few euros. Look on Ebay for the cables which either have a box half-way along the cable length, or an oversized USB connector which contains the necessary logic.

Cable looks like:

You will need a volt/resistance meter. The wires are colour-coded, but often inconsistent between cables.

- Cut off the mobile phone connector on the end of the cable and strip out the wires.

- Locate the GND wire by checking resistance between each of the wires and the USB shell

- Plug the USB connector into your Linux system and start minicom. Set a low Baud rate (9600). Connect your voltmeter between GND and each other wire in turn. For each wire do the following: Hit and hold the SPACE bar. If you've found the TX wire you should see a noticable drop in voltage when holding the space bar down. Why? The binary for SPACE is 00100000, which is a lot of 'zero's. Since rs232 lines are high when not sending signal this means when you keep sending space the average voltage will be noticeably lower than when you're not sending it.

- Finding the RX line is now easy. Connect the TX line to each of the remaining line in turn - when you've found the RX line you should see characters echoed back to the minicom screen when you type, because you have established a loop-back from TX to RX.