I've searched far and wide and looks like there's conflicting views on what wires to run to the serial port on the wgt634u.

J7:              USB:
  Vcc                1  2   3  4       1: Vcc
  Tx                __________     2: Tx / D-
  Rx               |-*--*--*--*-|    3: Rx / D+
  GND            |__________|    4: GND

1) Does Vcc need to be connected?

2) If (totally hypothetically... no way I did this...) someone mutilates the cell phone pop port before matching up the wire colors using http://pinouts.ru/CellularPhones-Nokia/ … nout.shtml then how does one match the colors up because surely these cheap ebay china things don't remain consistent. - I've tried continuity testing using the USB diagram above, but maybe the circuit needs power or something?

3) How exactly do you minicom into this thing? From what I understand you open up minicom in linux, set it to use 115200 8N1, switch from hardware to software flow control - then hold down Ctrl+C while you power cycle the router. Yes? No? I used http://www.nslu2-linux.org/wiki/HowTo/AddASerialPort as a reference but couldn't get anything above 1V (just having the USB plugged into my laptop and the other end stripped and hanging so I could use a multimeter on the various wires)

4) Is it possible my DKU-5 is fried?

(Last edited by bradkarhu on 26 Jan 2007, 22:16)

I'm not sure what the diagram above means. There are no Tx/Rx lines on a USB bus. If you have a DKU-5 (clone) cable for Nokia, there is a USB-to-serial convertor embedded in the USB plug. The colors of my DKU-5 cable, at the GSM side of the cable are:

pin signal                           color
--- ------                           -----
3   ACI (insertion/removal detect)   orange
4   VOUT (+/- 10mA)                  green
5   N.C.
6   RX (PC --> phone)                white
7   TX (phone --> PC)                blue
8   GND                              black

And yes, the converter needs power to operate, so you need to connect VOUT (green) to the 3.3V output of the router.

I went ahead and got another DKU-5 off ebay and this time carefully examined it. Here's my findings:

Pin 2 = GND (white)  - mine didn't have a Pin 8
Pin 4 = Vout (green)
Pin 6 = Rx (orange)
Pin 7 = Tx (blue)

Even then when I tried minicom it didn't work. After a while I tried screen and it worked perfectly right away.

command: sudo screen /dev/ttyUSB0 115200

So chances are my first cable was fine. Hopefully this will help someone that might have the same problem.

I always use screen, it's just quicker to work with. minicom should work too though..

I find a (small!) speaker helpful for finding which pin is tx on a device if I forget or it's unknown/not clear

I do it the lazy/dangerous way -

The pl2303 chip doesn't require additional power so the only pins you need to hook up are rx, tx, gnd; you can skip vcc.

If you connect the rx pin to the gnd or tx you'll probably get a few characters of line noise. If the rx pin is connected to the tx pin, then anything you type into the terminal application will be echoed back to you. So, just by playing with the wiring on the cable you can usually figure out the pins.

I have been meddling with this issue: I bought a CA-42 cable.
(1) Using a multimeter, I was unable to get voltages > 0.25. This supports bradkarhu
(2) I have 5 colours: black, green, white, blue, orange.  Both blue and white when touched to the 3rd pin from J7 get feedback from the wgt634u. What is this all about?
(3) Using the approach of mbm, when I try attaching different wires together, I never get text echoed back. Do I need to set a specific bits per second speed??

Not all DKU-5 cables use the pl2303 chip, and even if they do, they might need power. My cable (KQ-U8A) uses an ark3116 chip, and definitively needs power from the GSM-side to operate. Without power, you will not get an echo when you connect rx and tx. I found a list of DKU-5 cables here.

Are you sure?  I have an ark3116 cable that only needs Rx, Tx and GND connected to the router.
I would imagine most if not all USB adapters pull power from the USB port.  It doesn't make sence to pull it from anywhere else.

I'll post the pinout of my cable when I get home.
It's an Insten cable just like this one but was much less expensive.

I think it makes sense to power the chip from the GSM. That way there will be no signal on the input of the phone when it is powered down. In general, chips don't like voltages above the power supply, and may be damaged by it.

I bought my cable from emarket888_de on eBay. I'm not sure if he is still selling the same cable, though.