Building a serial cable for Netgear WGT634U

If you are reading this, you are probably the kind of person that cannot resist the urge to mess around with your AP, router and the like.

So you inevitably end up with a lot of elegant bricks that are sitting in every corner of your room and from time to time you try to revive them in every possible manner.

I recently bricked my Netgear WGT634U (see this other post) and in order to revive it, I had to build a serial cable to connect to it.

After some googling, I found an interesting post (https://forum.openwrt.org/viewtopic.php?id=9453) which put me on the right way to build a usb-to-serial cable using stuff that I already had sitting in a closet of my room.

More googling and I got to the CFE prompt of the unit, which later allowed me to revive it and have another wonderful OpenWRT device in my network.

Here is how I did it:

  • take an old CA-42 Nokia cable (also DKU-5 cables are reported to work). I received mine with an old Nokia mobile. These old cables contain an usb-to-serial converter built-in, right inside the USB connector. No need to buy an expensive USB-to-serial converter any longer! These Nokia cables are really cheap and can be found anywhere.
  • cut the cable in half.
  • take the half of the cable with the Nokia proprietary connector (it’s called POP port) and check with a multimeter the mapping between the pins on the POP port and the five wires on the other side of the cable. In particular we are interested in the wires connected to pins numbered 8, 7, 6 and 4.
  • The nice guys at nas-central tell us that the mapping is as following: CA-42 pin numbering
    • Pin 8: Ground
    • Pin 7: TX
    • Pin 6: RX
    • Pin 4: +3.3 Volt
  • Write down the association between color and type of signal. Here is an example (HINT: every cable has a different color mapping so don’t trust any mapping you may find on Internet, you have to find the correct mapping by yourself)
    • Ground: black
    • TX: blue
    • RX: white
    • +3.3 Volt: green
  • Throw away the half of the cable with the POP port, take the part with the USB connector
  • Find an old floppy connector – it has 4 pins and it fits into the serial connector on the Netgear WGT634U
  • Connect the wires in the following order: +3,3 Volt, TX, RX, Ground
  • As you can see from the picture, the serial connector is perpendicular to the lan ports. Locate the pins of the connector and the respective signals: wgt634u PCB
    • +3,3 Volt (on the side near the lan ports)
    • TX
    • RX
    • Ground (on the side near the leds)
  • Connect the cable to the Netgear WGT634U, make sure to match the signals

That’s all! Fire up minicom -s and setup the port: /dev/ttyUSB0 , 115200 8n1, hardware flow control off, software flow control off.

Power on the Netgear WGT634U. Thumbs up :-)

Caveats:

Recent Nokia cables don’t have a usb-to-serial converter built-in and won’t work. You can recognize them because the USB connector is much smaller. You have to make sure that the USB connector is bulky.

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8 thoughts on “Building a serial cable for Netgear WGT634U

  1. Secondo me sì! Se la descrizione del venditore ebay è accurata, quello è il cavo giusto.
    Mi raccomando per mappare i pin usa la procedura che ho descritto nel post, non ti fidare degli schemi basati sui colori che trovi in giro.
    In bocca al lupo :)

  2. mi è arrivato il cavetto, il router ancora no :(

    ho già provveduto alla mappatura dei segnali, spero in modo corretto, ma non so come verificare ulteriolmente la cosa.

    ground e 3.3V dovrebbero essere corretti, ho verificato direttamente con il tester.

    a riposo, rx e tx sono anchessi fissi a 3.3V, sapresti consigliarmi un metodo per verificare la corretta mappatura di questi, magari utilizzando minicom e simili?

    LP

  3. se hai un vecchio modem seriale puoi provare a collegarti a quello e vedere se prende i comandi AT. O in alternativa puoi provare con qualunque device seriale tu abbia.
    Boh, è l’unica cosa che mi viene in mente…

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