Step 5: Modify the USB-TTL Cable for Use with WNR3500L

Take a look at the photo above.  See how each of the leads is covered by a small plastic tab?  Bust out your tiny screwdriver or whatever it is that you have that's tiny, and pry off the tabs on the black, yellow, and orange leads only.  If you choose to remove all six, you will need to wrap up the unused leads in electrical tape to avoid shorting anything out.  I just left the unused leads inside the plastic harness as shown above.  Once you pry the tabs off, the leads that you will use slip out easily. Now, you can plug the cable in.

Step 6: Find Out Where Your USB Cable Can Be Accessed

Open up a Terminal window, with the USB-TTL cable plugged in, and type ls /dev

You should see a screen very similar to what is displayed above.  In my case, "ttyUSB0" is my serial cable device.  If you have more than one of these, unplug the cable, run the command, plug it back in, run the command again, and compare the two lists to deduce which interface is the correct one.

Step 7: Connect the USB-TTL Cable to the WNR3500L

Note: Make sure the router is still powered off and unplugged from power when you do this.  Don't touch anything metal either, don't want to take any risks of shock or shorting anything out, which is always a potential concern when tinkering with open electronics.

This part is particularly important, as if you don't connect these cables properly it will be very frustrating for you!   Take a close look at the photo above.  On the pinout on the board, you will see six pins.  Next to one pin it will read "JP1."  That is actually Pin 6.  Pin 1 is labeled with a "1" next to it.  Connect the cables as follows and as shown in the photo:

Black => Pin 6 (next to JP1)

Yellow => Pin 5

Orange => Pin 2

Note: In this photo, the black and yellow leads are seated properly.  I wanted to show you what an improper cable seating looked like; the orange cable is NOT seated properly.  Make sure all the cables are firmly seated to the pins and that they are not touching each other.

Step 8: Configure Minicom

Now, you'll need to configure and launch Minicom.  To do this, type sudo minicom -s

You will be brought to a configuration screen which will enable you to set the options properly.  Set the options as shown above, using the device ID you discovered in step 6.  After you have set the options, save the setup and exit Minicom.

Step 9: Connect to WNR3500L Via Minicom

Now, launch minicom with sudo minicom

If all is well, your USB serial device should initialize and you will be brought to a blank screen.  Get your hands hovering over the Control-C buttons, power on the router, and IMMEDIATELY type Control-C numerous times.  If you are successful in doing this, you will be brought to the CFE> prompt as shown above.  Type tftpd and go on to the next step.

Step 10: Send the Firmware via TFTP and Reset

Open up another Terminal window and change directory to where the firmware file you will be placing is located.  Then, type tftp 192.168.1.1

**Note for those running Ubuntu 10.10 64-bit** Community member pyroclast notes that it was necessary to set the binary mode prior to put transfer with TFTP (as compared to ascii mode.)

You will be brought to the tftp> prompt as shown above.  Use the "put" command as shown to send the firmware file to the router, and you will be prompted when it is complete.  Don't disconnect any cables while the router is reflashing, and watch the Minicom window to confirm completion.  As always when reflashing a router, perform a full reset when complete.

Step 11: Rejoice and Relax... or troubleshoot

Hopefully, not the latter, but unfortunately things don't always go as planned.  If you're struggling with this procedure, you can post your questions on the public forums or as a comment below!

Quick Links

• WNR3500L Review
• WNR3500L Original Firmware
• WNR3500L Open Source Guide

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