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Building a Cable to Debrick La Fonera WIFI Router

Well, all great minds screw up once in a while. I was thrilling away with my La Fonera 1.0, freshly hot-rodded with FreeWLAN v0.9.2, when the Fon came to a screeching halt! I was trying to do something Really Cool, and set it up as a Transparent Ethernet bridge. In this mode, the La Fonera would work as a wifi client device. The WAN Ethernet port would be repurposed as a LAN port, which would be bridged to the upstream LAN and DHCP server. This way, I could turn my tiny USB-Ethernet print server into a wireless one.

Well, it turns out that FreeWLAN’s QRM implementation isn’t quite working perfectly. To make matters worse, I can’t just hold down the ‘ole reset button because that button is ignored until the firmware finishes booting and polls it! This La Fonera isn’t finding the WLAN I configured it to join, so it isn’t setting up it’s virtual interfaces. I’m told that it’s stuck in this incompletely booted state forever. All I can do is ping it under very particular circumstances. No SSH, and no web admin exist any more.

Proponents of FreeWLAN advise flashing the kernel ASAP with one which allows reflashing the firmware over the Ethernet cable. I have done this before, when I was using DD-WRT for the La Fonera, but had not yet done it with this particular router. This leaves only flashing by serial connector. This is often referred to as a “JTAG” connector, but technically the La Fonera just has a serial connector that is simply at a lower voltage (TTL) than the serial port (RS232) you may have on the back of your PC. This requires a voltage-level adjustor. The folks at FreeWLAN were very helpful in providing me a list of options, and I decided that I would build the serial adaptor myself.

CLICK ANY PICTURE BELOW FOR LARGER IMAGE

La Fonera 1.0 (FON2100) (left), (right) La Fonera 1.1 (FON2200)

The popular design utilizes a Maxim 232 or 3232 integrated circuit. Maxim will provide free samples of this part, with free shipping from their website. I ordered two, which arrived about a week later.

I went to Radio Shack, our local overpriced electronics parts store, for 5 polarized tantalum capacitors, a small breadboard, and a 9-pin female serial connector. The bill came to $12.91 with tax.

I used sections of an old floppy cable for wire and for the connector to the La Fonera, as the holes were exactly right.

As luck would have it, the first one I built didn’t work properly. On my first trip to Radio Shack, I had bought slightly cheaper nonpolarized electrolytic capacitors. The MAX3232 datasheet said that nonpolarized would work, but perhaps that is not so for this particular project. I’m happier with the way the much smaller tantalum capacitors look, anyway.

We have RedBoot!

Also, if I let it boot up uninterrupted, I can hit ENTER for a telnet session to the OpenWRT firmware which the fonware is based on:

Next up is flashing the CAMICIA edition of the linux kernel which permits access to Redboot over the Ethernet port. I may choose XMODEM to transfer files while connected to the serial port. Then i’ll switch to Ethernet to more quickly flash the 0.7.1 edition of fonware which works best with FreeWLAN. Switching to wifi, I’ll manually configure fonware to download FreeWLAN right away, before I ever connect the Ethernet to the Internet, preventing further fonware updates. Fonware updates get slipstreamed into future FreeWLAN editions, and thus the router really does stay up-to-date.

3 Responses to Building a Cable to Debrick La Fonera WIFI Router

  1. Manny says:

    Do you have a better picture or diagram as I have all parts but am using a small solderless breadboard and I can’t get it to work. I need to know where on the breadboard all the wires connect and all capacitors go. I have the DB9 female already made. Thanks a lot if you can help here is my e-mail. atesfaye@yahoo.com

  2. austintx says:

    Manny, under the second picture is a link to the diagram you want. Look for blue text in the blog; these are clickable. 😉

  3. donito says:

    Can you use nonpolar ceramic capacitors instead of tantalum? Or will I run into the same problems you had using nonpolar electrolytic capacitors?