Linksys WRT54G/WRT54GS Dual Serial Port Mod

This page contains instructions on how to add two serial ports (one DB9 Female DCE port and one DB9 Male DTE port) to a Linksys WRT54G (version 2 hardware) or Linksys WRT54GS wireless router.

THIS WILL VOID THE WARRANTY ON YOUR ROUTER.

The DB9F (Female) connector on the front is wired as a DCE (think of this as a peripheral serial port), and can be connected directly to the serial port on a host PC. This gives you access to the built-in serial console on the router (115200, 8, N, 1).

The DB9M (Male) connector on the top is wired as a DTE (think of this as a host serial port), and can be connected directly to peripherals like an external serial modem, or other serial devices which are normally connected to the serial port on a host PC.

The pinout of JP1 on the Linksys PCB is as follows:

Pin  1: 3.3V        Pin  2: 3.3V
Pin  3: Tx (ttyS1)  Pin  4: Tx (ttyS0)
Pin  5: Rx (ttyS1)  Pin  6: Rx (ttyS0)
Pin  7: NC          Pin  8: NC
Pin  9: GND         Pin 10: GND

Note that neither of the serial ports support hardware flow control (it's not pinned out on JP1 on the Linksys PCB), so you need to use software flow control when connecting to these ports.

Linksys WRT54G/WRT54GS Dual Serial Port Mod

Requirements

Remember, this will void the warranty on your router. I take no responsibility for your actions.

Instructions

  1. Open up your wireless router. This step will void the warranty on your router. I used Void Main's instructions (the picture is linked from his site, and those are his hands, not mine).

    Opening the case (picture courtesy of Void Main)

  2. Solder the 10 pin IDC male PCB-mount header at JP1 on the board, as shown below. This step will *really* void the warranty on your router. This is the only soldering you need to do on the Linksys PCB. You might like to re-assemble your router and test it out just to check that it still works after this step.

    10 pin IDC male PCB-mount header soldered at JP1

  3. Build up the AD233BK kit as per the instructions provided with the kit, with the following modifications:

    AD233BK PCB Layout

  4. You can either solder the included DB9F PCB-mount connector onto the board (and mount that to the front of the case), or do as I did and extend the connections using wires to allow a new DB9F connector (the kind which is normally connected to the end of a cable instead of mounted on a PCB) to be mounted through the front of the case with the metal plate on the front covering the ugly hole.

    I found the best spot to mount this connector is right where it says "Wireless-G Broadband Router" on the front of the case. Use the holes in the case a a guide (they line up exactly with the mounting holes for the DB9F connector)

    I left the connections between the AD233BK PCB and the DB9F connector to last (just before closing up the case), and it was a bit tricky but worth the effort to get a good looking finish.

    Front DB9F connector mounted through the case

  5. The wires for the second serial DB9M connector are soldered to the right-hand pin of J1 (RXD - the white wire in the picture below), the left-hand pin of J2 (TXD - the yellow wire in the picture below) and GND (I used the grey wire which you can't see under the white and yellow wires, and connected it through left-hand pin of J1 and then shorted it to GND on the underside of the PCB). The blue wire which you can see in the picture is not connected to anything in particular (I tied it off using the right-hand pin of J2).

    Top of PCB showing DB9F extended using wires Bottom of PCB showing DB9F extended using wires

    The second serial DB9M connector (which I mounted on the top of the case) is connected to the other end of the wires as follows:

    Front DB9F connector mounted through the case

  6. Crimp some cable into the 10 pin IDC female cable-mount header (make sure the wire marked in red is orientated to pin 1 which is normally marked with an arrow), and wire it to the AD233BK PCB as follows:

    Female IDC connector plugged into the main Linksys PCB IDC cable connections to the AD233BK PCB

  7. Mount the DB9M connector on the top of the case, plug the 10 pin IDC female cable-mount header into JP1 on the Linksys PCB, and solder the wires through the front of the case onto the DB9F connector.

    Final assembly #1

    Final assembly #2

    Final assembly #3

  8. Double-check all connections, and then re-assemble the router case.

If you find any ambiguous or non-obvious instructions on this page, or have any trouble at all in following the instructions, then please let me know.

Did I mention that this will void the warranty on your router, and that I take no responsibility for your actions? Sure I did. Don't bother sending your legal folk my way ...


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