Amateur Radio WB3GCK Poqet PC Plus
Serial Port Adapter Cable

Craig LaBarge, WB3GCK

When I had the chance recently to pick up a "new-in-the-box" Poqet PC Plus, I jumped on it. I had picked up one of the original Poqet PCs (Model PQ0181) a few years earlier and had been using it for packet radio and logging. I was looking forward to the additional features and power provided by the PC Plus.

One drawback with the Poqet PC Plus is that it uses an unusual, 26-pin, miniature connector for the serial port. So, unless you have some way to convert to a standard DB-9 connector, the serial port is useless.

The original Fujitsu adapter cables are extremely rare and it is next to impossible to find one for sale. The mating connector (Model TX20-26P-D2LT-1A1) made by JAE is only available in lots of 50 with a 12 week leadtime; not too good when you only need one connector. The good news is that Poqet was not the only manufacturer to use this unusual connector.

It turns out that Toshiba used this type of connector on some of their laptops to interface to external floppy drives. If you look around at hamfests, flea markets, or on eBay, you can find a Toshiba floppy drive bay for a few dollars. They come with a 7 inch cable which is terminated with the connector you need for the Poqet PC Plus. I wish I could be more specific as to the model numbers of the appropriate Toshiba devices, but I can't. The one that I found on eBay was marked only as "FDD Attachment Case."

So, assuming you've located a Toshiba floppy drive bay with the right connector on it, here's how you can turn it into a serial port adapter cable for your Poqet PC Plus.

  1. Cut the cable off of the floppy drive bay as close to the case as possible. This will give you about 6 or 7 inches of cable.
  2. Strip off about 1 inch of the outer jacket of the cable and remove the braid shield.
  3. Strip about 1/8 inch of insulation off of each of the 26 wires.
  4. Determine the pin orientation on the connector. Looking at the rear of the Poqet PC Plus, the 26-pin serial connector pins are arranged as follows:

    Poqet PC Plus Serial Ports

    Now you can determine the corresponding pins on the connector on your cable.
  5. You now need to figure which wires correspond to pins 2 through 10 on the connector. This is a bit tedious, but doesn't take too long. Use an ohmmeter to check each wire. When you find wire corresponding to pins 2 through 10, note their colors. The table below shows the colors I found when making my cable. Your mileage may vary.

    Function DB-9 Poqet PC Plus Wire Color
    TXD 3 2 Orange/Black Stripe
    RTS 7 3 Gray/Red Stripe
    DTR 4 4 Gray/Black Stripe
    GND 5 5 White/Red Stripe
    RXD 2 6 White/Black Stripe
    CTS 8 7 Yellow/Red Stripe
    DSR 6 8 Yellow/Black Stripe
    DCD 1 9 Pink/Red Stripe
    RING IND 9 10 Pink/Black Stripe

  6. Now that you've identified the wires you need, cut the remaining wires back as far as you can. Be sure that none of the unused wires are shorted together.
  7. All that's left is to solder the 9 wires to the DB-9 connector. Use the table above as a guide. For the DB-9 Male connector, I used a Radio Shack #276-1537C connector and a #276-1513 backshell.
  8. Double check all of your connections and you're in business.

73, Craig WB3GCK

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