How to modify a $20 to $59.95 high quality 12 channel GPS for use with any NMEA device. This device
can be found in numbers here at Ebay. It is actually built for a Palm III device, and should
be compatible with palm APRS as is, I just haven't tested it for this.

The Talon GPS receiver is a high quality GPS. It is 12 channel, as most newer
GPS units are. It does not have a battery backup for keeping track of time for
faster initial fixes. To see a review of this unit (actually a RandMcNally
Streetfinder GPS - which yours will basically be after the mod) check out:

RandMcNally Review

Mint box tracker with a palm gps

Mike's GPS mod website

For specifications on the GPS see: http://navman.co.nz/_NAVMAN/land/gps1200.htm

The unit is suceptable to noise. I suspect a lot of this is due to the fact
that there is basically no shielding in the package, except to shield itself
from its own antenna. I think your suggestion of aluminum foil would be a good
one, as long as one can keep the shielding from shorting on the circuit board.

I have not heard too much good about the software that comes with the unit.
I tried to load the software in my Handspring, and had some trouble. Sounds
like others have too. I wouldn't let the software influence your decision (one
way or the other), let it be up to the hardware. And no, the software is not
Linux compatible, but from the reviews I have read of the software, maybe that
is a good thing. The GPS will work with any Linux, Windows, or other software
that is compatible with NMEA.

HACKING INFO:  ===================================================

Buy a RandMcNally GPS for the Palm III from http://www.randmcnally.com

1. Remove the four screws that hold the GPS together. Pull the two sides of
the plastic housing apart. You will find the hook that is meant to hold the
Palm in place will hinder these efforts. Unhook it as you pull the two sides
apart.

2. The GPS circuit board is held on to the sub circuit board by a to the sub circuit board by a 5 pin
header. Since I did not have a big fat solder iron tip, I held my solder iron
accross all five pins, and slowly worked the boards apart slightly. When there
is enough room, bend the circuit boards back and fourth untill all five pins
break. Be carefull not to over stress the circuit board. If you have a better
solder iron, or patience with soaking up all the solder you can easily improve
this method. I then removed each individual pin that was left broken in each
hole.

3. There is a large diode and a yellow capacitor to move from the sub circuit
board to the GPS board. The items are shown in their final position. To better
see where the capacitor is actually connected to see below.

4. Wire power and a serial cable to the GPS board. Remember to ground your
serial cable!

Here is the pinout shown in reference to the above picture:
(I have had many questions about this, so I must not have explained this well. There are 8 pads open on the board. The capacitor goes on the third hole down. The top hole is smaller than the rest. The first two pads are connected and both grounds. You really only need serial out, ground and positive connected. Serial input allows you to send the gps commands, and generally not used, unless you've got your own plans like presetting an initial position - or something of the sort. Many of these pictures can be enlarged by downloading them to your computer -right click mouse, and opening them up in a browser, or photo editing software. That way you can see what I've done a bit better).

o     Ground
O     Ground
O     Capacitor (polarity doesn't matter) - Replaces bare jumper wire
O    (Square Pad) + Positive voltage 4 to 16 volts DC
O    ? Unkown - but not needed for serial com
O    Serial Output
O    ? Unkown - but not ;   ? Unkown - but not needed for serial com
O    Serial Input

And walla, you end up with the finnished product. A 2" by 3" GPS which should
look like:

If you can't figure out something neat to do with your lithium battery, send
it to me and I will put it to good use!

Shield the GPS properly and you should have a lot of fun with this GPS.

Enjoy,

Walter
KD6VYV
http://www.radiohound.com