General GPS project notes
I currently have three OEM GPS modules to play with. The Trimbles are 8 channel. (There is a pin compatible Lassen iQ that has 12 channels, might try one of those later).
The Garmin is 12 channel. The Trimbles are interesting because they can generate TSIP output which I can post-process in Pathfinder Office. The Garmin is interesting because I can try collecting RINEX data and postprocess that.
I have external antennas for all three. All three are similar in that they produce a datastream on a TTY signal level serial port, so I need to interface to that. My intention is to do things in 2 stages; first build a generic board to take serial data out to an RS232 port connected to a computer then to build a PIC based datalogger/interface to manage the GPS and talk to a handheld device.
At the PIC stage I want to use a Bluetooth module on the serial port so that my Dell Axim can talk to it without having any clumsy cable connection.
Garmin
Trimble
Lassen
Serial interfaces
Serial TTY to RS232
Serial TTY to Bluetooth
Serial TTY to USB
Should I get tired of how easy the RS232 and Bluetooth options can be, I might want to try USB.
PIC datalogger
Power supply
High efficiency switching voltage regulators National LM2597 3.3 and 5.0 "Simple Switcher" 8-DIP $3.78 Digikey
Requires 1N5817 Schottky diode and 100 uH inductor (M9799-ND) and the usual handful of caps.
Backup / standby power
Button cell batteries - CR2032
