Intro, transferring the GPS-module


The GP2X is an handheld running Linux. It has 2 arm-processors and a few peripherial interfaces: Available on the ext-port is a serial port which normally is used as a debugging port. Other hardware can be connected to it too, though. I've used it to build a GPS-receiver into the GP2X, while keeping the original debugging-function.

The beginning

It all started when I saw a SDIO-GPS-card in the sale-basket of a local computerstore. The beastie was only E49,-, which isn't too expensive, and it came with an internal antenna and an external antenna with 5M coax-cable. Even if the device itself wasn't usable, I always would have 2 nice GPS-antennas.

Opening the device

As soon as I came home, I decided to void the warranty and open up the device. The contents were as I hoped: the device was made of a SDIO-to-serial-port-device and a generic (but tiny!) GPS module with a serial port at TTL-levels.

After a bit of measuring, I found out which of the connections was the gnd, which one was the +3.3V and which one carried the signal. I then decided to test my findings and connected the thingy to the computer.

The weather was nice and I picked up about five sattelites: the device seemingly worked the way I thought it would.

Into the GP2X

From my experiences with the USB-port I built into my GP2X, I knew the unit still had some spare room to put things in. I opened my GP2X and found myself a nice location for the GPS-pcb:

I then started connecting wires. I'd only need three: power, ground and serial. The serial pin was available as a via at the underside of the PCB:
The gnd and 3.3V is retrievable at U13, pin 7 and 14 respectively. After connecting everything and booting up the GP2X, it worked!

I got some serial output too:

The serial output is damaged a bit, because the gp2x-menu tries to read from the serial port, too, but the NMEA-strings are recognisable.

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