Some months ago I ordered a EM-406 GPS module from Sparkfun. I intended to explore geotagging and this module seemed to be a simple one to use : integrated antenna, SiRF III chipset (seems to be well know on forums) while not too expensive.
Among the specs :
- 20-Channel Receiver
- Extremely high sensitivity : -159dBm
- 70mA at 4.5-6.5V
- Outputs NMEA 0183 and SiRF binary protocol
You provide a 5V power source and it begins to output NMEA sentences on the TX output at 4800 bauds. When the led stops blinking the module is fixed : enough satellites are tracked to computes its position as Lat/Long coordinates.
The 1PPS pin provides an 1hz pulse synchronized on the GPS clock signal.
Connecting the module to the PC
Having no serial port on my laptop I use a Prolific PL-2303 USB-to-RS232 adapter. The TTL adaptation is done with a small Sparkfun level shifter board.
One problem is that the serial level is not TTL : 2.8V instead of 5V. Simply connecting the module TX to the level shifter RX-I is not enough. Another level adaptation is done with the following circuit I found after several days of Google fruitless searches : http://www.musicfromouterspace.com/analogsynth/oddsandends.html#GATEBOOSTER [Dead link].
The reverse conversion from TTL to 2.8V can be done with a simple voltage divider circuit.
The power is provided by a spare USB port.
Testing the connection
The simplest way to test if you can correctly read NMEA sentences on your PC is to launch the Terminal configured with the following parameters : 4800 bauds, 1 stop-bit, no parity.
Once powered on the module should immediatly starts the output of NMEA sentences.
Testing the module : SiRFDemo
To go further and actually see the content of the data sent by the GPS module, the SiRFDemo application is very helpful (http://www.falcom.de/support/software-tools/sirf/).
This GPSPassion forum entry provides a lot of information about to the use of the software : http://www.gpspassion.com/forumsen/topic.asp?TOPIC_ID=25575