help about GPS

ROBOTICAR · Joined: 28 Aug 2007 Posts: 45

I want to begin a project with gps. but I don't have any information and experience . I want to know:

what's the data out put form GPS module ?
I want to show the special place in color glcd.
how can I do that?

thanks

jma_1 · Joined: 08 Feb 2005 Posts: 147 Location: Wisconsin

Howdy ROBOTICAR,

Many of the GPS receivers on the market use RS232 and/or bluetooth. The protocol usually follows the NMEA 0183 spec. If you like CAN, there is even NMEA 2000. The NMEA 2000 receivers are harder to find and not as prevelent.

The simplest approach might be the RS232 interface from a GPS receiver to the PIC. The protocol is simple and comma delminated. Separate messages are sent for speed of ground, course over ground, lattitude, longitude, time, etc. A few companies even make PC simulator software.

I do not have a suggestion for the color lcd. I have seen ads for earth lcd products and the seem interesting, but expensive. The last one I looked at had an Atmel uP and might elminate the need for the pic ;) I personally think it would be more fun to build your own board and LCD interface, but that is just me.

Cheers,
JMA

jma_1 · Joined: 08 Feb 2005 Posts: 147 Location: Wisconsin

Greetings ROBOTICAR,

I forgot to post RS232 characteristics.

4800 baud, 8, N, 1
variable length sentences (82 between start and end deliminators?)
comma deliminated
checksum optional -> indicated after '*' in protocol
start character '$'
ends with <CR><LF>

example:
$GPVTG,291.6,T,295.0,M,000.2,N,0000.3,K,A*10<CR><LR>
VTG - sentence type
GP - two code device for who sent the data (ex. CP = chart plotter)

Other baud rates are available -> High speed 38400

The exact message protocol for each sentence type is defined in the NMEA 0183 specification(s). I have come across a few nice individuals who have posted most of the sentences on the internet.

Cheers,
JMA

KU5D · Posted: Tue Apr 15, 2008 5:23 pm

www.google.com is a great thing. Search for NMEA0183.

http://www.kh-gps.de/nmea-faq.htm

Here's a link that should get you started. Keep in mind that some of the sentences from the receivers have redundant information, and most receivers do not by default send all the sentences described in this text. Your mileage may vary, but this is a good place to start.
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