INTERFACING GPS and pcm/cia card

[kb]

I am using a John Deere starfire GPS system which samples at the rate of 1 Hz. I have a pcm/cia card that has a very high sampling rate. I need to know:
1. How to read the latitude, longitude and time from the gps through the serial port.
2. Also need to know if there are any prewritten vi's that can account for the difference in sampling rates. Kindly help.
Thanks,
Kb

[dhuff]

The John Deere Starfire GPS Receiver sends position data using the J1939 standard. This is a CAN protocol defined by SAE (Society of Automotive Engineers). The message you would need to read for the position is defined in the SAE documents, which can be bought from their website. http://www.sae.org

You can't wire the CAN bus directly to the serial port of your computer, you would need an adapter to translate the messages from the CAN bus to a port on your computer. If you have a CAN communications device, then it is just a matter of reading the message, and decoding it.

[waldemar.hersacher]

Hi Kb,
I don't know your receiver but the GPS systems I know use NMEA strings to output their information. To get them you need to send some commands to activate the output and type of string. Then you will get the strings one per second immedeatly after the change of the second. We have done this in C for a application running under MS-DOS so I do not have any VIs.
You should have some documentation about how to get it and how the strings are formatted.
If not contact me at buero@hersacher.de and I will extract the commands from the application.

For your second question what pcmcia card do you have? What want you do? Do you need subsampling the data to 1 Hz rate or what else?
Waldemar

[dhuff]

The answer above is the standard �official� answer, mainly because the receiver has many different versions, and the receiver was designed to communicate on tractors using CAN.
The fact is that the Starfire GPS does have a NMEA type of output, but it is very dependent on which model you have and what software is in it.
1. The receiver MUST have 12V on pin B and pin F, and ground on pin E
2. The serial data output is on pin G for new receivers (L band), and pin H for old ones (C band)
3. The port settings are 8 bits, 1 stop bit, 0 parity bits
4. The baud rate is configurable, but 4800 is the most common, some older units have different non-NMEA message format with 19.2K
5. The update rate and messages out are also configurable, so you may hook it u
p and see nothing out, because it is not configured right.
6. The messages supported vary with what software is loaded in it, but most have GGA, GSA, RMC, ZDA, VTG messages. Ask someone else who has the NMEA spec what those messages mean.
You can find many free NMEA readers out there, try using one of them to listen to the receiver. If you post your email address, I could send you better details and information.

[Khalid]

Hi,

I have to do something similar -- connect to a CAN network from a Serial port.  I am looking for recommendations on CAN-to-Serial converters.  And, as a bonus, any VIs / info' that can help me get started. 

Thank you!

-Khalid