Novatel OEMV1 GPS Connection

[Ben]

I have a Novatel OEMV1 GPS board that I want to connect to my Gluonpilot board. The OEMV1 uses 3.3V power. It has a communications port that is LVTTL. The Gluon board is 5V. Would it be safe to connect the two (as far as I know it would be)? I am planning to connect only the Gnd, Tx and Rx.

The Gluon and OEMV1 boards are currently powered by different batteries. I need 5.5-16V to power the active GPS antenna, so I’m using a 12V battery to supply power to the active antenna and a DC to DC converter to supply 3.3V for the GPS board. In the near future I plan to add a second DC to DC converter to supply 5V for the Gluon board.

I can control the OEMV1 board via software. I can set it to a chosen baudrate and I can tell it to provide RMC and GGA (I think these are the only two signals used by the Gluon board). I have no experience with NMEA, but I notice that the LS20031 documentation talks about MTK NMEA packets and starts messages with $PMTK while the Novatel documentation says that the messages start with (e.g.) $GPGGA and $GPRMC. Will the Gluon board handle this? Note also that my OEMV1 board is currently only running at a 1Hz rate, but could be upgraded to 10Hz. As soon as I hear back on the electrical connections I can give it a try. Any ideas about the best procedure or sequence to try?

Ben

[Tom]

Hi Ben,

This should work. Your GPS will output RMC and GGA which the gluon will interprete.
The start up sequence for the GPS unit is:

- Open serial connection to GPS with the baudrate specified
- Wait for data (+ timeout)
- Change the update rate & select correct NMEA sentences using MTK-specific commands
- Change the GPS baudrate to 115200 using MTK specific commands
- Change serial connection to 115200 baud

If you make sure your GPS only outputs RMC and GGA, and the start-up baudrate is 115200, the connection will work. You might get some errors during start-up, but these will time-out and everything should work fine. (look in the gluon config for the status)

Code is here: http://code.google.com/p/gluonpilot/sou ... s/gps.c#54

Tom

[elkaim]

Hi Tom and Mitch,

I am still having some issues getting my GPS to be recognized. I'm using one of the uBlox 5 receivers with the sarantel antenna, from DIYDrones. Looking over at Ben's message, on the other GPS, I will try to set the uBlox for 115200 and only GGA and RMC messages.

I'll see if that works.

--G

[elkaim]

Well, that did not work.

I can't get the NMEA output to go faster than 9600 Baud. I'm checking the message protocol and I think that there is a compatability thing going on, originally NMEA was limited to 9600 Baud. After playing with this quite a bit, I have to choose between NMEA at 9600, or Binary at faster.

I'm trying to modify the software, but I can't get it to compile (missing a common.h file). Tom, this was not in the SVN, so I was hoping to be able to modify code here.

Any suggestions?

Thanks, G.

[Tom]

Hi Gabriel,

Yes I forgot to check in common.h a while ago, but it is checked in since r39.
Be careful: the latest code revision (r40 and +) is still experimental and has a lot of changes.

You really need a gps faster than 9600 baud, otherwise you are limited to 1 Hz NMEA. The gluonpilot changes the baudrate and selects messages with MTK-chipsets only commands.
If you are having a lot of issues, I'd suggest buying a new GPS module, they are becoming really cheap (<50$). Sometimes you need to face the fact that your own free time is very precious as well

I might one day implement the ublox binairy protocol, but priorities are different for the moment.

[elkaim]

Hmmm,

Looking at the terminal out of my program, NMEA at 9600 with just GGA and RMC messages seems to be OK at 4Hz. I suppose that I could write the binary parser, but I would rather spend my time doing other things right now.

Quick question, how do I get the previous version using the SVN trunk (I'd still like to modify the code a bit).

--G

[Tom]

Then you would need "r39". It depends on the SVN tool you use how to get it.

If you want to use the GPS at 9600 baud instead of the 115200 operational baud, you need to modify this line:
http://code.google.com/p/gluonpilot/sou ... /gps.c#110
OR
http://code.google.com/p/gluonpilot/sou ... s/gps.c#93 in case the module times-out when looking for the GPS module

If your GPS is correctly configured on boot-up you could even delete all the previous lines and only keep

Code: Select all

uart2_open(9600l);
IFS1bits.U2RXIF = 0;    // Clear the Recieve Interrupt Flag
IEC1bits.U2RXIE = 1;


in the gps_init() code

Tom