Connecting non-3DR GPS

Posted by Joe Dvorak on October 3, 2014 at 1:42pm

I have a Pixhawk system with all the standard 3DR peripherals (telemetry radio, GPS). I need to replace the 3DR GPS with another GPS unit so that I can conduct some tests with higher accuracy. I have a Trimble RTK unit and others at work that I want to try. I have no problem setting these up for the desired output so that is not a concern. I really just need to understand the Pixhawk/APM:Rover side better.

I've tried to find information about the configuration of the GPS port, but it is very sparse. Everything seems to try to push the 3DR modules (which I already have so I'm not cutting into their profits). The most information I have found has been on the Pixhawk webpage (https://pixhawk.org/modules/pixhawk) which let me know that the port is 3.3 V. But, there is no other information. I know it is possible to use other GPS systems. I can see discussion on the developer board about support for NMEA strings and custom RTK GPS modules.

Specifically, I'd like to know:

1. What protocol is used for the GPS TX/RX lines?

2. If it is UART, what baud rate is expected? If baud is configurable, where is it configured?

3. Do I need to change an APM:Rover parameter? I have found GPStype in the list, but NMEA is the only one I readily know how to setup. Are the others special for certain parts or are any generic protocols that I just didn't recognize?

4. What NMEA strings can it interpret and how fast can it handle them?

Thanks for any help anyone can provide.

You need to be a member of diydrones to add comments!

Join diydrones

Tags: apm:rover, gps
Email me when people reply –
Follow

Replies

    • Matthew Reimer > Hiroshi Fujii June 15, 2015 at 1:27pm
      There is a parameter called gps type that you can change. It should work on auto (1) but you could try changing it to serial (5) also note that gps type1 is on the gps port and gps type2 is on the serial port. There are some baud rates that don't work. I know that 57600 works.
  • Developer
    Andrew Tridgell October 4, 2014 at 3:11pm

    you might also like to try connecting two GPS modules, and set GPS_TYPE2 to 1 to enable the 2nd GPS. Make one a 3DR GPS and the 2nd the trimble. That will allow you to directly compare them. It will also mean you keep lock if the trimble acts up.

    • Joe Dvorak > Andrew Tridgell October 6, 2014 at 6:44am

      Thanks for the suggestion. I hadn't considered that yet, but it would let me run both without having to rewire everything every time I wanted to try something different with them.

      Joe

    • Nakia Brewer > Joe Dvorak January 8, 2015 at 2:02pm

      Hi All,

      Very new here, first post infact.

      I too am about to experiment with some RTK Trimble GPS through the Pixhawk. Joe, did you end up getting it to work after completing the level shifting?

      Is there any estimate of timeline for when the mission planning software will support mission items with better accuracy of 1m?

      Many Thanks

      Kia

    • Joe Dvorak > Nakia Brewer January 9, 2015 at 6:01am

      Kia,

      It did work once I used a level shifter. I used the Pololu 2301a Serial Adapter as I could get it fully assembled. I just had to make a jumper from the Pixhawk's connector to standard headers which made it easy to implement. The RTK GPS was setup to transmit NMEA strings on its serial port. I just had to connect it. As Andrew said, the Pixhawk recognized it without any problems and I could see it in mission planner. I haven't used the RTK GPS for navigation as my test vehicles are too small to reliably drive with the size of the GPS unit I was testing. Once I confirmed that the Pixhawk worked with the RTK GPS, I've been delaying further testing with it until the large vehicle frame is complete.

      Good luck in your efforts.

      Joe Dvorak

    • Nakia Brewer > Joe Dvorak January 15, 2015 at 7:32pm

      Hi Joe,

      Just an update to let you know I have progresses a little further.

      It appears the Trimble GPS I have currently doesn't support the GPS RMC Sentence Type so I am awaiting feedback from Trimble on what/if anything could be done from the GPS Side.

      Noting that I have another Trimble GPS at my disposal which does support GPS RMC so I am back on the testing path. Hopefully the 2301a will show up today so I may be able to complete some tests on the weekend.

      I would appreciate any pics or advice on how exactly you connected the 2301a between the Pixhawk and the GPS.

      Cheers

      Kia

    • Joe Dvorak > Nakia Brewer June 11, 2015 at 6:03am

      Nakia,

      Sorry for dropping off the face of the earth. We had snow storms and then the beginning of the semester that kept me from checking for a week or two and then I lost the messages.

      I setup the Trimble to export standard GGA. It worked great in limited testing. We have used several different Trimble units. The initial testing was with a 5800.

    • jean-luc > Nakia Brewer April 9, 2015 at 7:18am

      Hi Nakia,

      Do you have any news regarding your Trimble test?

      Regards,

    • jean-luc > jean-luc April 23, 2015 at 2:49am

      Hi there,

      I want to connect a other GPS than the 3DR and i make somes test with a C-nav and a Garmin GPS but no result for the moment...

      I'm using a MAX 3232 board between the GPS and the pixhawk to convert the GPS rs232 signal (-7/+7V) on TTL signal (0/5V).

      Configure the GPS to send NMEA-0185 sentences (GGA, VTG and RMC).

      Testing the system on a arduino uno, i can read the trame, all is ok.

      Put the system on pixhawk serial port 3 or/and 4.

      Using the 5vcc serial port pin to power my 3232 board.

      Select GPS1 and/or 2 type to NMEA .

      Configure the port setting (speed 19200, mode 5) and nothing comming.

      Test with all type GPS1 and/or 2, nothing.

      Test with only GGA trame, nothing.

      Invert rx/tx pin, nothing.

      I don't now where is the problem, i'm not testing to power the 3232 board on 3.3v for the moment, because i see that the pixhawk serial port are 5v tolerant.

      So, regarding the NMEA sentences, we need to have this three sentences on the signal or need only the GGA sentence for exemple?

      Someone have an idea or a concret exemple of working connection???

      Cheers

      Jluc

    • Georacer > jean-luc July 20, 2015 at 6:27am

      Jean-luc,

      You mention that you need to set the GPS output protocol to NMEA 0185. I mostly find references to 0183 and none for 0185.

      Did you do a typo?

      Is there an actual difference between them?

      Does APM accept either one or only one of those NMEA versions?

      Thanks

This reply was deleted.