GPS Nema sentence

Information about using GPS units with motec devices

GPS Nema sentence

Postby Hugh on Mon Jan 30, 2012 5:49 am

I am trying to build a GPS + acceleormeter + gyro system to feed accurate speed for launch control and position info for track mapping into my ECU & ADL.

Can anyone advise what the output word looks like to feed into the RS 232 port on the MXXX ECU's?

I have seen a note from Holms that the word contains is in a standard NEMA format.

From the Webinair, it seems that the following information is available for logging, so the word must contain at least this information:-

Time HW
Time LW
Latitude HW
Latitude LW
GPS Londitude HW
GPS Longditude LW
GPS Speed
GPS Quality
GPS Sats used
GPS HDDP
GPS Altitude

If someone has an example of the exact format, I would be very grateful.

Thanks

Hugh
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Re: GPS Nema sentence

Postby Holmz on Tue Jan 31, 2012 10:53 am

My windows drive died - so when I get that refigured out I will post it.
(For my future use as well) 8-)

Otherwise I am pretty sure that it was Darren Reynolds that sorted me out in the past.

I am not sure if you can do the maths in the ECU to know a more accurate speed. So you may need to do that in a separate unit (Blackfin etc). The other option would be a GPS-Aided AHRS (Attitude Heading Reference System) that computes the speed and outputs that.
http://www.xsens.com/en/general/mti-g or http://www.microstrain.com/inertial/3dm-gx3-45 - and get MoTeC to do the template and comms for you.
If you have wheel speed sensors, and not 4wdr, it is probably easier that way.
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Re: GPS Nema sentence

Postby Hugh on Sun Feb 19, 2012 3:30 am

Holmz,

Thanks for the links.

The device I am working with has 3 acceleromters + 3 gyros + GPS and will output real time speed to work with my launch control.

My car is 4WD and spins all four wheels on launch, so need the independant speed input to make the launch control work.

I will do all the maths in the unit I am working with, just need to know the best way to feed the information into the ADL or ECU.

I found this link www8.garmin.com/manuals/GPS18x_TechnicalSpecifications.pdf to the Garmin GPS.

There are quite a few references to NMEA 0183 sentences which is what I assume I need to output.

From Page 16 in the Garmin document it describes the content of each sentence.

The sentences have names like GPSA and GPVTG, there are quite a few different ones.

Do you know which sentences Motec will read?

Thanks

Hugh
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Re: GPS Nema sentence

Postby Holmz on Sun Feb 19, 2012 12:02 pm

Hugh wrote:Holmz,

Thanks for the links.

The device I am working with has 3 acceleromters + 3 gyros + GPS and will output real time speed to work with my launch control.

My car is 4WD and spins all four wheels on launch, so need the independant speed input to make the launch control work.

I will do all the maths in the unit I am working with, just need to know the best way to feed the information into the ADL or ECU.

I found this link www8.garmin.com/manuals/GPS18x_TechnicalSpecifications.pdf to the Garmin GPS.

There are quite a few references to NMEA 0183 sentences which is what I assume I need to output.

From Page 16 in the Garmin document it describes the content of each sentence.

The sentences have names like GPSA and GPVTG, there are quite a few different ones.

Do you know which sentences Motec will read?

Thanks

Hugh


Which device is it?
You either need to come in through the RS232, or through a CAN address.
If go CAN then you can get it into the ADL and probably the ECU (I know Lambda can go in as CAN), but you will need to check to see whether it needs to be RS232 into the ECU for TC.

If you are in Au - then contact MoTeC in Croyden South and maybe they can do a template for you.
If you are in the US then Huntington Beach.
If Eu there is a HQ over in that area.
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Re: GPS Nema sentence

Postby chelspeed on Sun Feb 19, 2012 7:39 pm

The GPS I have (the old motec us professional one) sends data from the GGA and RMC lists. Details of all available data in the NMEA GGA and RMC lists here:

http://aprs.gids.nl/nmea/

As an example some details here of how to add GPS fix from the GGA list:

viewtopic.php?f=26&t=89&p=1073#p1073

You can use the standard RMC GGA template in dash manager to get any of the above data from the two lists.
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Re: GPS Nema sentence

Postby Hugh on Mon Feb 20, 2012 2:06 am

Holmz,

The device I have is not yet available for sale.

I would like to stick with RS232 since that is more doable for me, but CAN will be an option later.
I am in the UK, so will give them a shout to confirm and see what they say.

Chelspeed, thanks for that, I can see that the RMC word has a speed component, I will try and get this word out at 40Hz on RS232.

The VBW and VTG word is the shortest, so might have been best, but RMC will be good if there is enough time to get it out.

Thanks

Hugh
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Re: GPS Nema sentence

Postby Holmz on Mon Feb 20, 2012 9:55 am

Nice!

The STC (Serial to CAN) can be used to put it on the CAN bus after you get the RS232 working.
You may want the output to be more like ~100Hz or greater at that point depending on what you are doing.
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