Using the 5Hz Locosys GPS with Arduino/ArduPilot

Sparkfun is now selling the excellent 5Hz Locosys (Mediatek chipset) GPS that Dean Goedde uses in ArduPilot. We're developing a daughterboard that will allow this 3.3v module to be a plug-and-play replacement for the 5v, 1Hz EM406 GPS that we're currently using for ArduPilot. In the meantime, if you want to start playing with a 5Hz GPS with Arduino here's some code and instructions to get you started.
The code is Jordi's new NMEA parser for the Locosys GPS. It's checksum verified, rocksolid, continuous, no delays, loop rate is about 32000hz. It uses pointers, so it's efficient.

You have to configure the Locosys for the first time you use it. It's very easy, you just need an FTDI cable. Be sure to connect the GPS to a 3.3 volt source. (We'll do this setup for you in the commercial version)

Instructions (please use the picture above as reference):

1-Run Realterminal and open the port @4800bps, you should see all the NMEA stuff, is not check the connections..
2-Now make sure you have checked the options marked with the green arrow... +CR +LF
3-Copy and paste this code: $PMTK251,38400*27 to the box indicated with the red arrow.
4-Then click the "Send ASCII" button indicated with the blue arrow..
5-Then the NMEA should disappear, and starting showing strange values. Go back to the "Port tab" (yellow arrow),
close the port, and choose the Baud "38400", and open the port again. You should the NMEA data again... =)
6- Then go back to the "Send" tab, and copy&paste this code: $PMTK314,0,1,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*28 then click Send, this should turn Off all sentences except GGA and RMC
7-Copy&paste now this code: $PMTK220,200*2C This should increase the updates to 5hz... (WOW!!!)..
8- Now you are able to connect the GPS module to Arduino, (only connect the RX pin to the TX of the GPS)
9-Then upload the code above, and open the port monitor, you should see Lat, Lon, Course, Speed, Altitude, Fix Position... like this:
46024504 8050998 312 0 519 1 (and yes you now know the exact position of my Swiss Chalet =P)...

If you want other setup codes for this GPS, you can find them in this datasheet.

Code explanation

If you'd like to understand the NMEA parser code a bit better, here are some of the library functions that it calls (all from the standard C++ library):

First of all pointers, which are very easy. They just give you the memory address where a variable is allocated in the ram: info
Then the strncmp(), better know as String Comparator. We use it to compare the header of the NMEA string "$GPGGA": info
Then strtl(), which means String to Long Variable. It converts a string number into a long variable: info
Then the strtok(). This is the string tokens, which looks for tokens in a string, for example commas ",", the ones used to separate values in the NMEA sentence: info
The atoi() will convert strings to integers: info
If you want to know all the available functions, see the library called "strings.h", "stdlib.h": info and info

(All these libraries are already installed in the Arduino IDE.)

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Comments

YOUSUF KHALIL YOUSUF February 4, 2010 at 5:17am

Is it possible to connect iPAQ GPS with ardupilot circuit or any type of GPS. Cuz I would like to use the ardupilot circuit for sailing boat application to control rudder i.e. to set the rudder in autopilot mode by using ardupilot.
I notice the ardupilot can only function by using GPS module like EM406 or 5HZ type..Please advise me if the ardupilot is capable to control it by using other type of GPS i.e. not a programmable GPS but with display unit like iPAQ or Raymarine GPS's...All the best..
Chris Brodeur February 3, 2010 at 5:32pm

@Dr Mike Black

I would love the link to the code...
Thanks
Chris Brodeur December 6, 2009 at 11:24am

hello...this is a great tutorial, it helped me get my LS20031 gps up and running.
The only thing i noticed though was that the link with the code for the arduino was broken...is this permanent?
RazorConcepts September 27, 2009 at 9:19pm

I need help getting this to work. I am using a Spakfun shifter board - com1. The GPS is running off a 3.3 regulator and I verified it is getting 3.3 volts. RX on the shifter going to TX on the gps, and vice-versa. Both realterm and hyperterminal at 4800bps and com1, nothing at all. realterm indicates a "break" at startup and then nothing afterwards. Any ideas?
ernani reis August 28, 2009 at 12:09pm

For the record: the $PMTK390, did work for me, no more nail bitting with the locosys status at boot. The command I used was: $PMTK390,0,5,9600,0,1,0,0,0,1,0,0,0,0,9600*3D'
Kyle Howen July 29, 2009 at 9:43pm

is the code for this unavailable now? It says access denied when i click on the link.
Mayur Topiwala June 30, 2009 at 1:04am

Hi all,
I've only just got this module and wired it up. My module's LED seems to stay 'ON' all the time. However, just by touching the unit or with a light/gentle tap, the module LED goes off and shortly after that it will capture. All seems to be well until power off, when once again, the LED will just stay on and I'd have to touch/tap the GPS module. I've double triple checked my soldering of wires etc. I'm not new to soldering.
Also, randomly, my settings seem to go back to default, ie, the GPS module defaults back to 5hz 57600 with all messages on.
Anyone else have this issue?

Looking forward to any feedback

Thanks
Alex H May 26, 2009 at 9:42pm

Answering my own question...

I emailed the manufacturer and got back from them...

"This is Eric Chin from LOCOSYS Technology Inc.

Thank you very much for this email and using our product.

All commercial GPS module has altitude limitation, 60000 feet. If the module over the altitude specification, it will not get position immediately. "
Alex H May 17, 2009 at 4:48pm

Anyone know if this GPS module has the 60k feet altitude lockout?

Thanks!
yogesh April 26, 2009 at 5:43am

Hi all,

Just an addition to what is being said here - We finally got the GPS coordinates from the LS 20031 after setting the baud rate as 57600 in Jordi's code as well as in the serial monitor window.

We directly connected the GPS module to arduino without configuring it using the FTDI cable. After playing around for a while, we found that the default baud rate of the module to be 57600bps, instead of the 9600 specified in the datasheet. Though we are not sure, the default update frequency seemed to be around 5Hz instead of the 1Hz specified in the datasheet.

We are also attaching a pic here of the GPS-Arduino connections. Hope people find this useful.

- aravind, yogesh

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