Introduction: Arduino GPS Datalogger

Do you want to log some GPS data onto an SD card using your Arduino? Do you already own a Sparkfun microSD shield and GPS module? Did you try the Adafruit Sheild (although it is awesome and cheap) but it stole all of your pins? Want it to output into a nice, Google Earth friendly format? Well read on...

Step 1: The Hardware

You will need:
1. An Arduino (which ever you prefer. I stick to the uno, duemilanove, mega, and this bad boy )
2. A GPS module (I'm using the EM-406 from Sparkfun )
3. A matching way to hook the GPS module to the Arduino (I went with Sparkfun's GPS Shield )
4. And a microSD Sheild (Again from Sparkfun )

Some optional stuff:
5. Indicator LED (ok ok I won't force Sparkfun on you for this guy)
6. A nice hard weatherproof case (I used the Pelican 1010 which fit perfectly)
7. Battery (No point logging GPS data tethered to your computer)

Step 2: Hook It All Up

It's a simple as, stacking the sheilds.
I put the GPS Shield on top to maximize reception.
The led is on pin 13 (see close up pic). This will flash every time it logs a GPS point.

To work with my code, make sure the little switch is set to "DLINE" on the GPS Shield. (Included a close up if you have no idea what I'm talking about) This is so we can use pins 2 and 3 to communicate with the GPS instead of the "UART" setting, which uses pins 0 and 1. This is a personal preference, modify the code as you wish. If you are using the UART, then make to switch it over to DLINE while uploading code to the Arduino if the shield is attached.

Lastly remember to have your microSD card formatted to FAT (FAT16).

Sparkfun (and many others!) has some awesome tutorials on the product pages that I referenced in this Instructable's Hardware page for both of the shields. I'd highly recommend a glance through them if this is a little too confusing. (Especially the microSD tutorial!!!!!)

Step 3: The Software

I'm assuming if you've read this far you know a bit about the Arduino and how to upload programs using the Arduino IDE, so I will not be covering the basics. Lets walk through some sudo-code

initialize serial, libraries and variables.
create a text file on SD card with header
pull GPS data
write GPS data in the end of the text file.
flash led
keep looping

I'm not going to go into my code in to much detail but it's commented enough to understand whats happening.
You will notice I'm using two really awesome libraries written by Mikal Hart, so make sure you have downloaded them! (TinyGPS and NewSoftSerial )
TinyGPS basically makes it easier for us to extract data like longitude and latitude from the slightly complex NMEA sentences that the GPS module spits out.
NewSoftSerial allows us to transform any pins into "serial pins". In this case pins 2 and 3 as previously mentioned.

The Arduino file is attached.
Just upload and it should work! (Leave a comment with the issue if it's not)

Step 4: Great We Are Logging... Now What?

So as of now, you are logging all of the gps data onto a text file named trip.txt in the root of your sd card. If you disconnect power, then reconnect, it will just append the new data to the end of that file.
You are more than welcome to write some code that reads the SD card and says: "if the file exist, make a new one with a different name." You could even get creative and use the date and time from the GPS in the filename.
The possibilities are endless. I'm just doing some basics as a proof of concept.

So it outputs a text file with a heading and the data that looks something like this:

Now you can use an awesome tool over at to create a Google Earth File with the points and their data at each.
Change the settings to your liking and use upload or copy paste.
Its as simple as that.
The picture is an output from the data above.

Step 5: The Side Note

This is my first Instructable so please play nice.
This is simply a start in the right direction for a full on data logger.
In no way did I optimize my code or hardware to be as efficient as possible.
It doesn't take things like file size or bad gps data into account.
Unplugging the power could even corrupt the SD card. Easily fixed with a button and some start-stop code.

It simply says, "if there is a gps module attached, I will log whatever it gives me"

And that's it! Feel free to ask questions and I'll do my best to answer them and have fun!!!!
Post your projects in the comments if you use this, I'd love to see what you guys are doing!

-----------------------------UPDATE 10/10/12-----------------------------
Hey guys, I'm sorry to say, this project has been discontinued for now. It has been almost a year since I published this. I haven't had much time to update and fix the bugs in the code, however it should still be compatible with older versions of the Arduino IDE and libraries. Next project that I use the sd shield for I will come back and give this another update, but for now work and school are cutting into my project time.
Thanks for your support!

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