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Monday, September 20, 2010

Arduino GPS - data logger added


I got the data logger shield from adafruit.  A nice kit
It was 19.50, which if you count the parts and proto board, i think it is a good deal.  It would have cost me more to buy separately and it looks professional and fits right on top of the Arduino.

The sdfat library i mentioned in an earlier post worked first try after i soldered up the board.  I was able to run their data logging example first try on an SD card.  Pop it in the computer and the file is there.  Totally awesome.

I pasted my gps code from the ebay SIRF3 tinygps library (in an earlier post) together with the sdfat data logger code.   I made it only record data when it had a GPS fix that was >0ms and <2000ms to filter out no signal cases that were filling the file with zeros.   A little messing with the header that gps visualizer wants on top the file.  and i was good to go.  Sitting at the kitchen table it logged data just fine.

Tossed on a small LCD 8x2 display i got off EBAY so i could tell what it was doing.  Between the SD card, GPS and LCD the pins are maxed out on the Arduino.

I used a USB cigarette lighter plug and a USB cable and took it in the car with me.  I drove on some errands.  The GPS showed all zeros, no signal.  boo!!!!!   Held it up through the sunroof.  Still NADA.  Frustration mounted.    Tried again the next day driving to work.  Nothing.  AAAAARRRGH.  Is the GPS signal that weak?

Brought it back inside, plugged the USB into my computer.  Bingo! signal!  Working great again.  Walked out to the car.. still working fine.  Sat in the car with the Arduino and GPS powered from the laptop USB on battery power.  Works great.  Here is a picture of my walk to the car, from gps visualizer.

So the problem was the power, either the current or the voltage supplied by the cheapo USB cigarette plug is too low for the GPS to get signal.  OK tomorrow we run with the 9V adapter and my inverter!  Banzai!

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