7. AlaMode Arduino GPS and SD Card

Here’s my update on getting GPS and SD card working on the AlaMode with the Raspberry Pi.

Be warned: the GPS (Fastrax UP501) that the board is designed for has been discontinued on Sparkfun and Adafruit - I managed to snag the last one from Sparkfun. I’m going to guess that it may be possible to substitute another GPS if you get the pins and voltages right or find another supplier.

To get the GPS working, I used the example code here. As noted by Kevin, the silkscreen for the GPS connections are reversed, thus RxD is really on the far right.

I was able to successfully run the example application and detect satellites and get a good position fix. I did have to move the unit close to the window, in which case it typically saw 2-6 satellites, usually averaging around 4.

With the TinyGPS library it worked pretty nicely – I ran it constantly for over two hours and it kept outputting good data.

TinyGPS will not output data if there is no fix: that had me confused thinking something wasn’t working right, so I wrote a simple serial-to-serial passthrough sketch and monitored the NEMA output from the GPS on the Pi via minicom. Once satisfied the problem was with signal quality, I moved the unit to the window and then it began working.

Notice also the micro SD card inserted. I was able to run the test utility and it was successfully able to detect an SDHC 8GB card and read the FAT32 file system (in 8.3 format, which appears to be a limitation of the library). I did have to tweak the CardInfo example that comes with Arduino IDE, changing to Serial.begin(115200) and const int chipSelect = 10;

I still haven’t soldered on the shield connectors – no need yet.

So far I’m pretty happy with the unit.

Next: Level shifter to allow setting parameters on the GPS unit (to bring the TxD from 5->3 volts) and then data logging.

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