Ultimate GPS Breakout - minor issue at high altitudes

[rbergerpa]

Hack Pittsburgh did it's "C1" balloon launch on 11/11/12. The balloon carried an Adafruit Ultimate GPS Breakout Board using it's on-module logging feature.

It mostly worked well, but we discovered a minor glitch: at altitudes above 32,767 meters the recorded altitudes wrap around to negative numbers. By comparing the altitudes with the trend before and after the negative numbers, it appears the GPS calculated the altitude correctly, but the wraparound occurred when storing the value in the flash as a 16 bit signed number.

If we correct the negative numbers by adding 65536 we get values that make sense relative to the surrounding numbers.

Using this technique, we logged a max altitude of 34046 meters ( 111,757 feet )

Other Adafruit products were used on the launch and worked well:

Weatherproof 18B20 temperature sensor

Two Adafruit Data Logging Shields

Serail JPEG Camera (watch the Hack Pittsburgh site; we will add the pictures soon)

Robert Berger
Hack Pittsburgh member

[adafruit]

is the bug in our parser or the NMEA output?

[WethaGuy]

32,767...65,536. This has to be a valued stored as int when it should be unsigned int. It would more correct to make it a long, since it's technically possible to have a negative altitude (below sea level).

[buprafisc]

Hello,
Sorry for my bad english but I'm French.
Could you tell me if Ultimate Gps Breakout is comptatible with Arduino Due ?

Thanks.

Thierry

[adafruit_support_bill]

Yes. It will work with any 3.3v or 5v microprocessor.

[buprafisc]

Thanks

Thierry

[rbergerpa]

is the bug in our parser or the NMEA output?

I wasn't using the NMEA/serial output; the bug occurred when using the "log to internal flash" feature of the module, and then extracting the data with the MT3339 GPS PC Tool

[adafruit]

oh, yeah the internal logging stuff is hardcoded - it was not designed for use at high altitudes!