[PSUBS-MAILIST] GPS integrated into software package

[Jon Wallace via Personal_Submersibles]

FYI, I received a GPS unit from Adafruit yesterday and was able to interface it into my Arduino-type microprocessor package seamlessly.  Like the ONWA model that Cliff tested, this one also outputs data in NMEA sentences over Serial interface.  It provides location, heading, speed, date, and time when on the surface.  Under water I will rely on my compass for general directional awareness.
https://www.adafruit.com/product/746
Current sensors are O2, CO2, Cabin Pressure, Cabin Temp, Cabin Humidity, 36 and 12 volt state of charge, HP-Air psi for ballast control, depth, water pressure, and water temperature.  The final major sensor to be integrated will be the CruzPro water depth transducer which outputs in NMEA sentences and should be as seamless as the GPS was.
For those interested in such things; performance of the graphics rendering software (Processing) has been less than I anticipated using Raspberry Pi 2 Model B.  On average I'm measuring an 8 hz data refresh rate, which is more than enough for basic life support sensors but can make things like the compass display look a little "choppy" when turning in a tight circle quickly.  The biggest performance buster is graphical rendering of the compass rose which requires a lot of  calculations and image manipulation to display correctly based upon the heading.  This can be alleviated somewhat by simplifying the Rose design and/or displaying a static image of a Rose and overlaying information on top of it, but I found there was a point of diminishing returns in taking this approach and 8hz was the best I could acheive.  Removing the compass rose rendering completely and simply displaying a text box with the heading increases display speed significantly to about 20 hz which easily handles any compass movement without a hint of choppiness.
Pi 2 B has 900mhz cpu and 1gb memory.  OS performance is showing 36% cpu utilization, 525gb memory free, and no swap usage.  So the hardware is handling things fine which builds confidence that the bottleneck is the graphical rendering by the  Processing graphical software.  The new Pi 4 is advertising native OpenGL so that may make a difference since Processing uses OpenGL.
In any event, since fast tight circles are not a selling point for PSUBS vessels the graphical performance is not likely to have a real world impact in field usage.

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