92 September/October 2018
APPROACHING THE FINAL FRONTIER
The one surprise I discovered while testing my code
is that the servo is jittery. This jitter makes me suspect that
the Raspberry Pi isn’t constantly applying a 50 Hz signal to
the servo. It may be that the Pi has to take turns performing
other tasks in addition to the 50 Hz signal generation. If
true, then when the Pi switches between tasks, the servo
signal drops out briefly creating the jitter I observe. If I can’t
find a way to remove the jitter, then I’ll instruct the Pi to
turn off the servo signal while the camera records an image.
After some hair pulling, I finally have the Raspberry
Pi-based near space flight computer recording both sensor
data and pictures on its SD card. Figure 5 is a screenshot
showing the contents on the Pi’s SD card after a practice
It’s been a real challenge getting to this point. As I
said last time, the Raspberry Pi and PICAXE work a lot
differently from each other. This has frustrated me at times
because of things like library importing and configuration
issues that the PICAXE doesn’t require. However, I guess
this goes with the territory with learning how to use a
general (and more capable) microcomputer.
Onwards and Upwards,
Your Near Space Guide NV
Wouldn’t you know it. I ran out of filament after printing most of my camera
rotator. So, you really don’t have to print it in two colors
like I did (in fact, I’d recommend printing it in black so
sunlight will keep the camera electronics warmer).
A folder and the contents of a file are shown on this monitor. On the left is the open file with the GPS, weather station, and Geiger counter data. On the right is the folder of the image files recorded by the camera. All I need to do now is
insert a thumb drive into the Pi and copy all the files on to its SD card. I now know how to get the flight data from the Pi to
my PC for further analysis.