76 May/June 2018
Microcontrollers versus Single Board
Microcontrollers like the PICAXE are so easy to use.
Partly because they’re single-task programmable logic
integrated circuits with a built-in command set that’s
capable of making the PICAXE read GPS sentences,
digitize voltages, operate servos, trigger events, store
data into EEPROM, and more. For students exploring
programming for the first time, their programming language
(BASIC) represents a very shallow learning curve. For this
reason, I argue that microcontrollers like the PICAXE make
the best avionics for a first time BalloonSat program in the
junior and senior high school setting.
The Raspberry Pi, on the other hand, is a single board
computer. It’s reminiscent of the first home computers that
became popular in the late 1970s and 1980s. One reason
for this similarity is that the Pi must boot up and load
its operating system (OS) into memory before it can do
anything else (this is very unlike a microcontroller).
Another reason for the similarity is that the Pi is
designed to be programmed by the user rather than for
running programs and apps already written by other
people (remember the Timex-Sinclair 1000?).
Because it has an OS, the RaspPi is not a real time
device. While the PICAXE will perform a single task exactly
the same way every time (according to your code), the
Pi does a lot of additional stuff in the background while
carrying out the program it’s running. With its ongoing
background tasks, there’s no guarantee that programs will
finish in the same amount of time every time.
Having an OS also means there’s a lot of code to
load and memory to check when a Pi boots up. Then,
after booting up, the Pi waits for input on what action
Raspberry Pi Zero Flight
n BY L. PAUL VERHAGE NEAR SPACE
People write a lot about the Raspberry Pi single board computer (SBC) and the Arduino microcontrollers. I’m a BASIC Stamp and PICAXE man myself, but thought it might be fun to expand out a little bit after all that I’ve
read. So, over several columns, I’d like to share my exploration of the RaspPi
as a flight computer for BalloonSat missions. I gotta tell you, this has been a
real experience for me.
On the left is a small Raspberry Pi Zero. I’ve connected it to the expansion
board that I designed to create a RaspPi BalloonSat flight computer.