Nuts and Volts - May/June 2018

76 May/June 2018

Microcontrollers versus Single Board Computers

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

Computer

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.