Nuts and Volts - August 2013

PICAXE PRIMER

■ BY RON HACKETT

www.jrhackett.net

Have A Piece Of PICAXE Pi

Judging from the email response to my parting question last time, there's a fair amount of interest in exploring the possibilities of interfacing PICAXE processors with the Raspberry Pi (RPi), so this month that's exactly what we're going to do! It would probably take a couple dozen Primer articles to thoroughly discuss the various aspects of working with the RPi, but fortunately, there's a wealth of information available online, so there's no need for us to get into all those details here. Rather, I'll just suggest an online resource that I found to be especially helpful when I first started experimenting with the RPi, so you can begin your Pi explorations right away. (Of course, you may already have done that!)

Naturally, our first Pi-related project will be to construct a simple stripboard circuit that will allow us to easily access several of the Pi’s 17 GPIO pins. If you have already begun investigating the Pi on your own, you know that the GPIO pins are all 3.3V level digital pins. You have probably also read something about “level-shifting” and why it’s

14 August 2013

needed in order to safely interface the Pi with any 5V devices, including other microprocessors. However, we won’t get involved with that particular complication.

In keeping with the Raspberry Pi (and PICAXE) philosophy that “simple” is preferable to “complicated,” we’re just going to run both systems (Pi and PICAXE) at 3.3V. As you may remember, all M2- class PICAXE processors can operate with a supply voltage as low as 1.8V, so 3.3V will work well for our purposes.

Of course, we’re going to need a language to program the Pi side of things. When we get to that point (in the next installment of the Primer), I’ll explain why we’ll be using the Python programming language, and give some suggestions for getting started with Python, as well.

Before we begin this month, I want to thank the readers who took the time to respond to my question — I really do appreciate the feedback. In fact, I didn’t get a single “no” vote. That doesn’t mean, however, that there aren’t some readers out there who have no interest in exploring the Pi. If you include yourself in that group, don’t despair. Some of the material that we’ll be covering will also be applicable to non-Pi related PICAXE projects — especially the discussion of Python programming.

Why PICAXE Pi?

Here’s the very first question we need to address: “If the Raspberry Pi is such a powerful little computer, why do we need to interface it with a PICAXE processor in the first place?” The answer is simple: PICAXE processors have several hardware capabilities that are either missing entirely on the Pi, or are much more difficult to implement.