Deck the Halls with Raspberry Pi

I'm continually on the lookout for ways to connect with my children, especially my eldest whose natural interests seem to be rather different from mine. Going into parenthood I expected to engage my children easily over interesting science and technology subjects. It's certainly in their blood: their mother is a scientist and I am a software developer and general tinkerer. Reality has, as it so often does, proven less straightforward, more ambiguous. I'm sure there are many causes and influences, but one obvious theme concerns the sheer scope and pace of technological advancement since my own childhood. My first computer — a Commodore VIC-20 — seems hopelessly primitive next to the bewildering assortment of hypernetworked computing devices my children see their grandparents carry in a pocket.

While I struggle to identify the essential difference in our experiences, I suspect that part of what has changed is that my children aren't interested in computers as such the way I was. They beg to get tablet time to watch videos or play an online game, but everything they experience is professionally produced and logically ordered, with all the rough edges and sharp corners neatly rounded off into beautiful, pleasing curves.

My formative experiences were quite different. To them, using a VIC-20 would seem like a pathetically empty experience by contrast with the devices they're used to. No slick fade ins to carefully crafted notifications blending seamlessly with expensive, highly tuned interfaces to precisely-defined destinations. Even turning the VIC on felt like a primordial act, the massive, honest-to-goodness SPST coursing with power that flowed past your finger and off toward unknown and terrifying adventures. Yet even after that nothing much happened, nothing but a blinking blue expectancy, a half imagined whisper of potential. But of course that was the magic of it: you didn't turn on a VIC so much for what it could already do; you turned it on because of what you could make it do, for all of the wonderful creative possibilities its existence suggested. While the intervening decades have brought transformative advancements in the capabilities of our information technologies, the exploratory capacity, this frontier-like horizon that was the VIC's foremost asset, can become lost in the well-worn ruts of design.

This helps explain why, on a whim shortly before Christmas, I packed my boys into the truck and headed over to Micro Center to pick up a Raspberry Pi 2. The actual purchase jarred me a little by its contrast with my childhood memories, the agonized handwringing and haggling over the purchase of some part or accessory, which cost much more and did much less than the tiny little box the three of us carried out of the store. But there's something compelling about these little devices that manages to recapture some of the joy of possibility that hooked me on computing in the first place. Perhaps it's the physical board itself, so unlike a phone or tablet, with its rough circuit board edges crammed to bursting with connectors, sharp solder points and interface pins sticking weirdly out of every surface. Or maybe it's the surprising scale that delights, the wonder that something so small can do so much. It could be all those I/O pins practically begging to be hooked up to lights, sensors, and other gizmos. Whatever the reason, there is something about this device that manages to break through the conventional abstractions to reawaken wonder, the possibility of possibility.

Our first Pi project was a humble one: we hooked up a software-controlled LED, which is pretty much the equivalent of “hello, world!” for the Raspberry Pi.

As with most tech projects, even something as seemingly simple as a light on a switch requires daunting amounts of paraphernalia, patience, and time. For us, though, that was part of the fun: trucking around town on some fool idea of dad's, rummaging in obscure corners of the basement closet for resistors, LEDs, and bits of wire, the improbability of seeing the Pi driving an HDTV, fidgeting while the adults scratched their heads over some technical snag.

To get started on your own Pi adventure, you'll need a Raspberry Pi board [1], a micro SD card with the Raspbian OS installed [2], a micro USB power source (such as a phone charger), a screen with HDMI or composite video inputs and appropriate cabling, and a USB keyboard and mouse. (Whew!) Test booting the Pi up to make sure you have a working setup; there is nothing quite like the frustration of getting stuck for an hour and then discovering a bad cable.

For the LED mini project you'll need a few more parts: an LED, a current limiting resistor, some wire, and jumpers to attach to the Pi's GPIO pins. If you've got an old desktop computer lying around, you can scrounge the LED, wire, and jumpers from its indicator lights. And you should probably get yourself a breadboard and jumper wires for it, but for this simple circuit I was content to solder the components directly.

There are many excellent showcase and tutorial sites out there to spur project ideas and help you get going. We headed over to Gordon's Projects Single LED tutorial, which takes you through the steps of getting the LED connected; he does a nice job of breaking the narrative into digestible chunks and interspersing concept explanations to help orient beginners. (I still find the multiplicity of GPIO pin numbering and addressing schemes confusing, but I don't at all fault Gordon for that). Following his instructions we quickly had the LED wired up and connected to our Pi, which we then tested with the gpio utility, prepackaged with Raspbian Jessie, that can be used to communicate with the Pi's GPIO bus. From the console we ran these commands:

The pattern of these commands is gpio <subcommand> <pin> <value>, so the first command translates roughly to “set GPIO user pin 0 to output mode.” GPIO pins can be configured for input or output, depending on whether you are reading from a sensor or driving a motor or LED. Once the pin was configured, we used the second command to turn the LED on and the third to turn it off.

With that working, the obvious next step was to control the LED using Python. There are several Python libraries for interacting with GPIO; we used GPIO Zero, as documented in this tutorial by the Raspberry Pi Foundation. Here's the same sequence of commands as above, but this time using Python:

Instead of interacting directly with the bus, GPIO Zero provides a number of utility classes for dealing with commonly used devices; unsurprisingly the LED class is used to control an LED. The class encapsulates the fact that the LED is an output device and configures the pin to output mode for us when we instantiate it.

Why 17? That's the pin number according to the GPIO numbering scheme, which is equivalent to wiringPi user pin 0 (hence the 0 in the gpio commands above); both refer to physical pin 11 on the board. Ahem.

Pin numbers aside, our next challenge was to make the LED blink, which we accomplished with this simple Python script:

By this point I'd pretty much exhausted the boys' attention capacity, so we got out coloring supplies and drew some Christmas trees. Taking the LED we'd wired up and pushing it through the cardboard yielded a simple Raspberry Pi-powered Christmas display! Over the next few days I added three additional LEDs and some programming to expand the display:

So was this project successful in establishing a deeper interest in the workings of computing technology with my children? Time will tell, but one gain afforded by our little hack is that it has given us a platform to talk about how other things work. They have many small toys that use microcontrollers to control lights, drive motors, react to button presses, and play sounds and music; seeing the construction of this simple project has let me draw their attention to the basic workings of such devices via analogy to our Pi tree. At least in a small way I think they are beginning to understand that electronic devices are not magic and to see how we might build simple devices like the toys they're used to.

My next project? I'm working on building a Raspberry Pi-based geotagger for my Nikon DSLR; I'll be documenting the steps in a series of posts over the coming weeks, so stay tuned!

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Resources

• source code for our Christmas tree display
• Raspberry Pi Learning Resources from the Raspberry Pi Foundation
• GPIO Zero library documentation
• Gordon's Projects GPIO Examples
• Gadgetoid has a nice interactive pinout guide

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[1]	I recommend the Raspberry Pi 2 Model B, but the older models should work as well. Avoid the Raspberry Pi Zero when you're starting out: the Zero is incredibly cool and tiny, but it is less user-friendly than the other models as it lacks some of their connectivity conveniences.

[2]	There are serveral other OS options for the Pi, and you should obviously go play around with all of them. The examples in this post assume the presence of several supporting tools and libraries that are preloaded on Raspbian Jessie.