The Ghost Controller – for Virtual Mazes…

Many years ago I coined the phrase ‘conceptual magpie’. Some people would argue that I’m not the first to think this way – depending on which online source you believe, either Dali or Picasso apparently said “Good artists copy, great artists steal.”

Like so many other teachers, I trawl forums, twitter feeds, blogs and books in search of that elusive holy grail – inspiration. The other day, I saw something that caught my imagination @joshburker embedded a video from and I knew I’d have to introduce the Robo-Sharks to this when we next met.

We’ve done outrageous user-interfaces before:

  • A Red Nose Day Joy Balloon
  • The Joy Can – a liquid-filled 3D tilt switch
  • Computer-Moderated Board Games
  • Bottle-top Buttons

Come to Scratch in Control – our free one day training course for teachers in Prague on Scratch Day, May 18 2013 – and you’ll see some of these (and much more) in action. But rather than use a Makey-Makey, I decided to do this one with a Picoboard – just for fun.


ghost maze controller
Here is the entire setup – the maze script running on the computer, the maze taped to the top of the ghost controller and a Picoboard peeking out from under it.

There are loads of ways we could have tackled this – one of the Robo-Sharks suggested we could have just taped a JoyCan to the bottom of the maze controller. That’s what I like to see – build on an existing solution. But not this time. I wanted something that would be reasonably easy for other teachers to replicate in class. And, as another student had already pointed out; letting kids loose with cans that are half-full of water in close proximity to computers is tempting fate a little…

So, just to be different, I decided to use four reed switches (they call them jazýčkový spínač – tongue switches – here in the Czech Republic). They switch on/off if they are in close proximity to a magnet. I taped each of them to the outside of a thin plastic container, and put a magnet – the type you use to attach things to fridge dooor and whieboards – to roll around inside it.

reed switches
Here is the underside of the controller, you can see the reed switched, taped to the plastic container, plus the magnet used to turn them on/off as the controller is tilted. The clips are connected to the Picoboard

This was then taped to the bottom of a spare thin card box I just happened to have lying around, and a copy of the maze I’d drawn in Scratch variant BYOB was taped onto the top. No expense spared here – Heath Robinson, Rube Goldberg, you aint seen nothing…

The most difficult part of the whole exercise was ensuring that a downwards left tilt corresponded to a left roll of the ball on the screen and so on…

It was fun, reasonably cheap (4 reed switches cost about the equivalent of US$4 here) – the components can be easily re-used/recycled and the coding can be as simple/difficult as you want.

To extend it – a classier endgame sequence would be a start, A timer, a score including penalties for hitting the edges. I’d favour an ‘augmented reality’ style of approach – taking a photo on the maze controller and perhaps shifting it slightly when the controller is tilted.

My students wanted to add monsters to avoid…

Personally, I’d go for a curriculum-related option instead. Navigate the maze to collect three numbers that add up to 100 or which are all factors of 108. Make your way to the exit while spelling out a key vocabulary term by rolling the ball over specific letters placed in strategic points in the maze.


Happy Earth Day

For Earth Day today, we looked at binary trees with my IB Computer Science class.

We’re studying abstract data structures, so last week we used BYOB to create stacks and queues with new blocks for all the associated methods you would normally expect with each structure.

The BYOB tutorials cover trees, so I decided to start with with a presentation using Google slides, and a simple scratch implementation, using a set of lists to store the data structure. It would be possible to use a single list to store this data, but that would be less straight-forwards for someone to change.

Scratch Project

Then we went on to do tree traversals…


Website Banners!

This week, I’ll be adding some banners to a few of my own websites to tell the visitors and users of some of my other resources about Scratch in Control.

Watch out for them. Here are a few examples:

Feel free to add them to your own website and link to here, the Indiegogo page or the Eventbrite page

A Shortcut and a QR Code

Ever since my students’ participation in BIMA D-Day, every time I’ve put together a site as an educational project that I’ll be presenting, I create a shortcut.

The shortcut may be smaller, – good for adding to microblog posts but often isn’t simpler.

However, the url shortener also creates a QR code. I joked with my class that adding this was to the blog pretty lame – why would someone reading the site need to see a QR code to get there.

Then the smartphones came out – a quick snap, and the blog was visible on their small screens

So, here’s the QR code for this site – I’ll be adding it to the ebooks and other resources too…

QR code for

Our Pitch Video


In case you’re wondering, yes the pitch video for our Indiegogo campaign was done entirely in Scratch! I’ve uploaded the source code to the Scratch website.

Some technical notes:

The background music was provided by Stellardrone,  a very generous musician who releases all his work under a form of Creative Commons style attribution license.

The cog was first drawn in Scratch and then converted to a sprite. However, you will notice that I should have kept the cog and its shadow separate in order to achieve a more convincing 3D effect when animating them.

The presentation timings are co-ordinated by using five different broadcasts to mark the transitions between the different phases.

The video was recorded using Camstudio – free screen capture software, and then tidied-up and converted to a smaller wmv file using Windows Live Movie Maker.