mega:bit

So, it was the summer of 2015 and details had been released about the amazing-sounding BBC micro:bit that was going to be given to all Year 7 students to encourage them to learn how to program. As a soon-to-be teacher of computing at a secondary school, this was a very exciting to me and, for no good reason, I set about making a large mock-up of the micro:bit on the school’s laser cutter:

My plan had been to add the LEDs and switches and connect it to my Raspberry Pi so that I could write some simple programs in Python that would display things on my scaled-up micro:bit. I didn’t really have any plans for it except that I thought it might be fun to make and could be useful in my classroom. Then, I got a message from David Whale saying something like: “how do you fancy making that work with a real micro:bit?”. David, if you don’t know, is an amazing STEM ambassador, uber-geek, the former technical editor of The MagPi magazine and co-author of the excellent Adventures in Minecraft. He’s also a huge micro:bit fan. Could I resist? No!

David was lucky enough to be one of the few people with one of the early micro:bits and we set about finding out how to drive the LEDs on my big model from the micro:bit he had. With a bit of digging and Googling, I managed to pull together enough details (thanks in no small part to the photo of the PCB design on this news story) to work out the wiring for the matrix and where I could tap the 5 LED matrix signals from the PCB to complement the 6 that were available on the edge connector. David came over with his precious micro:bit, we held some wires in place on the micro:bit PCB and… it didn’t work. I’d made some invalid assumptions but, by inverting some signals we got it working! David carefully soldered five wires to the micro:bit and, after numerous iterations of the design, we finally had a working “mega:bit” such as the one you can see being used rather enthusiastically at The Bett Show:

And here’s David with another when the micro:bit was used to open the London Stock Exchange:

So, the mega:bit worked and, with rather a lot of work, David and I managed to release about 10 into the wild. But we were thinking: wouldn’t it be great if teachers could make their own: it could be a useful teaching aid or, at least, an interesting DT project. The problem was: we didn’t think people would be too keen to solder wires onto their micro:bit and, besides, it was all a bit fiddly. After some thought, we came up with a rather wacky idea: an “optical” mega:bit that required no permanent electrical connection to the micro:bit. Instead, we’d use an array of 25 phototransistors to sit in front of the micro:bit’s LEDs to read the state of the LED display and send it to our big display made up of 10mm LEDs. The “opto” mega:bit now works after a long hiatus caused partly by being sidetracked to help make the monstrously big “giga:bit” which you might have seen on some of the BBC’s Live Lessons:

So, the question is: is this new mega:bit design of interest to anyone? Are there any teachers out there who would be interested in making their own and helping develop the design? It’s not as polished as the original all-electrical mega:bit but, with the second half of the summer term drawing near, it seemed sensible to publicise the project up and see if anyone takes the bait! The body of the mega:bit is made of two pieces of A4-sized Perspex and this is where there is most scope for experimentation: the earlier megabit had a nice see-through box on the rear to protect the circuit board.

As it stands, this is the electronics module that makes it all work: there are two custom PCBs that I’ve designed and you should be able to spot a Kitronik edge connector holding the micro:bit which is then held on top of the 25 phototransistors by a laser-cut Perspex harness:

IMG_20160524_222036096If you’re interested in giving it a go, then get in touch. If there’s enough interest then I may be able to put together some kits but, at the very least, I will be able to give you the design files and point you towards the relevant component suppliers. However, please note: this is in no way an “out of the box” project – at this stage it is for people who are willing to tinker and fiddle around a little bit should problems arise. That said, the mega:bit does seem to work quite nicely at the moment!

Over the course of the next few weeks, I’ll start posting details of how the mega:bit works, how to construct it and also the design files. If you don’t see what you need, please do nag me!

For those who are interested, this is the parts list:

  • 1 x A4 black Perspex sheet
  • 1 x A4 yellow Perspex sheet
  • 25 x 10mm red high-brightness LEDs (mine are from Kitronik)
  • 25 x visible spectrum phototransistors
  • 25 x 100 ohm resistors
  • 4 x 74HC540 inverting buffer ICs
  • 4 x commoned SIL resistor array (10K)
  • 1 x Kitronik edge connector for micro:bit
  • 1 x BBC micro:bit
  • 2 x large push buttons
  • 5 x 4mm terminal posts
  • DIL sockets, connecting wire, etc.
  • opto PCB
  • LED & buffer PCB
  • 1 x 26-way male connector (2×13 way)
  • 1 x 26-way female connector (2×13 way)
  • 1 x short M-F 26-way extension cable
  • various nuts and bolts
  • probably some other things that I’ve forgotten