BBC micro:bit – handle with care

Here’s the TL/DR version of this blogpost: if you are using the BBC micro:bit, especially with children, make sure they heed the advice on these panels in the middle of the back of the ‘Getting Started’ leaflet. In effect this means you can’t easily use the micro:bit buttons when it’s plugged in to a computer, as the natural way of holding it is to put a finger behind the A button to support it as you push:

Still interested? Here’s the background.

I’ve had 3 preview teacher micro:bits for a few months, and they all worked swimmingly… until I started using them with children. One unit got warm but still worked, another got incredibly hot (dangerously so) and failed. I sent it back to the BBC and got a replacement unit, which worked fine again – until I started using them with children. The new unit also started getting warm, but it still worked.

The BBC told me the chances of having multiple failures were ‘billions’ to one, so there must be an environmental factor. They sent me 5 more micro:bits to test in the same ICT room, on the same computers: HP Chromebooks. I spent about an hour testing them – and they were all perfectly fine. Must have been a fluke. A billion-to-one fluke.

Then I tried them out with my Year 5 computer club – and 2 of the new 5 micro:bits also now started getting warm. Not dangerously so, but noticeably warmer than normal.

Logically the only explanation for the mystery of the micro:bits was: children. I toyed with the idea of positing a new particle called a childon. Children must emit childons which have the effect of frying integrated circuits.

It turns out that my experience with the micro:bit is reproducable, and is, I am told, caused by 3 things happening at the same time:

  • The micro:bit must be plugged into a USB socket that can deliver enough current to charge a phone
  • The user must be touching the metal test pads on the back of the device
  • The user must cause an electrostatic charge to go into the device

Now this is a bit of a problem, because I think these 3 things will happen really quite often indeed. Firstly, most children test code, upload it, tweak it, upload it again. Combine that with the need for batteries, I think most micro:bits will be plugged into computers most of the time. Our HP Chromebooks are not unusual devices in schools, they have USB 3 sockets, and apparently these provide enough current to be a problem.

Secondly, it’s hard to avoid touching the test points on the back, especially as the ones in question are immediately behind the A button. It’s natural to hold it there as you push the button. Is it reasonable to expect children always to remember to hold them by the edges?

Thirdly, electrostatic shocks. My problems were in a room where I’d never noticed static shocks, but the floor is covered in carpet tiles, presumably nylon, so it’s a possibility. In my main ICT room I get shocks all the time, so when we use the class sets with Year 7 we will all have to keep earthing ourselves on something – not quite sure what. Do I need to run an earth to every desk?

I write all this with a heavy heart. I like the device, I love the microPython on it, I’ve written Python games for it, I’ve re-made the ‘happy plant‘ physical computing project, I’ve planned lessons for it.

But I fear that unless teachers and children read the leaflet carefully and heed the advice, an awful lot of micro:bits will fail, some may even get dangerously hot – though I should stress only 1 out of 9 initial units felt hot enough to burn, but a high proportion of the micro:bits I’ve actually allowed children to use run warmer than they should and draw more current than they should. I do wonder what would happen to the warm units if left plugged in for a long time – there is another warning panel about not leaving them unattended and unventilated on the back of the Getting Started leaflet. Where do I stand legally, as a teacher, if I give a child a micro:bit to take home and at home it causes an injury or fire?

The project is already beleaguered by insane delays – we were supposed to get them near the start of the academic year. That was 2015. We finally got our class sets for Year 7 last week, but because of upcoming exams and school trips, I now can’t use them until after half term in the Summer 2016 term. It’s a one-off giveaway, so the current Year 7s will only get a few weeks’ use out of them – and then we may struggle to use them in class. “Right Year 7! Only hold them by the edges! Earth yourself! Don’t use them when they are plugged in to the computer!” I may be an exceptionally poor teacher, but I find children do not always hear, understand and follow instructions in class. And the supplied USB leads are so short, usage will anyway be quite comical given our PC base units are built into the bottom of the desks.

It all just seems like a tragic mess, a wasted opportunity. I wish the BBC had been able to say “we messed up, let’s hold it over a year and you can hand them out next year’s Year 7s, or Year 8s if you already told them they were coming.”

Luckily I have still not told my current Year 7s about the micro:bit. And I am still not sure what to do with them.

How not to handle a micro:bit:

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8 Responses to BBC micro:bit – handle with care

  1. Richard Sewell says:

    Is that a job for a bit of gaffer tape, or some sticky -backed foam, to insulate the back ?

  2. Adam says:

    I was sure something like this would happen (either that or students spilling liquids on them when at home and shorting things out). I went the whole hog and designed an enveloping plastic/rubber case that exposes the buttons, connectors, and has a clear window for the LEDs. c.f. http://ittybittycase.co.uk

    I’m trying them at my school, and making them for other schools. They cost a few pounds to make, but if you email me, I’ll send you one to try out and see how it goes — I haven’t been brave enough to seriously destruction-test them yet (I don’t want to risk our school ones! Waiting until I can buy some online), so it would be good to know if they work out for you.

  3. Adam says:

    @Richard – there’s definitely issues with heat dissipation. In testing out different depths and form factors we had overheating problems with some of the components on the PCB until my colleague put a 1-2mm air gap all over the surface, and room at top for it to vent.

    So, tape might be fine, but … I’d want to be quite careful about checking what it’s covering :).

  4. David Evans says:

    I am an adult who bought one for myself to play about with. I have got a program working on it which I wrote in Python. It logs temperatures to a file. This has worked perfectly O.K. previously but now the whole board overheats and only works when connected via USB, not from batteries. In addition bluetooth has never worked.

    I am very disappointed; if I was a child I would be broke-hearted and would have given up programming then and there.

    The board does not seem suitable for the rough and tumble of a classroom. I know because I was a teacher for 25 years in Secondary Science.

    This needs a clear warning about shorting or static effects from the body or it should be sold with a case. If I had known this I would have immediately built a LEGO case.

    I think the BBC Microbit I have is finished and I am unlikely to get a replacement. Nevertheless I will move on to the real thing and get a Raspberry Pi.

    • blogmywiki says:

      Dear David – bad luck, sorry to hear that you’ve had the same sort of problem I had with my initial units. Have you tried getting a replacement?

      I have used them again in Year 8 classes last month and didn’t have any more failures, though we did find a dud lead which was causing us to think a micro:bit had died.

  5. Tom says:

    Ouch. I just found this by googling “Micro:bit burning”.

    I just plugged a relatively unused Micro:bit into USB for flashing, same as I have for two others. It’d worked a couple of minutes before when I pushed the MicroPython “firefly” code to it, and after flashing another board, I plugged this one back in. After a few seconds sensed a “hot” smell.

    As it hadn’t lit up yet, I guessed it was this board, so disconnected the USB quickly from the far end — plugged into my USB hub — and then picked it up to take a look. Bloody hot… now I have a small welt on my thumb, which really hurts!

    The board’s now dead for all intents and purposes. I’m fairly sure it was in the area of the smaller USB processor chip. I guess the voltage regulation that chip does for the rest of the board was a bit too much for it.

    I don’t work in education, but as with the Raspberry Pi — which can be so easily fried by a misplaced cable, or even just looking nastily at the SD card — I just can’t see how these things are meant to work in schools. I’ve got experience working with a fair range of microprocessor boards, and these ones do seem a little fragile, if you ask me.

  6. Gerry Murray says:

    Hi BlogMyWiki

    I was interested to find your overheating post here and it chimed with my own experience.

    I’m a STEM amabassador trying to work with some young people using the microbit.
    I’ve already fried one of them myself and had to replace it. I’m a bit miffed as I’m an Electronics Engineer and I’m *very* careful about static shock.
    However, one of the young people I work with has had 3 go faulty on him with the overheating issue. They’ve all been paid for by his parents who could well do without the extra expense.
    The whole microbit thing seems a real shame:
    Clunky programming tools.
    No inline debugger
    Flaky hardware
    We’re about 35 years after the BBC micro and the microbit seems to be a backward step.
    Very sad.
    Gerry

    • blogmywiki says:

      Hi Gerry – thank you for your comment, which chimes with my early experience. I had several go ‘pop’ in my junior school ICT room, only 1 die in the senior school ICT room. I did some work with what was the BBC micro:bit team and the thinking seemed to be it may be a conjunction of using the high current charging USB ports on our Chromebooks and touching the gold test pads on the back (hard to avoid even in normal use). Could the kind of USB port be a factor with your youngster?

      As for clunky programming tools, I mostly used Python in the Mu standalone editor and I found it a very good way of introducing textual programming languages to year 7/8. The simple block editor worked well with younger pupils also.

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