Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Questions and discussion about running MicroPython on a micro:bit board.
Target audience: MicroPython users with a micro:bit.
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PixelShady
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Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by PixelShady » Sat Oct 26, 2019 1:47 pm

TLDR:
  • was yesterday
  • playing around with my first sg90 micro-servos
  • decided to start using an external 6V battery to power servo, to 'protect' my microbit from damage
  • was moving servo around while it was running
  • 6V-positive croc-clip touches the signal/control croc-clip for less than a second
  • POOF
  • smell of smoke and a tiny, shiny pimple of plastic on the main processor chip
  • 18 Euros (including postage) down the toilet
  • an expensive lesson

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pythoncoder
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Croc clips :-(

Post by pythoncoder » Sun Oct 27, 2019 7:33 am

In my first job after graduating the lab had a total ban on croc clips because of the trail of destruction they had caused. I never use them on anything smaller than a car battery.
Peter Hinch

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Roberthh
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Re: Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by Roberthh » Sun Oct 27, 2019 8:15 am

I never use them on anything smaller than a car battery.
Well, there should be some on the oscilloscope probe GND clip.

stijn
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Re: Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by stijn » Sun Oct 27, 2019 9:45 am

Good point, don't think I've ever seen a probe without it. Wonder why, could be because of historical/utility reasons; I find the signal end of a probe a better kind of clamp (though it cannot do everything a croc can).

To the OP: it's not unlikely the majority, from dabbling to fulltime working in electronics, is going to have a problem like yours at one point or another, it's hard to avoid when fiddling with loose wires etc. The upside however is that you usually learn from mistakes, and the chances that it will happen again should be a lot smaller now already since you'll be paying more attention.

When I just started I fried a 500$ dev kit in a similar way, was my employer's not mine but still from that point on I became much more careful with loose wires and make sure a clamp is always properly clamped even when not strictly needed. And some time later I kinda fried my hand after holding a naked power supply PCB which was disconnected from mains but with the capcitors still charged, and my palm touched both pins of the fat main capacitor. Apart from the burning marks and a ton of adrenaline my entire arm felt really funny and when pulling away from the supply I apparently also smashed my hand into a metal shelve for extra bruising. Well, that never happened again. Even now, years later, when I'm in the proximity of something of which I know it holds a serious amount of energy, my brain still goes like 'RUN!'. Again, learned me to be more careful.

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jimmo
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Re: Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by jimmo » Sun Oct 27, 2019 11:22 pm

stijn wrote:
Sun Oct 27, 2019 9:45 am
Good point, don't think I've ever seen a probe without it. Wonder why, could be because of historical/utility reasons; I find the signal end of a probe a better kind of clamp (though it cannot do everything a croc can).
They're usually removable, for high speed stuff you'll see a spring ground pin instead of the croc clip to minimise loop area.
https://i.stack.imgur.com/1yCGX.jpg

To the OP: Yep we've all been there! Sorry about your micro:bit :(

But as a sort of counter point (with apologies to the OP): I'm amazed at just how bulletproof the micro:bits are. I've probably seen close to 1000 micro:bits (a milli:bit?) go through some fairly heavy usage without a single failure. Admittedly we don't give the students access to any higher voltages than 5V...

My only wish was that the micro:bit had a LDO on the JST lipo input. And it would be great if it had some pin headers or a connector or any way of connecting stuff to it that didn't involve the edge connector. I'm a big fan of the Grove ecosystem from Seeed, so things like https://www.seeedstudio.com/Grove-Shiel ... -2947.html are really great, and they have Grove->Servo cables.

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pythoncoder
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Re: Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by pythoncoder » Mon Oct 28, 2019 1:45 pm

Roberthh wrote:
Sun Oct 27, 2019 8:15 am
Well, there should be some on the oscilloscope probe GND clip.
Well spotted. I don't think anyone pointed that out to the manager who banned them.
Peter Hinch

PixelShady
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Re: Anyone here want to share their stories about the first time they fried a micro:bit? - I'll share mine first.

Post by PixelShady » Mon Oct 28, 2019 3:03 pm

Thanks all for your responses.
jimmo wrote:
Sun Oct 27, 2019 11:22 pm
To the OP: Yep we've all been there! Sorry about your micro:bit :(

But as a sort of counter point (with apologies to the OP): I'm amazed at just how bulletproof the micro:bits are. I've probably seen close to 1000 micro:bits (a milli:bit?) go through some fairly heavy usage without a single failure. Admittedly we don't give the students access to any higher voltages than 5V...
I'm sure they are very tough, but only, as you suggest, using the built-in 3V output of the micro:bit itself; max output of which is only @ 100mA, I believe. I'm not going to try it, but I reckon even a single AA battery would be enough to fry a micro:bit the way I did it. A fully charged AA can output anywhere between 5 and 10 Amps when short-circuited, 50 to 100 times more than the micro:bit is probably designed to handle.

My recommended improvement would be a 0.1A SMD Resettable Fuse PPTC PolySwitch Self-Recovery Fuse fitted to most of the pins, a row of them above the edge connector itself. Do any of those add-on shield things give such surge-protection to the edge connector? . . . might be a good product idea.

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