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Raspberry Pi 2 has a bug and it will shut down under camera flash!!!
posted February 17 2015 18:54.07 by Giorgos Lazaridis




As it seems, Raspberry Pi 2 is camera shy! No kidding. Here is what Peter Onion posted on the PI2 forum:

I have discovered that my PI2 is camera-shy !
Taking it's picture with a flash causes an instant power off !
I've done it three times now and same thing happens each time.
First two times I didn't realise what had happened as I wasn't looking at the screen at the time and only noticed a few minutes afterwards.
Third time I did it just to watch the screen.... Instant power off.....
Any ideas ?
PeterO


So, what happened? Is the Pi2 a useless piece of light-sensitive material? Can camera flashes permanently damage your Pi2? Can direct sunlight trigger the same bug? NO, NO and NO!

After hours of research (and tons of camera flashes) the buggy part was spotted.

Jonathan has spent much of the morning emitting flashes and poking an oscilloscope. We've found out what's going on, and the good news is that it's completely benign: your Pi will not suffer any permanent effects from being flashed at.

More good news: the effect only happens under VERY specific circumstances. Flashes of high-intensity, long-wave light -so laser pointers or xenon flashes in cameras- cause the device that is responsible for regulating the processor core power (it's the chip marked U16 in the silk screening on your Pi 2, between the USB power supply and the HDMI port- you can recognize it because it's a bit shinier than the components around it) to get confused and make the core voltage drop. Importantly, it's ONLY really high-intensity bursts like xenon flashes and laser pointers that will cause the issue. Other bright lights -even camera flashes using other technologies- won't set it off. You can take your naked Pi 2 in the sunshine for a picnic or take it to a rave, and it'll be perfectly solid. Just don't take it on the red carpet at the Oscars. Jon is currently shining an 1800-lumen led light at a Pi 2 on his desk: not a wobble.


In the following image you can see this part:



But what is this photoelectric effect? In short, when photons collide with metals, it may cause the metal to emit electrons because there are free electrons inside (which is actually what makes metals conductive). Same happens here but instead of metal the casing is silicon, which is a semiconductor, which also has free electrons which can be knocked off by photons.

As a matter of fact, there are many components which use the photoelectric effect for its benefit, such as a photodiode, phototransistos, solar cells etc. Here is a nice video which explains this effect:




And yes you can solve this problem very easily - Just cover the U16 with a small blob of Sugru or Blu-Tak.

And yes, there is absolutely nothing to worry about:

We have found no evidence that 'flashing' your Pi2 with a xenon flash can cause any real damage, but we still don't recommend doing it (it will crash or reboot, and this means you may corrupt your SD card). [...] Common everyday light sources - e.g. bright sunlight, indoor lighting, angry cyclists - don't cause this to happen, so please don't worry!

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