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Xenon Death Flash: a free physics lesson (2015)


If you occur to own a Raspberry Pi 2, congratulations: you’re additionally the proud proprietor of an smooth demonstration of the photoelectric form!

On the weekend, Peter Onion, a gradual of our boards and of Raspberry Jams in Cambridge, Bletchley and surrounding areas (viewed, costumed, within the background of this photograph on the Christmas CamJam), realized what we expect could perchance maybe be the most lovely malicious program we’ve ever bump into.

The Raspberry Pi 2 is digicam-apprehensive.

Peter’s malicious program epic got right here by the explain of our boards. He’d been proudly photographing his fresh Raspberry Pi 2, and had realized something irregular: at any time when the flash on his digicam went off, his Pi powered down.

The blip you're seeing here is what happens when you point a xenon flash at a Pi 2.

The blip you’re seeing right here’s what happens whereas you point a xenon flash at a Pi 2.

Jonathan has spent mighty of the morning emitting flashes and poking an oscilloscope. We’ve realized out what’s going on, and the factual recordsdata is that it’s entirely benign: your Pi is now no longer going to endure any permanent results from being flashed at.

Extra factual recordsdata: the form easiest happens below VERY explicit cases. Flashes of high-depth, lengthy-wave gentle – so laser pointers or xenon flashes in cameras – trigger the instrument that is accountable for regulating the processor core power (it’s the chip marked U16 within the silkscreening to your Pi 2, between the USB power provide and the HDMI port – which that you would be in a position to maybe recognise it because it’s reasonably shinier than the substances around it) to get hang of careworn and create the core voltage tumble. Importantly, it’s ONLY in point of fact high-depth bursts esteem xenon flashes and laser pointers that can trigger the instruct. Other intellectual lights – even digicam flashes using diverse technologies – won’t internet web page online it off. That it’s doubtless you’ll maybe perchance opt your naked Pi 2 within the sunshine for a picnic or opt it to a rave, and it’ll be perfectly sturdy. Appropriate don’t opt it on the crimson carpet on the Oscars. Jon is at the moment shimmering an 1800-lumen led gentle at a Pi 2 on his desk: now no longer a lunge.

This component that’s inflicting the instruct is in a WL-CSP equipment: a naked silicon die which has solder balls linked. Here’s a image of the underside of a identical equipment (considerably magnified) – every circle is a minuscule ball of solder:

underside balls

WL-CSP packaging is a in trend methodology for extra high-tech electronics parts, as it capacity no further packaging of the instrument is required. It is additionally the smallest bodily equipment that which that you would be in a position to maybe agree with, which designers of cell things (and folk making very tiny computers) in point of fact care about.

What’s inflicting the component to behave so oddly? It’s the photoelectric form, the place metals emit electrons when hit by gentle. The video under is a terribly factual tutorial on how that works.

What you’re seeing with Pi 2 and xenon flashes is the the same form, nonetheless in semiconductor fabric, now no longer metal. Semiconductors, esteem metals, own free electrons that could perchance maybe be ‘knocked off’ by photons. Photodiodes, solar cells and phototransistors all explain this form to contrivance. If you occur to’d esteem to study extra about how a solar cell works, there’s a obliging explanation right here at

Silicon junctions (the kinds that are accountable for making diodes and transistors and diverse such electronic miracles contrivance) could perchance also be ‘upset’ by this photoelectric form if it’s a ways smooth ample (i.e. if ample gentle of the factual energy [i.e. colour] is fired at them). This appears to be like to be what’s going down to our power provide chip – someplace within the advanced silicon chip circuitry there are some transistors or diodes that malfunction when hit by high energy bursts of gentle, inflicting the flexibility provide to ‘tumble out’, so the Pi reboots.

Jonathan is actively investigating precisely what happens when U16 is flashed with a high energy pulse from a xenon flash tube, and we are additionally having a inquire of at that which that you would be in a position to maybe agree with ways to create future manufacturing Pis proof in opposition to this instruct if we can – we know you esteem to determine on photos of them.

We own realized no evidence that ‘flashing’ your Pi2 with a xenon flash can trigger any staunch damage, nonetheless we aloof don’t counsel doing it (this could perchance maybe wreck or reboot, and this implies which that you would be in a position to maybe perchance irascible your SD card). I’ve mentioned it above, nonetheless it completely bears repeating, because I’ve viewed about a of you existing this within the boards and in comments sections in other locations: in trend every day gentle sources – e.g. intellectual daylight, indoor lighting, mad cyclists– don’t trigger this to occur, so please don’t difficulty! 

If you occur to would esteem to explain your Pi 2 in a anguish the place it could perchance maybe be flashed at, our recommendation is to duvet U16 (be particular that you get hang of the perimeters too) – the newest easy repair is to explain a runt blob of Sugru or Blu-Tak covering the total component (any individual within the boards inclined a pellet of bread: the most valuable yeasted malicious program repair we own got encountered), or simply attach the Pi in an opaque case.

Secretly, I’m compose of hoping for one other (in a similar trend benign) malicious program this abstruse. I esteem penning this compose of submit.

*Existing to the paranoid on Twitter: I wasn’t certain ample right here. We’re relating to ourselves, now no longer dissing you and your bike. We’re in Cambridge, and a great deal of us cycle (aggressively) to and from work: we’ve been shimmering our bike lights at Pis for quite loads of this morning, because they’re the brightest lights any of us own.

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