Oh neat, I just reproed it with a Pi 2 and a Canon Speedlight flash. I'll put my scope on the power lines and see what's happening when you flash the board. Sounds like from the thread one of the power ICs is photo sensitive.
edit: Wow yeah, here's a look at the 3.3V power line when you flash the board, it drops almost down to 0V and then wildly fluctuates for about 100 nanoseconds: http://imgur.com/hG86pRy
edit 2: Another interesting measurement, with the board _totally unplugged_ and flashing it you can see a big voltage spike on the 3.3V rail. Up to 6-7 volts or so for a few nanoseconds: http://imgur.com/td262QK
I guess not only can you learn about electronics but also Einstein's photoelectric effect with the Pi 2!
The historical importance of the photoelectric effect is to demonstrate the relevance of the work function Ω. It works like this:
V ~ E_0 - Ω
where hf is the energy per photon and Ω is the work function of the target. If Ω > E_0, no voltage is produced. This provided the basis for Einstein's demonstration that energy is proportional to frequency (E_0 = hf), and won him the Nobel prize.
What does this have to do with xenon? Xenon lamps produce not only visible light, but also ultraviolet light, in fact, xenon lamps extend further into the UV than natural sunlight:
With this data we can determine that the work function of silicon (in the Raspberry Pi 2) is somewhere in the range of hc/(400 nm) < Ω < hc/(250 nm) or 3.1 eV < Ω < 5 eV. Using data from
From The Devouring Fungus, Karla Jennings, 1990, chapter 10, The Monster Turns… and Falls to its Knees, p. 211:
Another legendary debacle triggered by light hit at a highly publicized affair thrown by IBM, ironic considering that IBM is the master of the seamless image. D. E. Rosenheim, who helped develop the IBM 701, the first mass-produced modern commercial computer, recalled the famous faux pas, which occurred when the company held a dedication ceremony for the 701’s installation at its New York headquarters. Top-level executives, the engineering team, and a gang of reporters crowded the ceremony room
“Things went pretty well at the dedication,” said Rosenheim, “until the photographers started taking pictures of the hardware. As soon as the flash bulbs went off, the whole system came down. Following a few tense moments on the part of the engineering crew, we realized with some consternation that the light from the flash bulbs was erasing the information in the CRT memory. Suffice it to say that shortly thereafter the doors to the CRT storage frame were made opaque to the offending wavelengths.”
Those who do not know their history are doomed to repeat it.
Note for the kids: Yes, that's right, it says CRT memory. That's the same Cathode Ray Tube as found in non-flat-panel TVs and monitors, except we're using it as a high speed storage device.
Ironically, the wikipedia page for Selectron tubes actually has more useful information on Williams tubes than it's article does... http://en.wikipedia.org/wiki/Selectron_tube
This reminds me of an old Finnish engineering legend from the early days of Nokia. The guys had just built an important prototype of some network equipment (early GSM base stations IIRC), which was going to be demonstrated for the press. All tests and previous demos had gone fine.
But as soon as the demo for the press started, the machine crashed. The management was upset. Later, the reason was found to be some old EPROM chips that are erased using UV light, and the photographers' cameras had strong flashes that went through the tapes covering the "window" on the chip. This caused the program memory to be corrupted when a photograph was taken.
Interesting that the Finnish version of this story is about Nokia, GSM base stations and EPROM memory. The version from 1990 from The Devouring Fungus which I quoted in a separate comment is about the IBM 701 and CRT memory.
One of the standard tests to gain an EMC Compliance Certificate is a spark discharge test.
Any experienced engineer will have a Spark Generator (Car Ignition coil, spark gap and short Dipole) to test to see if his latest project misbehaves when confronted with Impulse Interference.
As an EMC Investigator I would always carry a spark generator to demonstrate to newby engineers why EMC Compliance is so important.
I've seen a spark from 50ft away crash or reset a microprocessor system. Just the static discharge from walking on carpet is often enough.
Reminds me of old EPROMs. You can buy special "light sensitive" transistors, but they're really just ordinary transistors with a window in the case, since ordinary transistors are light-sensitive. You can even use an ordinary 1N4148 diode as a solar cell, it just doesn't generate much power.
The fix is simple: apparently, you just have to cover U16, which controls the power supply.
There's nothing mysterious about this. Semiconductor gates are light-sensitive. There's usually carbon black in the plastic of plastic-packaged ICs to prevent interference from light. The opacity isn't perfect, though. For that you need ceramic or metal-encased ICs. Still, this is a rare enough problem that IC data sheets don't specify a maximum tolerated illumination level.
Try some laser pointers, especially towards the blue end of the spectrum where the photons have more energy. You may be able to trigger this effect by pointing at a specific IC.
A xenon tube is not a spark gap, in terms of the early radio receiver 'spark gaps' which were a primitive tuned circuit used to then feed an antenna (it wasn't the spark itself that was used for the transmission).
Sparks produce a broadband radio signal, that decays strongly with increasing frequency. Very little is present in the Megahertz region, which is why lightening doesn't interfere with FM radio that much.
Radio frequencies below the gigahertz or high megahertz region will not interfere with the Pi as the wavelength of these is too long to effectively couple into the short circuit board traces.
Xenon flash tubes are not that noisy in terms of unwanted RF. Apart from anything else, you wouldn't be allowed to sell such radiating circuits in consumer equipment.
A xenon flash puts out an enormous amount of blackbody light (high in IR and NIR) in a very short time frame (as short as 100 ns). Plastics are not very IR blocking by themselves. Silicon has a band gap of 1.1 eV. Any photons above this energy will be absorbed across the gap, and interfere with the circuitry. Firing a xenon flash close to something will result in an instantaneous light flux many hundreds of times larger than direct sunlight.
So the circuit might be designed to be resistant to any ambient lighting situations, but not to being flashed.
As a commentator mentioned below, U16 is a switched mode power supply circuit. It's analogue, and switching quite fast. It doesn't take much for it to be disrupted & mess up a few cycles, possibly even then triggering some protection circuitry on the inputs of chips down the line.
Blue tack, being an insulator, will be almost totally transparent to radio frequencies.
U16 appears to be in a WLCSP package (and others have noted that it is "shiny", which would also agree with the typical appearance of one), and WLCSPs do not have much of a package - they're essentially bare die that have had solder bumps attached to their top surface, and are mounted upside-down ("flip-chip" style) onto the PCB. It won't take much light intensity to cause photoelectric effects on a WLCSP.
Hi, you should have a look elsewhere in these comments where a HN user has reproduced it with his camera flash, but used a piece of cardboard to block the light and the Pi behaved normally.
Cardboard (and I'll wager the blue tack also) has negligible EM shielding effect, so I'd say that's pretty conclusive that it's a photoelectric problem.
A light flash is an EMP. Radio waves are light. They also, unless they are very short, pass easily through blue-tack. When they get that short they are basically becoming infra-red anyway. Then we have a wide range through the visible spectrum, up through UV, that blue-tack stops, until we start getting towards x-rays and blue-tack starts to become transparent again. This is caused by an electromagnetic pulse, but of one in or close to the visible spectrum, otherwise blue-tack would be useless.
edit :
The word light is commonly used as shorthand for variously the whole EM band, the near visible EM band and just the visible EM band.
If you are talking about the speed of light, it includes radio and gamma.
Discussing the colour of light on the other hand and you are referencing the visual system.
As soon as you start talking about visible light however, you are widening the definition of light again to include IR and UV and more, otherwise you would not need to clarify with the word visible.
edit 2 - darkmighty. I am not talking about the xenon bulb producing an RF EMP from the lamp flashing circuit, I am merely continuing the terminology used elsewhere in this thread, that a flash of visible light is also quite clearly a form of electromagnetic pulse.
edit 3 - foobarbecue. Radio as it gets shorter becomes microwave, then IR, then red, through green, past blue, goes to UV, then xrays, then gamma.
The new wave of single board computers really exposed me to the amount of failure that can happen at the electrical level. Growing up with large ATX boxes I'd never expect so many things to go wrong.
btw: anyone tried to light-freeze other devices (banana, orange, cubie, etc) ?
Question to HN: Does also the Raspberry Pi 1 B or B+ have this problem or is the Xenon flash problem specific to the Raspberry Pi 2 B? Is somebody willing to do this experiment/has done it?
All silicon is photosensitive to some extent. The power supply will be one of the few chips which is primarily "analog"; in particular it will have a bandgap voltage reference. That's exactly the sort of thing to be badly affected by a charge pulse from the flash. Glitching the power supply will then destabilise the digital logic it's powering.
The real question is how the light manages to get through the epoxy casing.
All chips are photosensitive and a xenon flash produces light from UV through to IR, so my guess would be that the plastic used for the casing on that chip is not entirely opaque to something at the top or bottom end of the visible spectrum, which is why most bright lights don't trigger it. At a bet, I'd say the top end, as otherwise radiant heaters would also probably kill them. Would be fun to play around with some filters and a flashgun and narrow down the frequency.
Not yet. Closed source binary blobs are necessary for booting and for accelerated video. In fact, it's the GPU that bootstraps the rest of the board when you first power it up.
There is work being done to write an open source driver for the GPU, with the blessing of the RPi Foundation and BSD-licensed code provided by Broadcom[1]. But I don't know if that will include the bootstrapping code, or how far along it is. Given that it is BSD licensed, it may not meet everyone's definition of "Free", but at least there is a good chance of having fully documented, source-available drivers in the future.
That's because completely free means different things to different people. Does it include the firmware/bios? Are you only concerned with what runs on the CPU?
[+] [-] tdicola|11 years ago|reply
edit: Wow yeah, here's a look at the 3.3V power line when you flash the board, it drops almost down to 0V and then wildly fluctuates for about 100 nanoseconds: http://imgur.com/hG86pRy
edit 2: Another interesting measurement, with the board _totally unplugged_ and flashing it you can see a big voltage spike on the 3.3V rail. Up to 6-7 volts or so for a few nanoseconds: http://imgur.com/td262QK
I guess not only can you learn about electronics but also Einstein's photoelectric effect with the Pi 2!
[+] [-] noonespecial|11 years ago|reply
You've got the gear set up... would you mind terribly repeating the experiment but blocking the light with cardboard or something?
[+] [-] scythe|11 years ago|reply
V ~ E_0 - Ω
where hf is the energy per photon and Ω is the work function of the target. If Ω > E_0, no voltage is produced. This provided the basis for Einstein's demonstration that energy is proportional to frequency (E_0 = hf), and won him the Nobel prize.
What does this have to do with xenon? Xenon lamps produce not only visible light, but also ultraviolet light, in fact, xenon lamps extend further into the UV than natural sunlight:
http://en.wikipedia.org/wiki/Xenon_arc_lamp#mediaviewer/File...
LEDs by contrast produce almost no UV light:
http://en.wikipedia.org/wiki/Light-emitting_diode#mediaviewe...
With this data we can determine that the work function of silicon (in the Raspberry Pi 2) is somewhere in the range of hc/(400 nm) < Ω < hc/(250 nm) or 3.1 eV < Ω < 5 eV. Using data from
http://journals.aps.org/pr/abstract/10.1103/PhysRev.127.150
http://www.sciencedirect.com/science/article/pii/00223697599...
we see that the work function of silicon is around 4.7-4.9 eV, which agrees well with our observations.
draws a little box
[+] [-] swamp40|11 years ago|reply
I have seen that happen plenty of times, but I have never seen a light flash disrupt a power rail like that.
I'm not saying it couldn't happen, just playing the odds...
[+] [-] fnordfnordfnord|11 years ago|reply
[+] [-] teddyh|11 years ago|reply
Another legendary debacle triggered by light hit at a highly publicized affair thrown by IBM, ironic considering that IBM is the master of the seamless image. D. E. Rosenheim, who helped develop the IBM 701, the first mass-produced modern commercial computer, recalled the famous faux pas, which occurred when the company held a dedication ceremony for the 701’s installation at its New York headquarters. Top-level executives, the engineering team, and a gang of reporters crowded the ceremony room
“Things went pretty well at the dedication,” said Rosenheim, “until the photographers started taking pictures of the hardware. As soon as the flash bulbs went off, the whole system came down. Following a few tense moments on the part of the engineering crew, we realized with some consternation that the light from the flash bulbs was erasing the information in the CRT memory. Suffice it to say that shortly thereafter the doors to the CRT storage frame were made opaque to the offending wavelengths.”
Those who do not know their history are doomed to repeat it.
[+] [-] BuildTheRobots|11 years ago|reply
Note for the kids: Yes, that's right, it says CRT memory. That's the same Cathode Ray Tube as found in non-flat-panel TVs and monitors, except we're using it as a high speed storage device.
Ironically, the wikipedia page for Selectron tubes actually has more useful information on Williams tubes than it's article does... http://en.wikipedia.org/wiki/Selectron_tube
[+] [-] ChuckMcM|11 years ago|reply
[1] https://www.youtube.com/watch?v=tDacjrSCeq4
[+] [-] exDM69|11 years ago|reply
But as soon as the demo for the press started, the machine crashed. The management was upset. Later, the reason was found to be some old EPROM chips that are erased using UV light, and the photographers' cameras had strong flashes that went through the tapes covering the "window" on the chip. This caused the program memory to be corrupted when a photograph was taken.
[+] [-] teddyh|11 years ago|reply
[+] [-] Johnythree|11 years ago|reply
Any experienced engineer will have a Spark Generator (Car Ignition coil, spark gap and short Dipole) to test to see if his latest project misbehaves when confronted with Impulse Interference.
As an EMC Investigator I would always carry a spark generator to demonstrate to newby engineers why EMC Compliance is so important.
I've seen a spark from 50ft away crash or reset a microprocessor system. Just the static discharge from walking on carpet is often enough.
[+] [-] hueving|11 years ago|reply
[+] [-] dietrichepp|11 years ago|reply
The fix is simple: apparently, you just have to cover U16, which controls the power supply.
[+] [-] adestefan|11 years ago|reply
[+] [-] Animats|11 years ago|reply
Try some laser pointers, especially towards the blue end of the spectrum where the photons have more energy. You may be able to trigger this effect by pointing at a specific IC.
[+] [-] rasz_pl|11 years ago|reply
[+] [-] mholt|11 years ago|reply
[+] [-] alephan|11 years ago|reply
[+] [-] swamp40|11 years ago|reply
If there's anything in this world noisier than a spark gap, I don't know what it is.
I think the first radio transmitters were spark gaps.
The energy flies thru the air, and is coupled onto the power line.
The power supply doesn't cope well with the oscillations, and hiccups.
I see the notes about U16 being photosensitive, but if it is a black epoxy like most IC's, I'm not buying that light gets into it.
It's possible that blue tack shields the EMP a bit.
[+] [-] jarvist|11 years ago|reply
Sparks produce a broadband radio signal, that decays strongly with increasing frequency. Very little is present in the Megahertz region, which is why lightening doesn't interfere with FM radio that much.
Radio frequencies below the gigahertz or high megahertz region will not interfere with the Pi as the wavelength of these is too long to effectively couple into the short circuit board traces.
Xenon flash tubes are not that noisy in terms of unwanted RF. Apart from anything else, you wouldn't be allowed to sell such radiating circuits in consumer equipment.
A xenon flash puts out an enormous amount of blackbody light (high in IR and NIR) in a very short time frame (as short as 100 ns). Plastics are not very IR blocking by themselves. Silicon has a band gap of 1.1 eV. Any photons above this energy will be absorbed across the gap, and interfere with the circuitry. Firing a xenon flash close to something will result in an instantaneous light flux many hundreds of times larger than direct sunlight. So the circuit might be designed to be resistant to any ambient lighting situations, but not to being flashed.
As a commentator mentioned below, U16 is a switched mode power supply circuit. It's analogue, and switching quite fast. It doesn't take much for it to be disrupted & mess up a few cycles, possibly even then triggering some protection circuitry on the inputs of chips down the line.
Blue tack, being an insulator, will be almost totally transparent to radio frequencies.
[+] [-] userbinator|11 years ago|reply
https://blog.adafruit.com/wp-content/uploads/2015/02/Pi_II_t...
U16 appears to be in a WLCSP package (and others have noted that it is "shiny", which would also agree with the typical appearance of one), and WLCSPs do not have much of a package - they're essentially bare die that have had solder bumps attached to their top surface, and are mounted upside-down ("flip-chip" style) onto the PCB. It won't take much light intensity to cause photoelectric effects on a WLCSP.
More info here: https://ez.analog.com/docs/DOC-2357
[+] [-] na85|11 years ago|reply
Cardboard (and I'll wager the blue tack also) has negligible EM shielding effect, so I'd say that's pretty conclusive that it's a photoelectric problem.
[+] [-] encoderer|11 years ago|reply
[+] [-] shortimer|11 years ago|reply
[+] [-] lotsofmangos|11 years ago|reply
edit :
The word light is commonly used as shorthand for variously the whole EM band, the near visible EM band and just the visible EM band.
If you are talking about the speed of light, it includes radio and gamma.
Discussing the colour of light on the other hand and you are referencing the visual system.
As soon as you start talking about visible light however, you are widening the definition of light again to include IR and UV and more, otherwise you would not need to clarify with the word visible.
edit 2 - darkmighty. I am not talking about the xenon bulb producing an RF EMP from the lamp flashing circuit, I am merely continuing the terminology used elsewhere in this thread, that a flash of visible light is also quite clearly a form of electromagnetic pulse.
edit 3 - foobarbecue. Radio as it gets shorter becomes microwave, then IR, then red, through green, past blue, goes to UV, then xrays, then gamma.
[+] [-] tonteldoos|11 years ago|reply
[+] [-] agumonkey|11 years ago|reply
btw: anyone tried to light-freeze other devices (banana, orange, cubie, etc) ?
[+] [-] mikerr|11 years ago|reply
[+] [-] wolfgke|11 years ago|reply
[+] [-] AlyssaRowan|11 years ago|reply
Don't have a B+ to hand, sorry. It might?
[+] [-] thought_alarm|11 years ago|reply
[+] [-] pjc50|11 years ago|reply
The real question is how the light manages to get through the epoxy casing.
[+] [-] lotsofmangos|11 years ago|reply
[+] [-] thrownaway2424|11 years ago|reply
[+] [-] sqren|11 years ago|reply
[+] [-] mikerr|11 years ago|reply
A laser (no EMP!) shone on that chip will also crash the Pi.
[+] [-] pervycreeper|11 years ago|reply
[+] [-] morganvachon|11 years ago|reply
There is work being done to write an open source driver for the GPU, with the blessing of the RPi Foundation and BSD-licensed code provided by Broadcom[1]. But I don't know if that will include the bootstrapping code, or how far along it is. Given that it is BSD licensed, it may not meet everyone's definition of "Free", but at least there is a good chance of having fully documented, source-available drivers in the future.
[1] http://www.raspberrypi.org/a-birthday-present-from-broadcom/
[+] [-] Narishma|11 years ago|reply
[+] [-] bitwize|11 years ago|reply
In light of Heartbleed and Shellshock, I propose calling this the Photon Torpedo vulnerability.
[+] [-] seba_dos1|11 years ago|reply
I see what you did there!
[+] [-] DalekBaldwin|11 years ago|reply
[+] [-] unknown|11 years ago|reply
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