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A Xenon flash will cause the Raspberry Pi 2 to freeze

raspberrypi.org

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Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#81

Post by userbinator »

swamp40 wrote: post #13

A xenon tube is a spark gap. 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 lig…

From this large picture,

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

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#82

Post by hueving »

Johnythree wrote: post #58

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…

This is not the same thing. The cause is from the burst of light, not EM.

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#83

Post by jakobegger »

scythe wrote: post #80
tdicola wrote: post #33

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: A…

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…

The problem with your theory is that, as others have noted, the effect seems to happen with a red laser pointer as well.

To interfere with the electronics, the wavelength only has to as large as the band gap in silicon (as someone else has noted, around 1.1 eV). This means that IR light (and all visible light) can cause the interference too.

A strong enough light source will lift a lot of electrons from the valence band across the band gap into the conduction band, effectively turning a transistor into a conductor for the duration of the flash. Since the sensitive part seems to be related to the power supply, it's quite plausible that this leads to the voltage fluctuations on the power rail.

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#84

Post by falsedan »

ChrisGranger wrote: post #34
eternauta3k wrote: post #28

Earlier quoted context omitted.

RF is not light and that's a pointless remark. But right on your second point.

Radio waves and light are both electromagnetic radiation. Loosely speaking, RF is light.

Are tomatoes quinces?

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#85

Post by TheSwordsman »

hueving wrote: post #82
Johnythree wrote: post #58

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…

This is not the same thing. The cause is from the burst of light, not EM.

What if I told you that light is EM?

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#87

Post by tacojuan »

tdicola wrote: post #62
noonespecial wrote: post #50

Earlier quoted context omitted.

Are you sure that's not induced current from the power spike required to operate the flash or the spark-gap inside the xenon tube? You've got the gear set up... would you mind terribly repeating the experiment but blocking the light with cardboard or something?

Alright I put the Pi 2 in a cardboard box and held the flash at the same spot (but the box obscures the light). It keeps running just fine and doesn't have the nasty spike. Definitely is something light related.

So this would be easily rectified by using a case for the pi?

Re: A Xenon flash will cause the Raspberry Pi 2 to freeze

#90

Post by Sanddancer »

tacojuan wrote: post #87
tdicola wrote: post #62

Earlier quoted context omitted.

Alright I put the Pi 2 in a cardboard box and held the flash at the same spot (but the box obscures the light). It keeps running just fine and doesn't have the nasty spike. Definitely is something light related.

So this would be easily rectified by using a case for the pi?

A case would fix it, but a cheaper fix would be to just put a dab of nail polish or other lacquer on chip U16, which seems to be the culprit.
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