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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

#111

Post by tomkinstinch »

noonespecial wrote: post #70
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.

Thanks! Well done. Photoelectric it is. Now I wonder what color its most susceptible to...

The responsivity of silicon (and other semiconductors) by wavelength is pretty well characterized[1]. Any data sheet for a silicon photodiode will include a similar plot, and as photodiodes are just diodes (granted, operated in reverse bias), regular diodes will have a similar response if light can get past the part package. Photodiode junction doping and geometry are optimized to make them useful as optical devices, but they're still VERY close to regular silicon diodes.

This property of diodes can be used in a fun way: LEDs emit light, but they can also be used as photodiodes[2]. It's easy with a microcontroller pin that can act as both a digital output and analog input. LEDs are of course not optimized for this use (small sensor area, the package may absorb useful light particularly in the UV, phosphor if present may get in the way), but they can be used as photodetectors. There's even an Arduino sketch[3].

1. http://image.slidesharecdn.com/lect12-photodiodedetectors-13...

2. http://www.merl.com/publications/docs/TR2003-35.pdf

3. http://playground.arduino.cc/Learning/LEDSensor

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

#112

Post by crb3 »

swamp40 wrote: post #59
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…

My money is still on an electromagnetically coupled pulse onto either the 3.3V or ground rail. 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...

It can and did happen, as the afflicted chip was the SMPS controller.

At last, a use for all those write-protect stickers we collected for floppies...

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

#113

Post by seba_dos1 »

Narishma wrote: post #106
pervycreeper wrote: post #86

Slightly OT: is it now possible to run a completely free OS on this new version? I've been getting contradictory info on this so far.

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?

Original Raspberry Pi needs user to provide non-free firmware blobs on SD card to even boot the CPU. That's pretty non-free in any meaning I can imagine.

It seems like it's still the case with Raspberry Pi 2.

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

#114

Post by DonHopkins »

AlyssaRowan wrote: post #109
Sanddancer wrote: post #90

Earlier quoted context omitted.

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.

Handy tip! Which - just tested - seems to work for me, at least with a couple of coats of black nail polish, and double-checked with a high-end Canon flash and a random green laser pointer. (Of course your mileage, and nail polish, may vary.) I should change the hostname to nemi. ;) There's another 'shiny' chip on the board too, next to the HDMI port, U8 I think, but it doesn't seem to give a damn what you do to that…

Don't you get on the NSA's subversive person list for buying black nail polish?

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

#116

Post by pedrocr »

morganvachon wrote: post #107
pervycreeper wrote: post #86

Slightly OT: is it now possible to run a completely free OS on this new version? I've been getting contradictory info on this so far.

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. G…

> 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.

3-clause BSD (what's common these days) meets pretty much everyone's definition of Free:

https://www.gnu.org/licenses/license-list.html#GPLCompatible...

(The following licenses qualify as free software licenses, and are compatible with the GNU GPL.)

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

#117

Post by poizan42 »

pedrocr wrote: post #116
morganvachon wrote: post #107

Earlier quoted context omitted.

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. G…

> 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. 3-clause BSD (what's common these days) meets pretty much everyone's definition of Free: https://www.gnu.org/licenses/license-list.html#GPLCompatible... ( The following licenses qualify as free software licenses, and are compatible wi…

Not if you ask RMS: https://www.gnu.org/philosophy/open-source-misses-the-point....

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

#118

Post by Turing_Machine »

poizan42 wrote: post #117
pedrocr wrote: post #116

Earlier quoted context omitted.

> 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. 3-clause BSD (what's common these days) meets pretty much everyone's definition of Free: https://www.gnu.org/licenses/license-list.html#GPLCompatible... ( The following licenses qualify as free software licenses, and are compatible wi…

Not if you ask RMS: https://www.gnu.org/philosophy/open-source-misses-the-point....

"the GNU GPL qualifies as an open source license and most of the open source licenses qualify as free software licenses."

There are open source licenses that RMS considers non-free, but the modern (3 clause) BSD license isn't one of them.

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

#119

Post by Natanael_L »

e12e wrote: post #108
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.

I'm not familiar with the photoelectric effect - would this be susceptible to a laser (and if so, how weak a laser? A laser pointer?)?

Somebody else said a laser pointer works, but I can't confirm myself yet as I don't yet have a pi 2

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

#120

Post by [deleted] »

lotsofmangos wrote: post #32
eternauta3k wrote: post #28

Earlier quoted context omitted.

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

RF stands for radio frequency, and defines a band of electromagnetic radiation, popularly known as light, that is on a continuum of frequencies that above RF pass through visible light and on towards gamma rays. In simple terms, whenever something possessing charge moves it generates an electromagnetic wave associated with the motion and at right angles to it. Visible light is generated by motions of electrons at an…

[deleted]
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