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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

#21

Post by lotsofmangos »

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…

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.

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

#22

Post by baxter001 »

thrownaway2424 wrote: post #12
pmalynin wrote: post #4

Explanation: Camera's have capacitors that charge up in order for the flash to happen. They are usually quite powerful. Now during the discharge (aka flash) what you have is very high energy electrons flowing across the wire creating aa magnetic field, coupled with the electric field of the electron you get a mild EMP. And if it is light sensitivity then it should be tested with a bright continuous light

The entire purpose of a camera flash is to create a directed electromagnetic pulse.

I am SO going to start referring to flash-lights as directed electromagnetic pulse generators, albeit ones with higher than normal pulse durations.

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

#23

Post by thrownaway2424 »

djmanning wrote: post #18
thrownaway2424 wrote: post #12

Earlier quoted context omitted.

The entire purpose of a camera flash is to create a directed electromagnetic pulse.

The entire purpose? Not really. I think it has something to do with a mess of directed photons.

Do you discern some difference between "light" and "electromagnetic radiation"? Because the former is a subclass of the latter.

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

#24

Post by falcolas »

djmanning wrote: post #18
thrownaway2424 wrote: post #12

Earlier quoted context omitted.

The entire purpose of a camera flash is to create a directed electromagnetic pulse.

The entire purpose? Not really. I think it has something to do with a mess of directed photons.

For a "that's the joke" - light is on the EM spectrum, so a flash directing light will direct an EM pulse. :)

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

#25

Post by lotsofmangos »

eternauta3k wrote: post #17
thrownaway2424 wrote: post #11

That comments thread contains a head-smacking quantity of ignorance. "Is it the light or the EM pulse?" What?

He's asking if it's RF interference or just the light.

RF interference is long wavelength light and the successful filter was blue-tack, so probably not.

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

#26

Post by jarvist »

lotsofmangos wrote: post #15
thought_alarm wrote: post #8

Why would a switched-mode-power-supply chip be photosensitive?

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…

I think it's more likely to be the other way round, a lot of plastics are semi-transparent to IR, all block UV extremely strongly (as you start ionising electrons).

For instance, black PVC electrician's tape is entirely transparent to near-infrared, I use this to cover Xenon flashbulbs & still have an infrared-sensitive trigger fire from them.

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

#28

Post by eternauta3k »

lotsofmangos wrote: post #25
eternauta3k wrote: post #17

Earlier quoted context omitted.

He's asking if it's RF interference or just the light.

RF interference is long wavelength light and the successful filter was blue-tack, so probably not.

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

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

#29

Post by jarvist »

pjc50 wrote: post #19
thought_alarm wrote: post #8

Why would a switched-mode-power-supply chip be photosensitive?

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 casin…

Epoxy resins are pretty transparent by themselves, opaque ones have additional materials or dyes added.

Most dyes (also aromatic organics) are not active (i.e. transparent) in the near-IR.

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

#30

Post by lotsofmangos »

jarvist wrote: post #26
lotsofmangos wrote: post #15

Earlier quoted context omitted.

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…

I think it's more likely to be the other way round, a lot of plastics are semi-transparent to IR, all block UV extremely strongly (as you start ionising electrons). For instance, black PVC electrician's tape is entirely transparent to near-infrared, I use this to cover Xenon flashbulbs & still have an infrared-sensitive trigger fire from them.

That was my first guess as well, the only reason I discounted it was that then I would expect the effect to happen more often. I could be entirely wrong there however.

edit - ars, I'm out of replies, but thanks for that. I think you are probably right.

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