That is fun, reminds me of the 'yelling at the drives slows them down' video.[1]
A Xenon flash will cause the Raspberry Pi 2 to freeze
31–40 of 135 posts
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#32Earlier quoted context omitted.
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.
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 atomic scale, radio frequency is motion of electrons at the scale of antennas, but they both generate electromagnetic waves quantized as photons.
edit - darkmighty. Electromagnetic radiation at radio frequencies is popularly known as light in contexts such as speed, but not in contexts such as colour.
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#33Oh 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!
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#34Earlier quoted context omitted.
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.
Radio waves and light are both electromagnetic radiation. Loosely speaking, RF is light.
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#35Earlier quoted context omitted.
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.
It probably needs a short pulse. A normal light or a heater is constant and doesn't trigger anything. (AC vs DC.)
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#36Earlier 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…
RF refers to specific frequencies of radiation, which are not popularly known as light at all. Radio is usually in the MHz range to a few GHz (10^6-10^9 Hz). Light starts a hundreds of Terahertz (10^14 Hz). The behavior is qualitatively different at usual scales due to quantum mechanical behavior (light is difficult to emit/absorb coherently -- it's more particle-like) at high frequencies.
A photon striking a semiconductor will probably displace an electron if given an adequate bandgap, creating a voltage spike (which is nonlinear -- i.e. the problem isn't a propagating terahertz wave obviously). An incident radio wave will cause voltage spikes through coherent induction in the wires (i.e. they act as an usual antenna).
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#37A 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…
To the downvoters of the above comment: if it's technically incorrect, say so. I don't know if it is or not, but it's certainly not an offensively worded comment. When you downvote rather than respond, you are actually spreading ignorance. A downvote is an effort to mute. A half-muted incorrect technical comment will encourage far more ignorance than a properly corrected, visible one. Don't encourage ignorance.
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#38I just ordered two of these, and they will arrive on Tuesday.
Makes me sad because I'm imagining a Raspberry Pi 2.1 release in the near future now...
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#39A 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 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.
Re: A Xenon flash will cause the Raspberry Pi 2 to freeze
#40I just ordered two of these, and they will arrive on Tuesday. Makes me sad because I'm imagining a Raspberry Pi 2.1 release in the near future now...
The update will be a piece of black tape or epoxy over that component.