Naked Science Forum
Non Life Sciences => Technology => Topic started by: Jim Vincent on 25/10/2008 11:10:25
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Jim Vincent asked the Naked Scientists:
My wife has an mp3 player that stops erratically. But when I use it the
operation is flawless. Could her body's electrical field be the cause of the
player's erratic operation?
What do you think?
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No. Check the battery contacts.
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A very strong static electrical charge can build up in the clothes you wear, depending upon what the clothes are made of and how they're layered, and this static charge can discharge via the body, which is a reasonable conductor, and damage modern electronic equipment that uses very low voltage components. Most modern electronic equipment is regarded as charge sensitive and isn't supposed to be handled without some form earthing to the body, most often by a conductive wrist-strap attached to an earthing point, to allow the build up of static to drain away.
It is possible that your wife is building up a strong enough charge that it's disrupting the device.
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Nah .. Static can't disrupt a device. It can destroy a device but only effects chips which are not terminated ... they do take precautions during assembly of items but I have soldered in many a CMOS device without earth straps etc.
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Sorry, but I've seen it happen consistently too many times while doing Tech Support on computers. One of the best examples was a person who would regularly crash their system just by touching the keyboard - it was fine for me and other people but as soon as they tried it again - crash. Had to get them an earthed, conductive seat covering.
I'm afraid that the fact that you may have worked on CSDs without earthing really proves nothing unless you ensured that you were highly charged and un-earthed before you started working. If you're not charged before starting the work then there would be no effect, regardless of whether you're earthed or not.
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Lee is right that it is possible to disrupt electronic equipment by electrical discharge but it is very unlikely once the equipment is assembled. Pumblechook is right that chips are sensitive to static discharge but are relatively much safer once soldered on to a PCB. It is a matter of luck, though, whether you can get away with handling such devices without taking precautions of using an earth strap and working on a (slightly) conductive benchtop. It can depend on your clothing material and the air humidity. Most devices are sample tested to ensure they can withstand a certain amount of electrostatic discharge. This is typically done by discharging a 100pF capacitor through a 1.5kohm resistor into each pin (with respect to the other pins); the capacitor is charged to a voltage (and the chip is supposed to survive both polarities) which has a specified value - typically this is 4000V but it can be as low as 500V or as high as 8000V. This test is called the Human Body Model and most modern semiconductor devices are expected to pass this though it is not always possible. There is another test which checks out sensitivity to machine handling (lower voltage but lower resistance). The devices are usually irrevocably destroyed by such discharges. If not destroyed they are certainly damaged badly.
Once assembled most of the pins of devices are not accessible and any that are have some low impedance path to protect the device from discharge. However a large enough discharge (Lee's Keyboard issue perhaps) could just cause a soft data error even if the devices are protected. If is still not very likely though, and in my experience a discharge that could pass between the keys of a keyboard would certainly be noticed by the user!
I would not rule out elecrical discharge but I think there may be other explanations that are more likely.
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Jim Vincent asked the Naked Scientists:
My wife has an mp3 player that stops erratically. But when I use it the
operation is flawless. Could her body's electrical field be the cause of the player's erratic operation?
While I couldn't absolutely rule out static electricity, in the real world I think it fairly unlikely (unless there's a particular reason to suspect static, eg if your wife was forever getting shocks off things, or had clothing "clinging" to her etc).
I own an early Sandisk MP3 Companion mp3 player and it just freezes randomly because the firmware is buggy. I have to remove the battery-compartment lid to reset it. Sometimes it'll go flawlessly for 8 hours, other times it'll freeze several times in an hour. As far as I know, I've got the latest firmware, so I just have to live with it :-(
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Munchausen's Syndrome by Proxy with a computer, I suspect.
People can be very inventive in their ways of avoiding work. What better way to get a break from work than to disable your computer until the poor Tech Support guy has mended it.
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I think it is highly unlikely static has got anything to do with it. People jump to all sorts of conclusions. I can't see that one person is more 'electric' than another. The only factor can be the clothing warn which won't always be the same.
Reminds me of the countless times I have heard that people's terrestial TV reception is poor because it is raining
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Rain could always get inside the (cheapo) junction box on the antenna and cause some signal loss. It's not a totally barmy idea.
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I nearly added that comment.
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Reminds me of the countless times I have heard that people's terrestial TV reception is poor because it is raining
My previous housemate's digital terrestrial TV reliably failed during and after heavy rain. The signal on those two multiplexes was marginal at best, and with the aerial inside the roof and pointing almost parallel to the roof tiles, I suspect the wet tiles was enough to drop the signal below the workable threshold.
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You can get effects like that but the point is the weather is often blamed when it is nowt to do with the weather. Wife says very often if telly pictures are poor or disturbed and we happen to have bad weather ..'it must be the weather'.... But there are many times when pictures are poor when the weather is pretty good. we happen to live at then end of a long chain and the chances of faults and problems are much greater then someone who is London say. Lighting can trip the mains to part of the chain but the weather cannot affect how the TV signal goes through the air. It can disrupt satellite signals but that works at more than 10 times the frequency and it is quite rare.
I could bore for Britain.
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It can disrupt satellite signals but that works at more than 10 times the frequency and it is quite rare.
It has been a major factor in allocating satellite channels and powers to some Equatorial countries with high rainfall statistics. If you work with marginal receiving equipment and are near the edge a the footprint, you can expect noticeable degradation during heavy rain in the UK.