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A Hidden Threat To Handhelds
Logic Bomb writes: "An article from the San Francisco Chronicle focuses on a lawsuit against Palm, but talks about a larger issue: static and handheld computers. Basically, as computing equipment becomes smaller and more likely to be carried around, major damage from static becomes a serious threat. As the blurb at the end of the article says, it takes 3500 volts for a human to feel a shock, but only 200 to potentially scramble a microchip." We already mentioned the lawsuit, but this has more information about the supposed risks to your motherboard.
It must have been my imagination that hurt when I plugged that paperclip into the wall outlet.
it takes 3500 volts for a human to feel a shock, but only 200 to potentially scramble a microchip.
excuse me? it depends on the current flowing and stuff.. for example, I got shocked by 240v two days ago, and i bloody well fealt it.
stuff
Class B has nothing to do with static electricity- it is just about intentional and unintentional radiation derived from the normal operation of the electronics.
I'm not even sure a (single) static discharge would show up on an EMI scan (which is done for class B certification) It would probably show up as a slight increase in the baseline noise level, but not push it beyond the class B limits.
"As the blurb at the end of the article says, it takes 3500 volts for a human to feel a shock, but only 200 to potentially scramble a microchip."
You can say the same thing about water - it takes quite a few drops for humans to notice that it's raining, but just one well-placed droplet will fry your motherboard. Do you see me suing Toshiba because I can't use my laptop by the pool?
What's your damage, Heather?
He said that damage attributable to static electricity causes losses to the global electronics industry in excess of $45 billion per year. The estimate, based on a sampling of electronics companies, includes the cost of damaged goods and their replacement, and field service for equipment repair.
;)
I wonder if the Damage by static is the default option in the returns database of these manufacturers
Partly wrong....you can become an electrical conductor at any voltage if the conditions are right. Besides, it takes a combination of the right voltage pushing a high enough current to hurt or kill you. 100mA conducted through the body is enough current to kill the average person. When you get zapped by static electricity, there is a potential there of about 13kV....but there is a very small amount of current....that is way you don't get hurt.
"No Comm, No Bomb"
--CTH
--Got Lists? | Top 95 Star Wars Line
A serial port (RS-232 interface) that can be damaged or destroyed by the static electricity from a user is poorly designed.
Mea navis aericumbens anguillis abundat
All they'll have to do is have a grounding connector pin placed slightly ahead of the data and power pins on the connector. Hot swap drives do this today, why can't handhelds?
-- Minds are like parachutes... they work best when open.
It doesn't take 3500 volts for a human to feel a shock, naturally. It takes 3500 volts for a human to feel a static discharge, which is what the story asserted.
www.timcoleman.com is a total waste of your time. Never go there.
You are confusing ESD (electrostatic discharge) with EMC (electromagnetic compatibility). They are very seperate issues.
is a serious problem. It IS possible to design interfaces which offer useful resistance. But it is suprisingly hard to design and build in practice and it causes problems throughout the electronics industry. To build a Port (USB, serial, whatever) which can resist electrostic discharges requires that you use most of the following :
Protective devices which can dissipate the energy. The risetime from Static discharges is very fast and overwhelms all but the best protective devices.
Drivers/receivers which are hardened against static (the major semi manufacturers who do such chips do now make some - but they tend to cost more
Careful mechanical design to further reduce the problem - arrange that the "grounds" always touch first - preferably through a few hundred thousand ohms of resistance.
Optical isolation (although many people fail to understand the limitations of this technique - the stray capacitance between the isolated section and everything else is almost always high enough to allow static damage to happen.
More importantly manufacturers need to test their designs properly using realistic test models. Much equipment - including from the big name manufacturers pays little or no attention to this issue. Presumably for cost reasons - although if the right measures are "designed in" from the start the premium is going to be pretty small. It's interesting to compare the serial interface from a top branded PC with a functionally-identical interface from some serious telecomms kit.
I'm an engineer - not a lawyer. But I do know that I'd hate to have to do the finger pointing in the "Palm v motherboards" issue. If forced to comment I'd say that both sides should share the responsibility.
AJB
--Got Lists? | Top 95 Star Wars Line
Stephen Wise, a San Francisco accountant, said he smelled smoke and heard a crackle of static after putting his Palm Vx in the cradle. Wise claims his computer was damaged, forcing him to replace his PC during the busy tax season.
Great example to give... certain to frighten every non-tech out there. Of course, how many times have you 'smelled smoke' from an ESD? Sheesh.
'Life is like a spoonful of Drain-O, it feels good on the way down but leaves you feeling hollow inside'
As for your other point:I completely agree, although I believe one of the PC manufacturers who the users claim can be affected by this problem is DELL, which as far as I'm concerned isn't known for their poor design. I would certainly expect them to have sufficiently grounded serial ports.
--CTH
--Got Lists? | Top 95 Star Wars Line
I believe that the poster is unfamiliar with today's microelectronics. Yes, static electricity has gotten a bigger deal as the geometries have gotten smaller. However, do you remember the days of the PC clones with static strips nearby? If you didn't touch the static strip and were walking on carpet, you could fry the entire computer (my friend toasted two motherboards that way, by way of the keyboard). How often do you hear about this kind of thing today? (Expected answer: every now and then) How does this compare to the days that electronics were much less pervasive? (Expected answer: It happens less often)
The reason behind this is that chip manufacturers have been working on modelling the kinds of static electricity that humans produce (human body models) and machines produce (machine models), and designing I/Os to accomodate the new parameters.
Yes, some companies take their chances, ignoring static electricity (and there are some performance benefits to doing that), but these are risks that most of us can weigh.
I doubt that this is the case at all. It would be very difficult to get a charge to travel in one of the serial ports wires and not get grounded on the way there. Furthermore, the serial port, being one of the available external ports, is generally very well protected from static discharge. The real problem here is that nearly every integrated mobo has the serial port contained in the northbridge/southbridge chipset, so discharge to the port means discharge to a critical IC in the computer as well.
Good mobos will have protection right at the port, including zener diodes and possibly MOVs (MOVs break down and conduct at high voltages, zeners prevent the voltage going above a certain point, in this case above or below 13 volts or so).
The actual IC will generally also contain similar protection.
But this isn't an issue of whether it happened, or is even a remote problem. This is the "The coffee burnt my lap" problem. In our increasingly litigious society we sue people for not warning us of possible problems. All computer and electronic devices say "Static electricity may cause damage to device." What these laywers apparently want is Palm to put in big bold letters that "This device may act as an additional path for static electricity to damage your computer or other palm attached device." Which is silly. The user, had they read their documentation, knows that both devices are sensitive to static. Do they think they are immune to it by ganging the devices up?
Another lowest common denominator problem...
-Adam
And the amperage also has an effect.
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Serial ports (I'll stick with RS-232 and 485 - I'm most familiar with them) use voltage & logic shifters to handle the conversion of the port voltages to internal logic voltages. For years, most RS_232 ports on PCs used the MC148x or MAX232 type serial inetrface chips - got news for you, NONE of these chips have ESD hardening. RS-485 ports were even worse - they used a chip called a 75176 - those things would blow when you pulled one out of a pack to insert it in place of a blown chip. Ever notice how many cards with 1489type interface ICs had them in sockets? There was a reason - I've replaced a fw in mine.
I've designed embedded boards for Home automation and our boards used RS_485 which gives you long distance (1000-4000') over twisted pair at decent speeds for system control. The original design (which I didn't do and which was done BEFORE ESD variant chips were available) used the 75176. I had customers calling for replacements all the time. Those long twisted pair cables connecting nodes together were asking to induce surges AND when folks wired them up with bare hands and no static strap - they induced charges into the wires connected to all other nodes!
Maxim IC came to the rescue by developing the MAX232E and MAX485E which were ESD hardened interface ICs for RS-232 and 485 respectively. These things are amazing. One article I read had a guy sending massive (like 40kV) pulses into these chips and they survived. They are rated for +15kv and man do they work. When we switched to these chips (our main controller had both RS_232 and RS-485) our serial bus failures went away. TO dtae I have not had a customer complain about a failed ESD hardened chip from Maxim. Only problem is they ARE more expensive - about double. But WELL worth it IMHO.
Obviously - anyone handling motherboards or any other bare electronic board without using a static strp is an idiot - you're just ASKING for it - and um if you unplug your PC and then ground your strap to the case - it doesn't help much sinc ethe case is only grounded when its plugged in! You have ot ground your strap to somethign thats grounded!
But ddesigning your system with external ports and not using ESD haardened ICs and surge supressing devices is just asking for trouble - but these things cost money. Surge problems are worse than ESD often. But the savings in customer satisfaction and warranty repair costs often outweigh the extra pennies - but its hard to measure.
As for static straps - its amazing how people hate them so. I managed a 10k sq ft data center with almost 700 servers, from small $5000 machines to monster Auspex boxes costing millions. We implemented a policy that every tech in teh room had to wear a static strap on theri wrist, shoe, or static shoes and had to test the device when they entered (testers at every door) This was for ISo compliance but it was also smart. A single board for an Auspex might cost $50,000 to $250,000!!!! Yet I constantly had to police the situation and hassle people because they refused to wear the straps. The worst were the Sysadmins - they figured since they didn't touch teh cards themselves it was OK, yet they were plugging serial cables into exposed serial ports to hook up root terminals (before we had a networked root term setup) It was amazing the resistance I encountered for such a simple thing.
The bottom line is, if you are design a device for end use - spend the $$$ on ESD and surge suppression. If you are a tech or even a hobbiest working on teh guts of a PC or even hooking UP a PC that might not have said ESD protection, wear the strap or shoes. All it takes is one zap and thousands of dollars go up in a spark!
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It's unbelievable... There's no doubt that both palm and Motherboard Manufacturers should do better when designing for ESD resistance, but users should be careful rather than sue... but this, I guess is the american way...
--CTH
--Got Lists? | Top 95 Star Wars Line
IIRC from my early Computer Engineering classes, all it takes to damage a circuit is +5 volts or static electricity. It seems like it was something around +10,000 volts of static electricity before we as humans feel it. I think that's right. I'll have to dig out my old books. They showed a demonstration video of a typical engineer in a simple short sleeved button down shirt (plain) and simple tie. He neutralized himself (voltage equalization IIRC). Then someone (also equalized) held the tie at shoulder level just away from the 1st guy's shirt. He let go and let the tie brush against the guy's shirt. They then measured how much static electtricity was generated. It was more than enough to damage a circuit board. Mind you, +5v probably won't toast a board right away but it could easily cause damage that shows up down the road. IIRC correctly of course. It's been a while since I had that class.
From the article: "You cannot expect people to become more educated," Smith said. "The equipment has to be perfectly safe."
See, here's why there are so many lawsuits and bad stuff (like the DMCA... do I get extra karma points for mentioning the DMCA in a completely unrelated discussion? Ah well, nevermind) happens.
Expectations. If you don't expect people to be educated, then they never will be. Instead of having so many lawyers going "my poor client didn't knew thay you shouldn't stand at the top of a 15-foot metal ladder in the middle of a thunderstorm, while installing his TV antenna", you should get more judges who think "Serves you right for being such an idiot. Next case!".
I agree that sometimes consumers must be protected from Evil Corporations Who Want To Take Over The World, but there's a big difference between: a) not letting oneself get screwed by the Evil Corporations etc.; and b) blaming the Evil Corporations etc. for each and every stupid accident that could have been prevented with a little common sense.
As usual, let's blame the lawyers instead.
Tongue-tied and twisted, just an earth-bound misfit, I
Learning to fly, Pink Floyd.
I would consider it a componant of the radiation the device emits...
But the device isn't emitting it- the person is the source of the static discharge. The static charge is absoulutely *not* generated by the operation of the device- If it was, then I agree that it would have to be taken into account.
For static discharge, the FCC class rating of the device is a non-issue. It is a concern safety-wise, but the FCC rating is about emissions, not about safety. There are other, separate, certifications about safety.
I've taken part in EMI testing for class B certification- static discharge is not a part of it.
It's not about AC vs. DC at all. The article is referring to static discharge, which is the equilization of differing voltage levels. Here's the google cache of the first decent explanation I dug up on google. I'm sure you can find more yourself.
https://www.eff.org/https-everywhere
Careful mechanical design to further reduce the problem - arrange that the "grounds" always touch first - preferably through a few hundred thousand ohms of resistance.
Ummm... how the hell is ground to be effective with that kind of impedance? Ground potential should be equal.
Yes and no. It takes about 0.183A (IIRC) to cause your heart to go into an irregular pattern, resulting in a heart attack. Higher current loads through the heart are different; They cause it to stop, and (likely) start beating again. This is the principle used to start your heart again after it's stopped beating.
Much has to do with the resistance in ohms of your skin when you have the electrical shock applied; Are you doing something stupid like working on a grounded metal roof in wet bare feet with power tools (case study in class, that one), etc etc etc.
Many variables are at play here; Power is dangerous and something to be resepected at any level. I zapped myself real good with 25kV once, never again .. :)
..don't panic
Have you shocked yourself on a speaker? A Mouse? A Keyboard? Each of those devices can roast the computer it's attached too. I don't remember seeing people run around sueing the manufacturers of those devices. The same 'ground yerself before you touch' principle holds up for any device attached to a computer.
As a rock-in-roll Physicist once said, No matter where you go, there you are.
3 months into my new Visor, I had one final hard reset incident, and after that my USB port became non-functional (I also have a USB Zip drive that I use several times a day, so I can tell you precisely when it died). Hardware support happily arrived and replaced the system board in my Dell, but I was wondering what could possibly by the problem that caused the failure in the first place?
Eventually, I exchanged the Visor, and brought the new one back to work. I put it in the sync cradle. *reboot*.
At this point, I knew it wasnt the Visor, and I knew it wasnt the Dell, but it was obviously some combination of the two. As an experiment, I went a week with a grounded anti-static wriststrap wrapped around the back of the sync cradle. I made a point of touching it before I set the Visor in the cradle. Lo and behold, no more hard resets!
I decided to make this modification more or less permanent. I found the ground cable in the cradle, and the corresponding copper spring clip where it mates to the Visor. Using a trusty set of hemostats, I bent and extended it up to where it is the first bit of the cradle that touches the Visor. On the other end of the sync cable, I ran a little pigtail wire from the metal sheath of the male USB port to a screw on the back of the case.
This has the benefit of directing any static directly to the ground of the case, instead of routing the discharge through the USB controller, to *it's* ground.
Now, I dont really know whether or not this worked, because static shocks are pretty rare here in the summer (St. Louis, MO, where the humidity rarely drops beloe 75%). I'll have to wait until this winter, when the central heat kicks in, and the relative humidity in the office is about 15% before we see whether or not I've improved my sync cradle.
This space for rent.
"it takes 3500 volts for a human to feel a shock, but only 200 to potentially scramble a microchip"
.000005 amps and you will never notice, but one hundred volts at five amps will light your ass up!
When will the world catch on that it is not the volts that matter, but the amps! I can hit you with a million volts at
It's rather silly that the plastic plates are not available separately. But I guess they have calculated that they make more money selling entire new screens or even new PDAs...
I'd call that level of repairability as useless. People really should pay more attention to this kind of problems.
Think "programmer with screwdriver" or "phd with soldering iron". Common sense and intelligence often seem to be inversely proportional.
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Things are more complex than just the amount of voltage you get through your body. One can die from 400V and survive from a shock of 10000V. How come? The current is very important and so is how well you are grounded.
(The funny thing is, the 220V (110V US) we use daily is less dangerous than the 24V in your phone when ringing.)
How much current is dangerous? Well, 5 milliamperes can be felt, 10 will be felt and hurts, 15 will really hurt, 30 will freeze you on to the current source. And we are just talking about milliamperes people.
42 + 1 = 42
You are confusing ESD with EMC
I just can't keep up. I know about RMS and ESR, but who are these new guys?
--
As a matter of fact, I am a lawyer. But I play an actor on TV.
If you're running ANY electronics in an environment like that, you'll see it die, eventually, if not sooner. It doesn't matter what you connect, once you put a wire outside of the computer, it's another route for things to get zapped.
--Mike--
Lacking <sarcasm> tags,
...where do you buy yours?
Static discharges can destroy many an integrated circuit if there is improper internal protection. Think about it, if one external pin of a device is connected to the gate of one MOSFET (which can happen sometimes), and that pin suddenly accumulates charge through ESD, it won't take much for the oxide to break down between the gate and the substrate, and then you've got a chip that won't work.
Say the ESD pulse happened on the power (or gnd) line. Suddenly, across your entire chip, you have a 200V difference between power and gnd for a fraction of a second. Unless you've specifically added extra circuitry to cope with this (and any knowledgable designer will), something's gonna blow, even if it is for just a fraction of a second. With a 200V potential difference, it doesn't take long for 77 angstroms of SiO2 to break down.
Standard ESD protection within a chip consists of control circuitry that will turn on a low-resistance path between any two pins whenever the potential difference becomes too great. The plan is to make the current flow through a large internal ESD bus, rather than through the delicate core circuitry of your device.
Of course, a good defense is to prevent static discharges from ever reaching your device. Anti-static bags provide a conductive path around the outside of the bag, so that the least resistive path is not through your device, but rather around the outside of the bag. They are in general a very good idea, because there is no telling what kind of ESDs you can encounter during shipping and handling, whereas when a component has been installed somewhere, the ESD that it will encounter can generally be predicted.
PS - Charge is measured in Coulombs, capacitance is measured in Farads.
It may look like I'm doing nothing, but I'm actively waiting for my problems to go away.
--Scott Adams
Thirty years ago I worked for Digital Equipment Corp, as a systems testing engineer. Our department did hardware and software testing of all systems configurations that went out the door, I worked on the LSI-11 based stuff. One of the tests we had to do was for ESD, or static discharge as it was there called. The test consited of drawing an arc from any exposed surface of the equipment, to pass it had to withstand an arc of at least 5000 volts (IIRC). The tester was a high voltage power supply that could be adjusted to as high as 15kv (it was limited to a few MA). The probe was an old VTVM high voltage probe with the tip replaced by a metal sphere about 6-8" in diameter. The tester would crank up the voltage and pass the sphere around the outside of the computer to draw an arc from various locations as the computer was running a systems diagnostic. There had to be no systems failures. Usually we didn't fry anything (I can't remember ever destroying anything), but sometimes the diagnostic would fault or the computer would re-boot when the arc was drawn. I wonder if any of todays PC's could pass such a test? (Not running windows!, probably get the BSOD when you draw an arc!).
It's only a "transient" state during the mating process. Once fully mated you want the impedance to be as low as normal.
But ideally you want the "first touch" to be a high impedance. That dramtically slows down the rise time - which is likely to prevent damage.
Most likely static "sources" can be effectively discharged to safe levels by a leakage impedance of megohm or so - and within a few ms.
AJB
You can now find Manufacturers who boast of serial interface chips with 15kV ESD tolerance - and better - and using a more relaistic test model.
Maxim are one example. They do some nice application notes on the subject too.
Go to http://www.maxim-ic.com/
Look for "interface and interconnect" under "products" - then click on "product trees"
You'll see several Tx and Rx families boasting of 15kV protection. Follow the links and you will find data sheets and app notes which go into quite a lot of detail.
NB - I will never again design another single-sourced Maxim chip into one of my designs ever again. And if the alternate source is Linear Technology then it might as well be single-sourced. I am not alone in thinking like this!
AJB
>The risetimes of static can generally be handled just fine with good diodes
Very true. But there are plenty of crap parts out there - which certain manufacturers suggest are suitable for this kind of application when they aren't. And because many designers regard this kind of thing as a "black art" and don't seem to know when they're been offered rubbish.
>Most companies opt for an all-MOS technology these days
Indeed. However even that need not be a problem.
I agree about the bipolar stuff BTW - its just that sometimes you want/need to use the MOS stuff - and with good reason.
AJB
...damage attributable to static electricity causes losses to the global electronics industry in excess of $45 billion per year...
Would that include lightning strikes? (If I remember gradeschool science correctly, lightning is static electricity on a big scale...)
$45 billion dollars? that sounds kind of high - Any chance Bill Gates will off himself scuffing across the carpet in his slippers next year?
Cheers,
Jim in Tokyo
-- My Weblog.
But 16 week lead times and minimum quantities of 5000 are fun!
-- ;-)
Kuro5hin.org: where the good times never end.
>But 16 week lead times and minimum quantities of 5000 are fun! ;-)
16 weeks I can (just about) cope with. When they routinely start looking at next year's calender - then I get worried.
What's worse is when they've promised you 32 weeks or whatever, you've waited 30 weeks and you've only got two weeks to go - and they suddenly phone you to say that they're not going to deliver for another 12 weeks.
The best comment I ever saw goes "Maxim won't deliver this year - LT won't deliver this decade"
AJB
I do electrostatic discharge and interference tests for a living. We can produce electrostatic discharges ranging from a few hundred volts to over 300 thousand volts (landing aircraft) in house. We also radiate products with radio frequency interference from a few hundred kilohertz up to the microwave range. Sometimes we just listen to what products put out as well.
Most of the devices we test are safety-critical. Your home computer likely will never be seen in our lab. We recently conducted a test where a product in its box was shocked with a 300 kV static discharge. The spark (besides traveling three feet) went through the box, in one terminal of the item, and out another.
While charges on your body are not nearly that strong (the highest you'll build up likely is 25-30 kV), you shouldn't laugh at them.
Many modern manufactuers no longer include safety components ment for repair technicians. Often saving less than a fraction of a cent (in bulk), the lack of these parts make it an extreme risk to open things like microwaves and televisions. Not to be dismal, but don't open these items unless you know what you are doing; I have heard of experienced technicians putting their hand in the wrong place and regretting it.
Quick and simple.
On another topic: Your comment violated the postercomment compression filter. Comment aborted
Lose the lameness filter, Taco.
Yes, believe it or not, modern computers are quite sturdy. I've beveled the edges of my Duron with homebrew watercooling tech., I've passed current through my heatsink (melting the contact points to boot), hooked up who knows what to the serial ports, and currently my tv card is being fed via telephone wire because I ran out of coax. On top of that, I unplugged and then plugged back in my cdrom drive while my computer was running, producing a bright arc of electricity and a seemingly dead motherboard, which I revived the next day. These people are either unlucky that their computer fried, bought cheap crap, or they want cash (probably the latter).
The best way to accelerate a windows box is at 9.8 meters per second square.
$5.00 per component may be cheap when buying a motherboard or Palm as a consumer. It's quite a different matter for the manufacturer. When making millions of motherboards a year, multiply the number of units made by $5.00 and you get a large chunk of cash that any electronics manufacturer will refuse to spend, especially in the highly competitive, low profit margin computer industry.
Add five dollars to the manufacturing cost of a motherboard? Ain't gonna happen. Most managers go ape-shit when asked to put in a component that increases manufacturing cost by 15 cents per unit.
Looking at my Palm m505, it's apparent that there is some decent ESD protection. The connector that connects the Palm and the cradle has two metal hooks that contact two metal latches on the Palm before the gold connector pins make contact. I'd bet good money that they're grounded. There's also a ferrite cylinder attached around the cable to the USB port. Between that and the aluminum case, I'd say that it's pretty hard to static-zap your Palm or system in the process of cradling your palm for a sync. But that's just the Palm m500 & m505. Other Palms have different connectors.
Meldroc, Waster of Electrons