You might not actually be connected to ground. You have DC going from the power supply to the notebook. Depending on how the power supply is isolated or not isolated, grounded or not grounded, there may not be a direct connection to an earth ground.
Just to be sure, I ran it past a couple of my ESD experts here.
Connect your ohm meter between the ground wire you have coming out of that USB cable, and the ground pin on the AC power plug (with the AC power cord unplugged). If it's less than 1 ohm, you're good to go.
I don't know what flavor notepad you are using, but I have a number of Lenovo Thinkpad power supplies on my desk right now, and i noticed that they have a TWO-WIRE UNGROUNDED (and unpolarized) AC plug. I also have some ancient Dell ones with 3-wire cords. Obviously, there's no point in ohming out the Thinkpad ones as there is NO input ground. The Dells do have the ground continuous (1.2 ohms) to the shell of the DC power plug. However, these are REALLY old (from XP PCs) so your results may differ.
@mhrackin: ...and i noticed that they have a TWO-WIRE UNGROUNDED (and unpolarized) AC plug.
1,000 curses-- you are of course 100% correct -- in fact Ivan came bouncing into my office about 30 minutes ago saying the same thing -- and as soon as he said it I remembered that my notepad also has a 2-pin power plug.
@Max...sorry to rain on your parade (or pee on your fire) but I would say 100% of all the brick type laptop and other power supplies I have ever taken apart (and there have been a few) have been switching types with the output isolated from the mains.
A mini-tower desktop computer might be different - those power supplies usually have a connection between the mains earth and the case of the PC....but I am not sure whether this will extend to the USB shield, I will check mine when I can.
Your solution might be to just switch your power supply off rather than unplugging it. Of course you should also check if the power supply ground goes all the way through to the output.
The best solution would be to get a mains cable with a proper 3-pin plug, cut the IEC end off (preferably while it is NOT plugged in :-), strip it back a bit, and cut off and insulate the white and black wires (which is what I think you have in the US) leaving the green earth wire only - and connect that to your anti-static mat. This does assume you have a spare power outlet where you are working, and that G the G does not want to use said outlet while you are electronicking...
PS to avoid the white and black wires shorting, cut them off different lengths. Then get some pliers and pull the insulation so you don't have wire ends sticking out. Then insulate them with tape. As the Irish would say....To be sure...to be sure...
@David: ...The best solution would be to get a mains cable with a proper 3-pin plug, cut the...
This is what I was planning on doing (except using plugs that are designed for you to wire up yourself) until Wnderer suggested using the existing banana plugs on the wristbands/mats along with these $7 ground plug adapters.
@David: ...The best solution would be to get a mains cable with a proper 3-pin plug, cut the...
One possible problem with this approach is that if you cut the banana plug off the lead, you might lose the 1M Ohm resistor (these are sometimes mounted in the babana plug itself) -- that's another reason why Wnderer's solution is favorite.
..."It's your Australian accent" When I phone my mom in England she says "oh, you sound so Australian".
Thanks for the segue into my favourite story. Let me say (for the readers) that like in any country the accent of the spoken language (English in the case of Rhodesia/Zimbabwe) fills a spectrum. In Zimbabwe the range is from very close to the Queen's English (which I suspect David uses) to a middling South African accent. The South African accent in its extreme can be as harsh or evn harsher than a broad Australian accent. My accent, for several possible reasons including the fact that I lived in South Africa for 13 years, tends strongly to the South African.
When I first got to Canada there was no internet as we know it, and I wanted some data on some IC or another. I phoned the company in California, requested that the data be mailed to me and proceeded to give my address, ending with the usual flourish- "Ontario, Canada". "Oh," said the lady I was speaking to, "that explains your accent!"
@ antedeluvian "Ontario, Canada". "Oh," said the lady I was speaking to, "that explains your accent!"
South African accent mistaken for Canadian? LOL! Some accents are more readily identifiable; I once met a young lady from Scotland (she was an HP sales Engineer back before the word "Agilent" was even a gleam in a marketeer's eye) with a most beautiful Scottish accent that was a pleasure to hear.
Even though I no longer say "Eh?", after having lived in Texas USA for the last 17 years I still get asked "Are you Canadian?" I can't hear any difference between the way I talk and my native-born colleagues, other than one with a very pronounced Texas drawl. And contrary to myth, Canadians never did refer to that rock band as "Zed Zed Top".
@Zeeglen... " I once met a young lady from Scotland....with a most beautiful Scottish accent that was a pleasure to hear."
When I worked for an international airlines telecomms company in Harare (Zimbabwe) there was a lass in our Nice (France) office who used to sent me messages to phone through to her mom who lived in Harare. (This was way pre-internet.) The first time I did this I fell in love with her mom over the phone....she had the most beautiful southern Irish accent. I never met her but it was always a pleasure to phone her to pass the messages on.
I once rang a guy in Australia whom I had never spoken to before, After he'd spoken for about 10 seconds I said "You're from Zimbabwe, aren't you?" Astonished, he admitted he was....but I find the Zimbabwe accent very distinctive.
@Antedeluvian: A light Irish lilt begorrah, or even Welsh, look you.
Have you ever heard a "Geordie" accent from the Tyneside area of England -- pretty close to the boarder between England and Scotland in the scheme of things -- I love that accent -- to me it always sounds a bit like they are singing (plus they have a great sense of humor).
@studleylee I still keep a A/D converter I bought from Analog Devices that cost me $100 in 1984. I zapped it.
An engineering lab actually had a carpeted floor. Was supposed to be anti-ESD carpet, but the installer got it wrong, and it had to be sprayed weekly with some kind of chemical. Back then we did not have heel straps or wrist straps.
Anyway, on a cold dry winter day in the Great White North, a colleague had just installed the 1st of 10 samples of his brand new ASIC into the socket. It was in a ceramic package with a metal top. We fired the board up, then we wondered how warm the ASIC was running. My friend reached out to feel it - I said "Static!" but it was too late. We could hear the 'snap' of a strong ESD discharge.
He said "It's not very hot." Then a few seconds later "But it sure is getting hot now!"
Love it! I know the song, but the video of him explaining how he came to write it was interesting!
I should explain that I am an English-born Zimbabwean, but I learned Afrikaans after being ridiculed in a history class at school for not being able to pronounce "Bezuidenhout" a well know Afrikaans surname (it's "Ber-zayden-hote", but I said something like "Ber-zewden-howt" causing the whole class to crack up. Later I worked on a South-African island for a year and got almost fluent..
@Duane: In most US wall sockets, the screw that holds the outlet plate on is grounded. If that's the case, you could just connect to that screw for your earth ground.
But they I still have the probem that the wall socket is quite a way from the table -- unless I attach a loong piece of wire -- and I don;t fancy attaching and detaching that wire each time I want to play with my electronics...
Hi Max : I get over stretching the colied cable of the wristband by having a multiple socket strip, on a lead from the wall socket, in England these are very cheap from Ikea. The soldering Iron and powers supply go into two of the free sockests leaving me with two other sockets for wristband and antistatic mat.
Max, the use of the USB and the use of the power strip are NOT mutually exclusive! It would make sense to use the power strip regardless, just to reduce the excess bending over (although perhaps the exercise is beneficial!). I'd still vote for plugging directly into the U-ground hole rather than depending on the combined continuity of the series chain of alligator clip to USB shield wire to PC USB connector through PC internals to DC ground of power jack to power supply, thence (maybe) to the U-ground of the power cord into the AC outlet! Far too many points of failure there (and of the most unreliable system element: interconnections!).
I did something similar when I had to set up on a table that was inconvineiently far from a wall socket. Since I needed a multi lead outlet strip with a long cord to power the equipment, I attached the cable from the antistatic mat to a ground on the outlet strip (which was located on the far side of the table). I then attached the lead from the wrist strap to a banana jack at the grounding point on the antistatic mat (which was on the edge near the front of the table). This minimized the stretching of the wrist strap cord and the whole thing could be moved fairly easily by unplugging the outlet strip from the wall and rolling it (and the cables) inside the antistatic mat.
In general, grounding yourself through a piece of (consumer grade) electronic equipment for ESD control seems like a not so good idea. You are making assumptions about the goodness of that ground and assuming the equipment can withstand discharges into that point. If you are sure only the wriststrap connection touches the "ground" point, then currents are limited by the resistor in the strap anyway and less of a worry. If you grab the "ground" to make your connection, you could potentially make a direct discharge at that point.
Having said that, Tek scopes I have used in the past had a "grounded" banana jack on the front panel which I plugged into for ESD management. My thinking was since it was industrial gear, Tek designs robust equipment, and the point was probably put there for that purpose, it was fine.
If you are only dealing with isolated portable gear, I think it is more important to equalize potential to the gear, rather than to ground. .I have clipped onto grounds of gear in these cases. In this case, some (all?) soldering ground tips are grounded, so beware when soldering.
@Sanjib: Wow!!This is a cool little gadget!! Really appreciate the idea!
It really is, although the ~$7 is a complete rip-off for something that can cost only a fraction of a dollar to make -- but it really does work perfectly for what I want, and it (well, "they" because I bought two) are a one-time buy that should last me the rest of my life ... so what the heck :-)
Just to follow-up to say that these $7 ground plug adapters are GREAT. On the one hand I agree that $7 is a lot of dosh for a small piece of plastic with onely one metal prong -- on the other hand (as I mentioned to zeeglen) they are a one-time buy that will last me the rest of my life.
I was using them last weekend to ground my wristband and antistatic mat -- and they are SO MUCH BETTER than the dorking around I was doing before (happy dance)
@max: that is good to hear! On a possibly related subject: what disappeared from the "most commented" list that allowed the hoary old blog about appliances muttering behind our backs to reappear at the bottom of the list? I could have sworn that there was one at 102....
@mhrackin: On a possibly related subject: what disappeared from the "most commented" list that allowed the hoary old blog about appliances muttering behind our backs to reappear at the bottom of the list?
Why, it's strange you should ask, but by some strange quirk of fate it was this very column.
So what else did you check? How about your "home away from home" office? I don't know how recent the building is, but even in very new commercial space, I've found poor grounding practices that can result in significant ground differences between separate branch circuits even in the same room! I recall some recent postings on "Tales from the Cube" (on a sister site) that identified this as root cause of a number of strange occurrences.
@mhrackin: I recall some recent postings on "Tales from the Cube" (on a sister site) that identified this as root cause of a number of strange occurrences.
Hmmm -- the main tower in my office keeps on locking up for no apparent reason -- we've scanned it for malware and viruses --- we've run burn-in software to stress the machine and wee've also run deep memory tests overnight -- nothing shows up. I wonder...
Having just returned from the EMC Symposium, I'm reminded that there is, as Bruce Archambeault will tell you, there's no such thing as ground except perhaps in this case, for safety.
Too often, we use the term "ground" when we really mean "return" as in current returning to its source. Ground is a reference voltage. Current shuld not flow through a ground wire at all. When it does, you have samety and EMC problems.
The purpose of the wrist band is to provide ahigh-resistance (leakage path) from you to whatever you're working on. So if your circuit is floating and you're connected to the low side of its power supply, you should be OK. If the power supplye is indeed connected to the ground lead of the AC mains, then that's better.
Some years ago, I was installing a new hard drive in my desktop PC. When I powered it up, the power sypply fan came on, but nothing else. I had zapped the motherboard and needed a new one. Since that day, I always wear an ESD wrist strap.
@Martin So if your circuit is floating and you're connected to the low side of its power supply, you should be OK.
Also a good idea to connect a scope probe ground to a floating circuit as the first connection so that the circuit is no longer floating. I've zapped MOSFETs by connecting the probe tip to the gate first before the ground.
Max, I should have been more clear. The insulation on the ground wire of all four of my wrist straps failed, exposing the wire inside. On one of them, the insulation is turning into a kind of black goo. It got all over my hands. On the other three, it just loked like the insulation was stripped away, but I surely didn't do that.
@MeasurementBlues: The insulation on the ground wire of all four of my wrist straps failed, exposing the wire inside. On one of them, the insulation is turning into a kind of black goo. It got all over my hands.
Uggh -- remind me not to shake hands with you again.
Are you sure it's goo from the insulation that got all over your hands ... and not goo that was already on your hands being transferred to the insulation?
I think what everyone's waiting for is Wireless ESD. This would be a wireless method (no wrist or footstrap), of discharging ESD via one of the wireless consortiums that will allow the ESD we build up to power our phone to tablet. That would be a shocking development!
@seaEE I think what everyone's waiting for is Wireless ESD.
Also wireless oscilloscope probes. No cables hanging everywhere to trip over. Maybe we could kickstart and get some suckers er, investors interested in both. Product launch scheduled for next April first.
@Reinhardt: Your idea sounds good a first look, but are you sure our laptop is really grounded? Many laptop PSUs I have seen have only a two pin power plug, no protective earth pin.
If you read the comments below starting from the beginning, you'll see that my suggestion "crashed and burned" for thsi very reason -- it would work with a tower computer with a 3-pin plug and a grounded power supply, but that's not what I've got.
However someone offered a really good solution -- use a power strip with some banana plug to ground adapters, then oplug the banana plugs on the strap & mat inrto ths strip.
There's lots of stuff going here, but let me try to clarify some things.
When working on the something like a laptop, there are really two options of grounding for ESD purposes.
1. Ground all conductors and dissipative materials (people, product, worksurface, etc) through an electrical ground (third wire). This is the preferred method for electronics manufactures because the electrical ground is where other equipment (soldering iron, scopes, etc) used in the production environment if grounded, but not always available in "field" applications.
2. If grounding to the electrical ground is not possible, you can use equipotential bonding. Equipotential bonding connects all conductors and dissipative materials in the environment together. If you are working on something such as a laptop, you would use an alligator clip to connect the wrist strap to the housing of the laptop.
Both methods essentially do the same thing in creating an equipotential balance between all items and personnel. ESD events can only occur when there is a difference in the potential. Note that only conductors and dissipative materials can be grounded, insulators require ionization to control ESD.
Based on this post we are going to make some samples of a USB to banana jack adaptor to see how this would work. The adaptor will allow a standard wrist strap to be connected to the USB.
When breadboarding it can help to do all your work on a new cookie baking sheet. The raised edges keep small parts contained within your work area, and since your wrists can rest on the raised edges everything is at the same potential as the worker. Just be sure to touch the cookie sheet first when starting a session, and maintain contact with the cookie sheet.
@zeeglen: When breadboarding it can help to do all your work on a new cookie baking sheet. The raised edges keep small parts contained within your work area, and since your wrists can rest on the raised edges everything is at the same potential as the worker.
This is really good advice -- especially for younger people -- I have a young lad in mind (a friend's grandson) who is just starting to play with the Arduino -- his family doesn't have much money, so splashing out on earth straps and pads and those banana-to-power adapters would be out of his range -- also teaching him the discipline to use them correctly would be problamatic -- but the cookie sheet idea woudl be perfect for him -- I'll tell him when I see him next week.
ESD is tricky stuff, not only does it vary seasonally (the classic example of walking across a rug in the winter and then touching a grounded device) but also it varies geographically (Albuquerque, New Mexico is so dry that special precautions must be taken in manufacturing facilities). Regarding a simple home ground, I must say that I'm a little uneasy discharging unwanted high voltages into the moidst of a (presumably) well grounded laptop computer.
Why not plug the banana plug into the grounded third prong (after confirming that the outlet is properly grounded) of an outlet?
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