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Author Topic: Is static electricity any danger?  (Read 1768 times)
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Hi,
I have an Arduino board mounted on to a extruded polystyrene foam "sculpture", that has considerable friction between parts. I've put insulation tape between foam and board, but as it's non-conductive it probably offers no protection from static charge. Didn't run the device yet with board mounted.

Is static charge dangerous to the board in situations like this? Is there a way to protect the board when the source of charge is all-around?
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In a word "probably".  You could possible shield the arduino by enclosing it within a grounded metal enclosure (zinc or aluminium box).  Your connection leads would be outwith the box and may therefore pick up the static.  Shielded leads using say fine microphone cable with shields grounded externally may be a solution.
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If you really worry, you put TVS devices (typically MOVs) between each input/output and ground. These are fairly affordable (similar to diodes) and don't degrade the signal noticeably, and are also safe to put on inputs, outputs, and power lines. Note that, if there's lots of static, the MOVs will be slowly consumed by static, and at some point, the protection will fail.
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The Atmel processor chips have built-in positive and negative clamping diodes on all the I/O pins that do offer some protection from ESD type events. These do however have limits of how much total energy (joules?) that they can safely dissipate. So I guess it's a matter of how 'bad' a static discharge situation you specifically have to deal with. I would just go ahead and let it be without any special added protection, and only deal with it if there is indeed a problem detected later.

Lefty

 
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Would connecting the Arduino logical ground to physical ground help?
« Last Edit: April 09, 2012, 01:45:47 pm by bibre » Logged

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Is static charge dangerous to the board in situations like this?
Static discharge is always a concern.

But keep in mind that static discharge is relative to the same thing that all voltages are relative to... COMMON.  Aka, Ground. 

As already mentioned, if your circuit was actually connected to EARTH ground then you would have a very well known common / GROUND connection.

I think it is very likely that one side of your circuit would have higher potential than the other, due to the polystyrene.  In which case, a voltage potential could develop between the sides of your circuit.... allowing an electro static discharge to, well, discharge.  You need to carefully ensure your entire circuit's common / ground is at the same potential at all times.
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static is a weird unpredictable thing, though in general you can charge 30KV and things work fine ... its when you discharge is when the stuff hits the fan (as little as a single KV depending on variables).

you are asking for trouble, but will it bite you? I dunno

I have spent 3 weeks making large chats, zapping crap with an ESD gun, its highly varible, but I would not choose to invite it. TVS's on everything gets expensive, offering grounds near inputs is effective, there is a balance
« Last Edit: April 08, 2012, 02:56:07 am by Osgeld » Logged


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You could also use 1M resistors to protect you IO pins from static electricity. That is 1M to ground not in series of course.
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Thanks for lots of replies!
Got the ventilation aluminum tape. Think I'll lay the polystyrene with it and isolation tape over, to make a bed for Arduino. I don't have much wires, so probably taping them too will do as shielding.

TVS - can anyone post a link or example name of what I should be looking for? Can it work for analog input (Piezo element to detect vibration)?
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I was going to mention using aluminized duct tape too, I've used it for several
projects, including lining plastic trays I keep parts in for projects. Kind of like
the pink nonstatic bags but more permanent.

Instead of MOVs, I think Transorb devices are better at handling ESD, and you can
get ones for protecting different voltage levels. These are actually like very low
inductance zener diodes. I don't think they wear out like MOVs. Can put them on
I/O lines that go to external switches, etc.

http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode

The other thing that helps, in conjunction with the clamping diodes built into
all CMOS microcontrollers, are small series Rs in the I/O lines. This helps limit
the current into the clamping diodes. For input lines, you can probably use 5-10K
ohms. For output lines, I use 220-330 ohms. I always use them anyways to
protect the lines from overvoltages and short circuits, not to mention ESD.
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Thanks! Another useful component smiley They seem to be cheap.
So basically I need to put one of breakdown voltage >6V between data and ground.
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I could be wrong, but I do not think that shielding is the answer to your potential issue. 
I would suggest electrically conductive connection between all the foam parts and then connect that "circuit'" to the arduino's ground.
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Insulating the board should help - the danger comes from the friction surfaces which get strongly charged up and can then deposit their charge onto nearby conductors via corona-discharge. On insulators the charge stays very close to the surface and hops on and off the surface.  It shouldn't travel through insulating film unless its very thin.  Beware of the insulating film itself building up a charge.

Most strategies to control static use slightly conductive materials or coatings which prevent charge build-up. That or an increase in humidity.
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I imagine the aluminum tape is good for that because its conductive and provides a path of least resistance for most stray spikes
I wonder if there is a way to test these methods without putting any parts at jeopardy
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Quote
the danger comes from the friction surfaces which get strongly charged up and can then deposit their charge onto nearby conductors via corona-discharge.

He should be able to get some idea about static charge buildup by turning out the
room lights [assuming nighttime, :-)], and rubbing his finger and various other
materials over the surface of the project. I am kind of surprised of how many
situations around the home where I've seen static sparks that way. Most notorious is moving the sheets on the bed. But I live in a very dry climate too. You never notice
unless it's pitch dark.
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