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'[PIC] STATIC anoyances..(?)'
2005\04\27@092612 by Mauricio Jancic

flavicon
face
Hi,
       I have the following problem. I have developed a dog feeder that has
a PIC inside. A photo can be seen at
http://www.janso.com.ar/Picture%20004.jpg - Top of the feeder, controller
only
http://www.janso.com.ar/Picture%20010.jpg - Top view, full feeder
http://www.janso.com.ar/P000982.JPG - Full at the shop (400K image)

       As you can see the case is made with a process called rotomoulding.
I don't know the specifics of the process and materials used but I can tell
you for sure that the cases come to the assembly area with lots of static
(i.e.. Plastics "stick" to them...)

       Now, the system has a RTC on it and a PIC (16C63B) the problem I'm
having is that some RTCs (DS1307) are being damaged and I think is due to
static....

       What do you think I should do?        

Mauricio Jancic
Janso Desarrollos - Microchip Consultants Program Member
spam_OUTinfoTakeThisOuTspamjanso.com.ar
http://www.janso.com.ar
(54) 11 - 4542 - 3519

2005\04\27@095946 by Spehro Pefhany

picon face
At 10:16 AM 4/27/2005 -0300, you wrote:
>Hi,
>         I have the following problem. I have developed a dog feeder that has
>a PIC inside. A photo can be seen at
>http://www.janso.com.ar/Picture%20004.jpg - Top of the feeder, controller
>only
>http://www.janso.com.ar/Picture%20010.jpg - Top view, full feeder
>http://www.janso.com.ar/P000982.JPG - Full at the shop (400K image)
>
>         As you can see the case is made with a process called rotomoulding.
>I don't know the specifics of the process and materials used but I can tell
>you for sure that the cases come to the assembly area with lots of static
>(i.e.. Plastics "stick" to them...)
>
>         Now, the system has a RTC on it and a PIC (16C63B) the problem I'm
>having is that some RTCs (DS1307) are being damaged and I think is due to
>static....
>
>         What do you think I should do?

How about an anti-static coating or wash? There are such chemicals sold
by electronics distributors such as Future, but you might want to try
having them washed in a liquid fabric softener (inexpensively available
from the supermarket).

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com




2005\04\27@102427 by Russell McMahon

face
flavicon
face
> As you can see the case is made nwith a process called rotomoulding.
> I don't know the specifics of the process and materials used but I
> can tell
> you for sure that the cases come to the assembly area with lots of
> static
> (i.e.. Plastics "stick" to them...)
>
> Now, the system has a RTC on it and a PIC (16C63B) the problem I'm
> having is that some RTCs (DS1307) are being damaged and I think is
> due to
> static....

Some or all of:

   Static control.
   Static protection.

A high humidity atmosphere will reduce electrostatic charge.
Many companies sell static control surface treatment products eg 3M.
Most are not adequate for delicate electronic product protection.
SOME clothes treatment fabric softener products will help.
High capacity Negative Ion Generators are available to neutralise
static charge.
Wiping all surfaces with a grounded conductive material will help.
Storage for a while after surface treatment will help.
Rubbing some plastics with some other materials or against each other
can generate static charge.
Transport and store in ESD discouraging containers and environment.

All workers must have ESD protective equipment in this sort of
environment.
Earth straps, bench mats, floor mats, heel grounders, negative ion
generators, ...
Ensure workers clothes and seating etc do not cause ESD.

If there is heavy electrostatic contamination then either you are
going to allow the workers to be charged by the product or the product
to be discharged by the workers.

An electrostatic meter will tell you when you have problems, if you
have cured them, and what remains. Can be very cheap & simple if
desired.

Butyl rubber roofing and pond lining material can make extremely cost
effective antistatic mats for floors and benches and transport boxes.
Conductivity depends on carbon loading (I think) and varies. Get
multimeter and insert two probe tips into sheet perhaps 2cm apart. ANY
conduction on any range means it is probably OK. Some Butyl rubbers
are VERY low resistance and a potential shock hazard as they then
constitute an earthed surface.

Use real ESD wrist straps or at least add say 1 megohm resistor in
ground lead to reduce shock hazard. DO NOT use plain wire to ground.

Protect ICs at all times AND protect connectors etc on finished
boards. Ensure staff know and follow ESD safe procedures. Provide
earthing points for staff to use when they sit or handle or approach
equipment (include resistors).

Ensure soldering and desoldering equipment etc is ESD safe. Also
ensure that if hand irons are used that tips do not have leakage
voltages on them - death to ICs.

Where should I send the invoice ? :-)


       Russell McMahon




2005\04\27@103939 by ThePicMan

flavicon
face
At 10.16 2005.04.27 -0300, you wrote:
>Hi,
>        I have the following problem. I have developed a dog feeder that has
>a PIC inside. A photo can be seen at
>http://www.janso.com.ar/Picture%20004.jpg - Top of the feeder, controller
>only
>http://www.janso.com.ar/Picture%20010.jpg - Top view, full feeder
>http://www.janso.com.ar/P000982.JPG - Full at the shop (400K image)
>
>        As you can see the case is made with a process called rotomoulding.
>I don't know the specifics of the process and materials used but I can tell
>you for sure that the cases come to the assembly area with lots of static
>(i.e.. Plastics "stick" to them...)
>
>        Now, the system has a RTC on it and a PIC (16C63B) the problem I'm
>having is that some RTCs (DS1307) are being damaged and I think is due to
>static....
>
>        What do you think I should do?

shield it?


2005\04\27@105234 by Mauricio Jancic

flavicon
face
> Some or all of:
>
>     Static control.
>     Static protection.
>
> A high humidity atmosphere will reduce electrostatic charge.
> Many companies sell static control surface treatment products eg 3M.
> Most are not adequate for delicate electronic product protection.

[SNIP]

> Where should I send the invoice ? :-)
>
>
>         Russell McMahon

Hi Russell,
       Not to avoid the invoice but even if I find your information very
useful that was not what I meant. I have electrostatic protection procedures
on the assembly area and all products leave the factory working and in
optimal condition.
       
       My question was because some of the feeders (1 out of 40~50) stops
working and in most cases the problem is the DS1307 that is damaged. If I
replace it, everything is up and working again.

       My theory is that ESD is being generated and when the user approach
the machine a discharge is produced trough the 7 segment displays that you
can see on the pictures in the OP links.
       
       So the problem I'm trying to solve is exactly how to protect the
feeder to ESD in the normal use... Should I connect the plastic case to
earth? Would it work?

Best regards....

PS: if you still feel compelled to send an invoice you can send it to

Mauricio Jancic
Lugones 3238 "B" - C1430ECN
Capital Federal
Republica Argentina

:)) Thanks Russell


Mauricio Jancic
Janso Desarrollos - Microchip Consultants Program Member
infospamKILLspamjanso.com.ar
http://www.janso.com.ar
(54) 11 - 4542 - 3519

2005\04\27@110901 by Alan B. Pearce

face picon face
> As you can see the case is made nwith a process called rotomoulding.
> I don't know the specifics of the process and materials used but I
> can tell
> you for sure that the cases come to the assembly area with lots of
> static
> (i.e.. Plastics "stick" to them...)

I suspect you will find that the static charge is "built in" to the plastic
by the rotomold process, which I suspect is a bit like the spun concrete
process used for large pipes and water tanks. Note that it is possible to
permanently have a static charge on plastic - this is essentially what is
done for the electret microphone diaphragm during manufacture. As such it is
difficult to get rid of it. I suspect that you will need to spray the inside
of the electronics chamber in your container with one of those spray on
coatings used to RF EMC proof items, and have the front panel suitably
shielded and grounded as well.

2005\04\27@111212 by Mauricio Jancic

flavicon
face
> shield it?
>

Yes... But what do I use to make the displays visible and still have
shielding...?

Mauricio Jancic
Janso Desarrollos - Microchip Consultants Program Member
.....infoKILLspamspam.....janso.com.ar
http://www.janso.com.ar
(54) 11 - 4542 - 3519

2005\04\27@120358 by Russell McMahon

face
flavicon
face
> Not to avoid the invoice

Only joking,of course.

> My question was because some of the feeders (1 out of 40~50) stops
> working and in most cases the problem is the DS1307 that is damaged.
> If I
> replace it, everything is up and working again.
>
> My theory is that ESD is being generated and when the user approach
> the machine a discharge is produced trough the 7 segment displays
> that you
> can see on the pictures in the OP links.

Is there any conductive path from the outside to the inside. Frame
around display, switches, other controls?

If the PCB was at ESD potentials is the DS1307 in the obvious path?

Can you introduce system ground into the area that users touch? (ie
grounding something conductive that may be floating at present.)

Can you kill it with a spark discharge gun or by charging up people
and zapping it with a finger?


       RM

2005\04\27@121926 by Josh Koffman

face picon face
I believe there are clear plastics or sprays that are conductive
enough to be used for sheilding. Maybe installing one of those over
the display and grounding it might work. Or, perhaps a nice thick
clear plastic window over the display would increase the breakdown
voltage enough that the user wouldn't be sending a shock through the
display.

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

On 4/27/05, Mauricio Jancic <EraseMEinfospam_OUTspamTakeThisOuTjanso.com.ar> wrote:
> > shield it?
> >
> Yes... But what do I use to make the displays visible and still have
> shielding...?

2005\04\27@122135 by Dave VanHorn

flavicon
face

Keep your impedances as low as possible on I/O, and place significant
impedance between the electronics, and the outside world.
Small caps inside those impedances, to swamp any energy that does get
through, plus steering diodes to bleed it off to VCC or gnd as
appropriate.  Build from dissipative materials, conductive may get
you in worse trouble from the magnetic field pulses when discharges happen.
Tie any unavoidable floating metal to circuit ground through 1k or so
to limit current.


2005\04\27@122302 by ThePicMan

flavicon
face
At 12.12 2005.04.27 -0300, you wrote:
>> shield it?
>>
>
>Yes... But what do I use to make the displays visible and still have
>shielding...?

Shield everything but the displays, they're made of plastic (good insulator) anyway.
You may wish to add a plexiglass screen in front of the display for higher insulation.




2005\04\27@130613 by David Minkler

flavicon
face
Mauricio,

Perhaps you could integrate a small piece of indium tin oxide coated
film as the window to your display and use conductive sprays elsewhere.  
I just Googled on < +"indium tin oxide" +film > and had a fair number of
hits.  I know that the people who manufacture display overlays for us
(essentially a fancy label) use these kinds of films on some of our
products.

Regards,

Dave

Mauricio Jancic wrote:

>        My theory is that ESD is being generated and when the user approach
>the machine a discharge is produced trough the 7 segment displays that you
>can see on the pictures in the OP links.
>        
>        So the problem I'm trying to solve is exactly how to protect the
>feeder to ESD in the normal use... Should I connect the plastic case to
>earth? Would it work?
>


2005\04\27@130733 by J. Gromlich

flavicon
face
You are probably going to have to ask your plastic molder to add
a static suppressant to the plastic mix. Usually this is a graphite or
other conductive material which has minimal effect on the plastic
properties, except to give it high-resistance electrical conductivity,
usually in the megohm range. Static charges dissipate, or at least
equalize, around the object.  You still should have some means of
grounding (earthing) the device, although in your application I can't
see any easy way to do that.

RJG.

>
> {Original Message removed}

2005\04\27@131250 by Wouter van Ooijen

face picon face
> Yes... But what do I use to make the displays visible and still have
> shielding...?

IIRC the goldmine has an LCD glass with build-in screening.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\04\27@141954 by J. Gromlich

flavicon
face
Put a little conductive flap /"protective cover" over the pushbuttons.
This could be clear plastic with conductive fill - it could give a nice
"integral" appearance to the panel.  The user has to lift this panel /
cover to reach the buttons - in the process he equalizes the charge
between the unit and himself. If some just walks up and touches the
cover over the LEDs they also get the charge equalized.  Adds another
part - and probably not a really cheap part - to the device, but is that
more expensive than recall-repairs?

RJG


> {Original Message removed}

2005\04\27@145153 by Dave VanHorn

flavicon
face

My first big intro to this, was when we took banking terminals
designed in Hawaii, to Las Vegas in the winter.
We did not do that well, resetting on E-Field from people walking by
at 10-15' distance.

Later versions did just fine on the show floor, in ABS plastic cases,
and I couldn't even zap them with my "special" shoes on.
Meanwhile, across the row, the guy from Diebold, with his stainless
steel ATM is out spritzing his carpet with water..
I did kill a competitor's terminal at the same show, just touching
the buttons. But I wasn't trying to, I just touched the keypad.

Honest.
:)


2005\04\27@161317 by Brent Brown

picon face
>  Now, the system has a RTC on it and a PIC (16C63B) the problem I'm
> having is that some RTCs (DS1307) are being damaged and I think is due
> to static....

Well, from the the photo the switches and LEDs *look* like they would have a
fair amount of distance from static fingers by the plastic insulation. Given all
the good suggestions so far on reducing the amount of static present, next
thing you should look at is hardware/software modifications to reduce the
effects of static zaps when they do happen.

For starters, switch inputs should have clamping diodes plus series resistors
before micro inputs. PSU rail should have zener or TVS overvoltage
protection, and generous capacitance after regulator.

Here's a few guesses at the problem...the DS1307 is a two wire device
right(?), which means it shares it's input (more static sensitive) with it's
supply pin - which might mean that if this device is being killed by static it
would probably be from coupling along the power supply line. We've talked
about zaps coming through switches and LED display - what about when the
user changes batteries? (if it uses batteries). Zaps coming through the
battery connections could be more likely than through the front panel. Or if
there is a situation when the user can touch the back of the PCB it would be
even worse.

Also think about less direct causes. What if simple corruption of the RTC
registers (or micro registers even) causes your software to misbehave and
you mistakenly conclude that the RTC is dead? It is more likely that ESD
onto or nearby would at first corrupt data before before causing hardware
failures.

Best regards, Brent.
--
Brent Brown, Electronic Design Solutions
16 English Street, Hamilton 2001, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell/txt: 025 334 069
eMail:  brent.brownspamspam_OUTclear.net.nz


2005\04\27@171807 by Richard.Prosser

flavicon
face

a) Store in an area with high humidity?
b) Dunk in an earthed  water bath before fitting pcb?
c) Flood area with static dissipating air (deionisers?)

Note - if the charge is developed in the manufacturing process (ie an
electret material), the static may "recover" itself over a short period of
time. So use as soon as possible after "destatification". And ensure the
sensitive devices are protected againgst static problems once loaded on the
pcb. - fit high value bleed resistors on sensitive inputs etc.

RP



Hi,
          I have the following problem. I have developed a dog feeder that
has
a PIC inside. A photo can be seen at
http://www.janso.com.ar/Picture%20004.jpg - Top of the feeder, controller
only
http://www.janso.com.ar/Picture%20010.jpg - Top view, full feeder
http://www.janso.com.ar/P000982.JPG - Full at the shop (400K image)

          As you can see the case is made with a process called
rotomoulding.
I don't know the specifics of the process and materials used but I can tell
you for sure that the cases come to the assembly area with lots of static
(i.e.. Plastics "stick" to them...)

          Now, the system has a RTC on it and a PIC (16C63B) the problem
I'm
having is that some RTCs (DS1307) are being damaged and I think is due to
static....

          What do you think I should do?

Mauricio Jancic
Janso Desarrollos - Microchip Consultants Program Member
@spam@infoKILLspamspamjanso.com.ar
http://www.janso.com.ar
(54) 11 - 4542 - 3519

2005\04\27@172533 by Richard.Prosser

flavicon
face

Where can I get these "special" shoes from? They sound like a "must have"
for trade shows.

RP



My first big intro to this, was when we took banking terminals
designed in Hawaii, to Las Vegas in the winter.
We did not do that well, resetting on E-Field from people walking by
at 10-15' distance.

Later versions did just fine on the show floor, in ABS plastic cases,
and I couldn't even zap them with my "special" shoes on.
Meanwhile, across the row, the guy from Diebold, with his stainless
steel ATM is out spritzing his carpet with water..
I did kill a competitor's terminal at the same show, just touching
the buttons. But I wasn't trying to, I just touched the keypad.

Honest.
:)


2005\04\27@172910 by Russell McMahon

face
flavicon
face
> You are probably going to have to ask your plastic molder to add
> a static suppressant to the plastic mix.

As an experiment you can try nickel spray - made for electrostatic
shielding. Too dear for ongoing use but it will place a nice metallic
conductive layer on plastic. Even placed on extremely thinly it will
make a surface conductive enough for this application.


           RM


2005\04\27@173914 by Mauricio Jancic

flavicon
face
Well... THANK YOU ALL GUYS.
Let me tell you a little more...

As someone said, there are corruptions occurring here and there, but until
now I was under the impression that this was caused by shocks (physical
shocks, people hitting the feeder, dogs anxious to eat*, etc) but in the
light of the newly damaged (not working any more) RTC I started to think
about ESD, which I didn't consider at all in the first place... My fault,
yes, but the be fair I didn't originally know where was the board going to
be placed...

Anyway, I will try to get a spark generator and test a few things. I don't
think ESD is getting in trough the pushbuttons, they have a 5~7 mm plastic
insulation...plus the insulation of the pushbutton (it has a custom made
cup).
On the other hand I don't know about the ESD properties of the 7 segment
displays, so I will investigate that way. In fact, now that I'm thinking,
the board is very close to the plastic itself on the edges (1~2mm) and there
are some traces going near the edge...

Well, I'll take a look at that and will post any conclusion I encounter.

Thanks again to all.

Mauricio Jancic
Janso Desarrollos - Microchip Consultants Program Member
KILLspaminfoKILLspamspamjanso.com.ar
http://www.janso.com.ar
(54) 11 - 4542 - 3519

2005\04\27@201752 by Dave VanHorn

flavicon
face
At 04:23 PM 4/27/2005, RemoveMERichard.ProsserTakeThisOuTspamPowerware.com wrote:

>Where can I get these "special" shoes from? They sound like a "must have"
>for trade shows.

Cheap plastic soled dress shoes.  I measured an inch spark, nice and fat.
Brand name, VanDeGraff, I think :)


2005\04\28@062731 by Joe McCauley

picon face
Do these same units fail again? Do replacement units in the same location
fail? Many years ago I had an 8051 based unit operate fine for several
months only to crash repetedly when the system was moved. Turned out people
had to cross a nylon carpet after the machine was moved to reach the system.
Static protection on input lines solved my problem then.

Joe

-----Original Message-----
From: spamBeGonepiclist-bouncesspamBeGonespammit.edu [TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu] On Behalf Of
Mauricio Jancic
Sent: 27 April 2005 15:53
To: 'Microcontroller discussion list - Public.'
Subject: RE: [PIC] STATIC anoyances..(?)


       
       My question was because some of the feeders (1 out of 40~50) stops
working and in most cases the problem is the DS1307 that is damaged. If I
replace it, everything is up and working again.



2005\04\28@083144 by Howard Winter

face
flavicon
picon face
Dave,

On Wed, 27 Apr 2005 19:18:07 -0500, Dave VanHorn wrote:

> At 04:23 PM 4/27/2005, RemoveMERichard.ProsserspamTakeThisOuTPowerware.com wrote:
>
> >Where can I get these "special" shoes from? They sound like a "must have"
> >for trade shows.
>
> Cheap plastic soled dress shoes.  I measured an inch spark, nice and fat.
> Brand name, VanDeGraff, I think :)

ROFL!  And for anyone else doing this test, if you use something conductive to make the spark, rather than
your finger, it's a lot less painful!  For example hold an all-metal key firmly between thumb and finger, and
advance the pointy end of it towards the other side.  If you're making good contact with it, you may feel
nothing, or just a tingle, instead of the nasty zap...

Cheers,


Howard Winter
St.Albans, England


2005\04\28@132733 by Dave VanHorn

flavicon
face
At 12:06 PM 4/27/2005, David Minkler wrote:
>Mauricio,
>
>Perhaps you could integrate a small piece of indium tin oxide coated
>film as the window to your display and use conductive sprays elsewhere.
>I just Googled on < +"indium tin oxide" +film > and had a fair
>number of hits.  I know that the people who manufacture display
>overlays for us (essentially a fancy label) use these kinds of films
>on some of our products.



When we solved our static problems, we ended up using none of these
sorts of things.
They are all rather expensive patches for poor designs.



2005\04\28@142820 by Mark Rages

face picon face
On 4/28/05, Howard Winter <HDRWEraseMEspam.....h2org.demon.co.uk> wrote:
> Dave,
>
> On Wed, 27 Apr 2005 19:18:07 -0500, Dave VanHorn wrote:
>
> > At 04:23 PM 4/27/2005, EraseMERichard.ProsserspamPowerware.com wrote:
> >
> > >Where can I get these "special" shoes from? They sound like a "must have"
> > >for trade shows.
> >
> > Cheap plastic soled dress shoes.  I measured an inch spark, nice and fat.
> > Brand name, VanDeGraff, I think :)
>
> ROFL!  And for anyone else doing this test, if you use something conductive to make the spark, rather than
> your finger, it's a lot less painful!  For example hold an all-metal key firmly between thumb and finger, and
> advance the pointy end of it towards the other side.  If you're making good contact with it, you may feel
> nothing, or just a tingle, instead of the nasty zap...
>

On the other hand, if you want it to hurt worse, put your finger on
one side of a flourescent tube and touch the other side to ground.  Do
this in the dark for the greatest effect.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

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