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'[PIC]:Program jumps upon shaking'
2001\03\15@230208 by Andrew Scott

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Hi all,

My problem is that I have built a vero board application with a PIC, LCD
display and an acceleromter. The circuit produces the reading from the
acceleromter onto the LCD display. When I shake the vero board hard the PIC
seems to "jump" to another part of the program as if an interrupt occured.
The program will loop through an incorrect part of the program. My memory
paging jumps (PClath) seem to be fine. The circuit must be able to withstand
this force.

I have produced two vero board projects and it happens on both of those so I
dont think it is the connections. I have shaken the connections and shaken
the LCD display and it does not happen. It seems to only happen when the PIC
is shaken. If the accelerometer is removed from the circuit and the PIC is
shaken the problem still occurs.

Does anybody know if the PIC can only withstand a certian G force? I am
using a PIC16f877. Does microchip produce a chip that can withstand the
G-Force.

Or is it sonething that I have done in the code.

Kind Regards,

Andrew Scott

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2001\03\16@005641 by David VanHorn

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>
>Does anybody know if the PIC can only withstand a certian G force? I am
>using a PIC16f877. Does microchip produce a chip that can withstand the
>G-Force.

The pic will outlive you by a good bit.
Look elsewhere.

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2001\03\16@065515 by mike

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On Fri, 16 Mar 2001 00:57:27 -0500, you wrote:

>>
>>Does anybody know if the PIC can only withstand a certian G force? I am
>>using a PIC16f877. Does microchip produce a chip that can withstand the
>>G-Force.
>
>The pic will outlive you by a good bit.
>Look elsewhere.
The crystal will probably be the first thing to snap, not the PIC.

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2001\03\16@075022 by Thomas McGahee

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Is the PIC soldered in place or in a socket? If it is socketed
then your problem with G forces may be that one or more PIC
pins are sliding in the socket and intermittent. Directly
soldering in the components will eliminate this sort of problem.

Note: ANY item not soldered in place could be the problem.

Fr. Tom McGahee

{Original Message removed}

2001\03\16@082427 by Eisermann, Phil [Ridg/CO]

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Well, I did a little HALT testing on a board with a PIC in it. HALT = Highly
Accelerated Life Test. One of the tests was a 6-axis random vibration test.
The rms value of the G-force on the board was 20g-25g when the transformer
failed. The PIC and crystal survived around 35g before strange things
started happening. The PIC was a 16C711, the crystal a 4MHz through hole. I
have performed a similar test on an ADuC812 with a 11.0592MHz SMD crystal,
and again strange things started happening around 35g. So, it is unlikely to
be the crystal, either.

But, have you considered ESD? when you shake the board by hand, you will be
electrically charging yourself. The voltage will be high enough that the
potential can jump an air gap. I'm going to guess that you're seeing an
ESD-related event. Try protecting the inputs by inserting a series resistor,
decoupling capacitor, and a zener diode. Also make liberal use of decoupling
capacitors throughout the board.


{Original Message removed}

2001\03\16@085357 by Roman Black

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Eisermann, Phil [Ridg/CO] wrote:
>
> Well, I did a little HALT testing on a board with a PIC in it. HALT = Highly
> Accelerated Life Test. One of the tests was a 6-axis random vibration test.
> The rms value of the G-force on the board was 20g-25g when the transformer
> failed. The PIC and crystal survived around 35g before strange things
> started happening. The PIC was a 16C711, the crystal a 4MHz through hole. I
> have performed a similar test on an ADuC812 with a 11.0592MHz SMD crystal,
> and again strange things started happening around 35g. So, it is unlikely to
> be the crystal, either.
>
> But, have you considered ESD? when you shake the board by hand, you will be
> electrically charging yourself. The voltage will be high enough that the
> potential can jump an air gap. I'm going to guess that you're seeing an
> ESD-related event. Try protecting the inputs by inserting a series resistor,
> decoupling capacitor, and a zener diode. Also make liberal use of decoupling
> capacitors throughout the board.


Great point, esd or even hand capacitance and the
PIC osc. Also, when finding dry joints in appliances
they are usually VERY movement sensitive. Using
veroboard can often give bad joints, I scrub mine
with abrasive before soldering. It's usually non-tinned
and gets corroded easily.
-Roman

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2001\03\16@124939 by Alan B. Pearce

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>The rms value of the G-force on the board was 20g-25g when the transformer
>failed. The PIC and crystal survived around 35g before strange things
>started happening. The PIC was a 16C711, the crystal a 4MHz through hole. I
>have performed a similar test on an ADuC812 with a 11.0592MHz SMD crystal,
>and again strange things started happening around 35g. So, it is unlikely to
>be the crystal, either.

Good grief - what are you doing with these things. The item I am working on for
a satellite is tested to 9G and for that we stake, glue tie and bolt everything
in sight to allow for mechanical Q effects, and your going to around 4 times
this without a single dob of goo on any components?

I wonder what your expecting to use it in that you test it to these sort of
accelerations.

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2001\03\16@130404 by Dale Botkin

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On Fri, 16 Mar 2001, Alan B. Pearce wrote:

> >The rms value of the G-force on the board was 20g-25g when the transformer
> >failed. The PIC and crystal survived around 35g before strange things
> >started happening. The PIC was a 16C711, the crystal a 4MHz through hole. I
> >have performed a similar test on an ADuC812 with a 11.0592MHz SMD crystal,
> >and again strange things started happening around 35g. So, it is unlikely to
> >be the crystal, either.
>
> Good grief - what are you doing with these things. The item I am working on for
> a satellite is tested to 9G and for that we stake, glue tie and bolt everything
> in sight to allow for mechanical Q effects, and your going to around 4 times
> this without a single dob of goo on any components?
>
> I wonder what your expecting to use it in that you test it to these sort of
> accelerations.

Artillery comes to mind...

Dale
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2001\03\16@134056 by Barry Gershenfeld

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>Eisermann, Phil [Ridg/CO] wrote:
>> But, have you considered ESD? when you shake the board by hand, you will be
>> electrically charging yourself. The voltage will be high enough that the
>> potential can jump an air gap.

R:o)man wrote:
>Great point, esd or even hand capacitance and the
>PIC osc. Also, when finding dry joints in appliances
>they are usually VERY movement sensitive.


I'll add my favorite: Floating inputs.  As a matter of fact
I have one of those MPLAB ICD boards from Advanced Transdata,
and with a PIC programmed for ICD (which inserts a debug
monitor into the code) but not connected to the ICD, it should
sit there and do nothing because the code waits for messages
from MPLAB. But if I wave it around or set it near my monitor
I can get it to jump into the application code and run at various
apparent speeds.

The high impedance combined with just a few pf of capacitance
on a floating IC pin can keep it in one state or another for
many seconds.

Barry

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2001\03\16@135757 by Eisermann, Phil [Ridg/CO]

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       *grin* I usually get that sort of reaction :)

       To clarify my sanity: No, I don't expect our boards to last
continuously under 30g. I don't even expect them to see 30g in the field. A
HALT test is designed to break the board. There is really no such thing as
'passing' a HALT test. If nothing breaks, you're doing the test wrong.

       The object is to find weak points in the board, fix them, and
continue to apply higher stress levels. The theory is based on PoF (Physics
of Failure). WRT to the HALT test, PoF basically says that the higher the
applied stress, the faster the unit will fail. With these kinds of stresses,
you will *not* be able to estimate MTBF. But you *will* stimulate failures
that would occur in the field. Specifically, the failure modes precipitated
by these stresses are the same ones seen after years in the field. The
difference is, with a robust circuit, running a life test until something
fails can take many months. With HALT, it only takes a few hours (including
setup time). A modified version of HALT can be used for production screening
to weed out infant mortalities much faster and more effectively than
burn-in. But you or your contract manufacturer has to have a special chamber
on site, and they run $100K to $150K, not including the cost of running LN
lines (and thats about $100.00 per foot, and an OSHA headache)

       Anyway, the idea is that, by finding the weak points and improving
them, you end up with a more robust product. It's really a very enlightening
sort of test. Especially if the board frosts over, capacitors start flying
off, or bent transistor leads start breaking. That was particularly
eye-opening. One time, the contract mfg. had damaged the leads during the
forming process. Wouldn't have found that without this test until after
stuff started coming back.

       For reference, these tests were performed at the Accelerated
Reliability Test Center (division of QualMark) near Detroit. They do most of
their business with the automobile industry. The kinds of stresses we are
talking about are indeed huge. We cycled the boards from -80C to +90C (thats
-112F to +194F) in about 90 seconds!, with a 10 minute dwell time at each
end. Then came the 6-axis random vibration. It's basically a table with
pneumatic hammers on the bottom. Accelerometers measure the vibration from
2Hz to 10kHz, the controller computes the rms value at 2kHz, and adjusts as
necessary. Then we combined the temperature cycling with vibration. BTW, the
boards were powered the whole time.

{Original Message removed}

2001\03\17@071326 by Peter L. Peres

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>Artillery comes to mind...

You can reach and exceed 35G in a tennis or golf ball, football, anything
that is hit with a hammer or a bat, anything that falls down from more
than about 2 meters height (assuming some cushioning). Model aircraft,
cars, moving parts in machinery, collision between cars, even electric
cars in a kid playing ground, etc.

Peter

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2001\03\18@233310 by Dave Bell

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Phil Eisermann, <KILLspampeisermaKILLspamspamRIDGID.COM>, wrote:

>A HALT test is designed to break the board. There is really no such thing
>as 'passing' a HALT test. If nothing breaks, you're doing the test wrong.

>Anyway, the idea is that, by finding the weak points and improving them,
>you end up with a more robust product.

   I believe this is the reverse in many ways, of the long term "testing"
supposedly run by Henry Ford. He was reported to have sent his engineers
to junkyards, to collect part from high-mileage Ford cars. They were
carefully analyzed, and any parts showing less than average wear, compared
to other parts, were candidates for redesign, as they were obviously too
robust!

Dave

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2001\03\19@003600 by David VanHorn

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At 12:55 PM 3/16/01 -0600, Eisermann, Phil [Ridg/CO] wrote:
>         *grin* I usually get that sort of reaction :)
>
>         To clarify my sanity: No, I don't expect our boards to last
>continuously under 30g. I don't even expect them to see 30g in the field. A
>HALT test is designed to break the board. There is really no such thing as
>'passing' a HALT test. If nothing breaks, you're doing the test wrong.

I agree with your approach, up to a point.
It sounds to me like your crystal is crashing into the sides of the can.
Check the specs, but I doubt it's rated for that sort of abuse.

And therein is the fault I see in this method.
You're getting into areas where you're exciting threshold effects, not
wearout effects.
You'll be seeing fatigue failure in things that would NEVER fail in real
life, because they wouldn't get stressed that hard, much less repetitively.

Don't get me wrong, it has it's uses.  I used to test new packing by
kicking a carton of terminals off the third floor loading dock.  It didn't
take long to set up, and it was a pretty good indicator of how well the
packing would hold up.

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2001\03\19@081340 by Olin Lathrop

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> Don't get me wrong, it has it's uses.  I used to test new packing by
> kicking a carton of terminals off the third floor loading dock.  It didn't
> take long to set up, and it was a pretty good indicator of how well the
> packing would hold up.

You must have some very tall trucks!


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2001\03\19@082545 by David VanHorn

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At 07:54 AM 3/19/01 -0500, Olin Lathrop wrote:
> > Don't get me wrong, it has it's uses.  I used to test new packing by
> > kicking a carton of terminals off the third floor loading dock.  It didn't
> > take long to set up, and it was a pretty good indicator of how well the
> > packing would hold up.
>
>You must have some very tall trucks!

That was the biggest stress I could see them getting in real life.
It was an unusual factory I guess, but assembly finished off on the 3rd
floor, and product in cases went down on an elevator to the truck bay.


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2001\03\19@090656 by Eisermann, Phil [Ridg/CO]

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David VanHorn wrote:

"I agree with your approach, up to a point.
It sounds to me like your crystal is crashing into the sides of the can.
Check the specs, but I doubt it's rated for that sort of abuse.

And therein is the fault I see in this method.
You're getting into areas where you're exciting threshold effects, not
wearout effects."

well, yes but no.

No, because what you are doing with this sort of test is, in effect, time
compression. So we expect that crystal to fail. We're just getting it to
fail sooner. There's nothing wrong with taking this test way beyond the
individual component's specs. We are, after all, trying to break it. We're
trying to make the product as a whole more robust.

Yes, because you are right. Taking it beyond what it can possibly survive
will cause it fail, and  under normal conditions that failure mode might not
ever be seen. You do need to apply some common sense. There are physical
limitations, and I do realize that. But, if the crystal is the first thing
that fails in your HALT test, it's a pretty good bet that field failures
will also show a failed crystal. Whether or not that came about due to
vibration. Of course, if vibration is the only thing that causes the crystal
to fail, then yeah, the excess stress in the test is not really valid.

But we don't make delicate lab instruments. We make plumbing tools.
Construction crews drop tools all the time (from ladders, of course). The
tools get wet. They get extremely muddy and dusty. They are left in the back
of a truck in the middle of winter, then taken inside a heated building. Or
they are left in the truck in the middle of summer, and get taken inside an
air conditioned building. All of these stresses add up over time and shorten
the life. Again, we're after time compression. Get them to fail early so you
understand how they fail, and fix it before it ever gets to a customer.

Perhaps you will see a way to cushion the crystal, or even the whole
assembly. Perhaps you choose a different crystal, or switch to an RC if
timing is not critical. And by taking the crystal beyond its specs, you will
likely encounter something else that breaks. Of course, it does not always
make sense to ruggedize a product beyond a point. If the improvement is
relatively expensive, and only yields a small improvement, then perhaps it
is not worth it.

Then there's the company 'attitude' to consider. For the computer industry,
where they want us to buy a new PC every 6 months, this sort of thing
probably does not. But, for someone like my company, whose (newly adopted)
motto is "Tools engineered for maximum uptime" and who offers a life-time
warranty on tools, it makes a lot of sense. Of course, our price reflects
that :) We have always been known for robust products. There's a lot of our
machines made in the late sixties and early seventies that we still service.
Now that we're integrating electronics, we needed a way to get there. Still
learning, but have come a long way.

Ok, now we have drifted sufficiently off the topic of the original question
:) If we continue this discussion, we should probably mark it [OT].

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2001\03\19@100608 by David VanHorn

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>
>Yes, because you are right. Taking it beyond what it can possibly survive
>will cause it fail, and  under normal conditions that failure mode might not
>ever be seen. You do need to apply some common sense. There are physical
>limitations, and I do realize that. But, if the crystal is the first thing
>that fails in your HALT test, it's a pretty good bet that field failures
>will also show a failed crystal. Whether or not that came about due to
>vibration. Of course, if vibration is the only thing that causes the crystal
>to fail, then yeah, the excess stress in the test is not really valid.


Case in point.
The crystal's most likely failure mode in this case is actually slamming
into the case walls internally.
This isn't something that's going to happen a little at a lower acceleration.
It won't happen at ALL until you exceed a threshold acceleration.
If the part won't take the stresses it's going to get in the field, then
spec a different part, or protect it from the stresses, but don't take a
part rated for X, and expect it to withstand 2X for half the time (or even
any time with some parts)

>But we don't make delicate lab instruments. We make plumbing tools.
>Construction crews drop tools all the time (from ladders, of course). The
>tools get wet. They get extremely muddy and dusty. They are left in the back
>of a truck in the middle of winter, then taken inside a heated building. Or
>they are left in the truck in the middle of summer, and get taken inside an
>air conditioned building. All of these stresses add up over time and shorten
>the life. Again, we're after time compression. Get them to fail early so you
>understand how they fail, and fix it before it ever gets to a customer.

We had a lot of the same stresses applied to credit card terminals. :)

Well.. Some of the stresses add up, some don't.
Let's take a glass display tube.  You either stress it to breaking, or you
don't.
You can stress it all you like below breaking, and nothing's going to
happen to it.

OTOH, socket pins, and bad solder joints fatigue out really well.


>Perhaps you will see a way to cushion the crystal, or even the whole
>assembly. Perhaps you choose a different crystal, or switch to an RC if
>timing is not critical. And by taking the crystal beyond its specs, you will
>likely encounter something else that breaks.


Again, to a point I agree with you, but then it becomes "well Duh!"
You have to be sure that these additional stresses are actually causing the
same failures that you see in the field. Otherwise, you're just building
extra cost into the product.



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