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'[PIC]: Noise on Vcc causes PIC to Reset???'
2002\01\10@175357 by WEBB,TIM (A-Sonoma,ex1)

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This may seem like a stupid question but why does my PIC reset from noise on
Vcc?

The noise is generated by the flip of a switch that connects or disconnects
Vcc to a 74VHC125, NC7S14, & 93C86.
I have .1uf caps across the power supply at each chip including the PIC.

The MCLR is tied to Vcc with a 1K ohm resistor.

I don't have a oscope handy to look at the Vcc line right now.

Am I missing something...

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2002\01\10@181311 by Dave Dilatush

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Tim Webb wrote...

>This may seem like a stupid question but why does my PIC reset from noise on
>Vcc?
>
>The noise is generated by the flip of a switch that connects or disconnects
>Vcc to a 74VHC125, NC7S14, & 93C86.
>I have .1uf caps across the power supply at each chip including the PIC.
>
>The MCLR is tied to Vcc with a 1K ohm resistor.
>
>I don't have a oscope handy to look at the Vcc line right now.
>
>Am I missing something...

I think your reset might be caused by the very brief (but deep) droop in
Vcc that occurs when the 0.1uF bypass capacitors are first connected
across Vcc when the switch is flipped.  Even a brief droop in Vcc can
cause the PIC to get upset.

You might try adding more bypass capacitance directly across the PIC; a
10uF tantalum might be a good starting point and if it does the trick,
you can then start trying smaller values if you want.

Dave Dilatush

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2002\01\10@183146 by dave vanhorn

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At 03:49 PM 1/10/2002 -0700, WEBB,TIM (A-Sonoma,ex1) wrote:
>This may seem like a stupid question but why does my PIC reset from noise on
>Vcc?
>
>The noise is generated by the flip of a switch that connects or disconnects
>Vcc to a 74VHC125, NC7S14, & 93C86.
>I have .1uf caps across the power supply at each chip including the PIC.

Likely you are glitching VCC when the switch closes.
This is a pretty un-standard thing to do.

One fix would be just a little series resistance in the line. 1 ohm might
be enough.
The idea is to make all those discharged caps not be such a good
short-circuit at power-on.
Another idea that comes to mind, is to use a softer switch, like a
transistor, which will go through a linear region before saturating on.

Another badness, when VCC crashes, your cap on MCLR is likely to discharge
through the chip's protection diodes, which is not good. You may blow the
chip, or you may see no effect.

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2002\01\11@025622 by Vasile Surducan

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On Thu, 10 Jan 2002, dave vanhorn wrote:

> One fix would be just a little series resistance in the line. 1 ohm might
> be enough.
> The idea is to make all those discharged caps not be such a good
> short-circuit at power-on.

 Dave, ufortunately this trick is not working all the time. Sometime
instead of minimising glitch is increasing the noise on supply tracks. I
not recommend this solution for analogic board and mixed signal board. I
can't explain why, is just a remark based on practical experience ( I
have tested the method with resistors from 1 to 10 ohm on different boards
)
regards, Vasile

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2002\01\11@080122 by Drew Vassallo

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>This may seem like a stupid question but why does my PIC reset from noise
>on
>Vcc?

In your specific case, as others have pointed out, your reset may not in
fact be due directly to the "noise" generated by the switch, but rather the
drop in Vcc.

However, I have had applications where noise from servos or motors caused
very bad reset conditions when the battery supply dropped to ~5.1 VDC.
Worked fine with the source at >5.1 VDC, but once the battery dropped, I had
major problems.  To make matters worse, different PICs would behave
differently, even among those from the same series (i.e. 16C71 worked 100%
better in the same application than the 16C711 did).  I never did get that
problem figured out, though I haven't done much testing on cleaning up the
noise on the servo lines.  If you find a good solution, please post it; I'd
be interested.

--Andrew


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2002\01\11@083820 by dave vanhorn

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At 09:45 AM 1/11/2002 +0200, Vasile Surducan wrote:
>On Thu, 10 Jan 2002, dave vanhorn wrote:
>
> > One fix would be just a little series resistance in the line. 1 ohm might
> > be enough.
> > The idea is to make all those discharged caps not be such a good
> > short-circuit at power-on.
>
>   Dave, ufortunately this trick is not working all the time. Sometime
>instead of minimising glitch is increasing the noise on supply tracks. I
>not recommend this solution for analogic board and mixed signal board. I
>can't explain why, is just a remark based on practical experience ( I
>have tested the method with resistors from 1 to 10 ohm on different boards


As I said, this whole approach of connecting a discharged capacitance to a
regulated supply line is highly inadvisable.
The series R would greatly depend on the load.  When I design a section to
be powered down, it gets it's own regulator, running from the unreg supply.
Then none of this mess is a problem..

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2002\01\11@121446 by Dave Dilatush

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Drew Vassallo wrote...

>...I have had applications where noise from servos or motors caused
>very bad reset conditions when the battery supply dropped to ~5.1 VDC.
>Worked fine with the source at >5.1 VDC, but once the battery dropped, I had
>major problems.  To make matters worse, different PICs would behave
>differently, even among those from the same series (i.e. 16C71 worked 100%
>better in the same application than the 16C711 did).  I never did get that
>problem figured out, though I haven't done much testing on cleaning up the
>noise on the servo lines.  If you find a good solution, please post it; I'd
>be interested.

One entire area of design that's often overlooked, especially when
breadboarding, is grounding topology.  I've run into trouble in the past
when, despite what I thought was careful Vcc/Gnd bypassing of every
chip, I didn't pay enough attention to where currents--especially large,
switched currents--were flowing.  The large dI/dT caused by a
sharp-edged signal returning through the ground system to its source can
generate transient voltages that cause major problems if the ground
system isn't planned carefully.

I absolutely HATE grounding-related problems; they're by far the most
difficult to debug of all the kinds of problems I've seen, and I've
found that it's well worth the trouble of being absolutely anal about
ground system design, just to be rid of these problems entirely.

Dave

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2002\01\11@124821 by dave vanhorn

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>
>I absolutely HATE grounding-related problems; they're by far the most
>difficult to debug of all the kinds of problems I've seen, and I've
>found that it's well worth the trouble of being absolutely anal about
>ground system design, just to be rid of these problems entirely.
>
>Dave


I largely agree.
Debugging time takes away from development time, so I try not to do much of
that.
Hobby time is too precious to waste as well.

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2002\01\11@155336 by Tim McDonough

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>One entire area of design that's often overlooked, especially when
>breadboarding, is grounding topology.  I've run into trouble in the
past
>when, despite what I thought was careful Vcc/Gnd bypassing of every
>chip, I didn't pay enough attention to where currents--especially
large,
>switched currents--were flowing.  The large dI/dT caused by a
>sharp-edged signal returning through the ground system to its source
can
>generate transient voltages that cause major problems if the ground
>system isn't planned carefully.

Grounding is especially tough when a solderless breadboard is being
used. I've seen prople who struggle getting stuff to work on them
because they ignore every rule imagineable: wimpy grounds, bypass caps
nowhere near the IC's, unused pins left floating, long wires
(antennas!) snaking all over the place...

Tim

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2002\01\11@162410 by Dave Dilatush

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Tim McDonough <spamBeGonetimspamBeGonespammcdonough.net> wrote...

>Grounding is especially tough when a solderless breadboard is being
>used. I've seen prople who struggle getting stuff to work on them
>because they ignore every rule imagineable: wimpy grounds, bypass caps
>nowhere near the IC's, unused pins left floating, long wires
>(antennas!) snaking all over the place...

I used to use those things until I decided that, whatever their value in
terms of convenience, their flaws were causing me more work--in the form
of debugging--than they were saving.

Nearly all of my breadboarding work anymore is done on 0.1" perfboard
with wire-wrap sockets for the ICs and T-44 pins for the discretes, and
using AWG14 or AWG16 busbar for the grounds, either gridded (for
digital) or in a star topology (for analog).  Using this method I find I
can build stuff almost as fast as I could with the solderless
breadboards, and end up with far fewer headaches and, in the end, less
time wasted.

Another factor is that in my hobby stuff I like to work on a large
number of projects at once, sometimes a dozen or more; and those
solderless breadboards aren't cheap.

Dave Dilatush

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2002\01\11@225026 by Karl Seibert

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If you are interested in picking one up relatively cheaply,
check http://www.mcmelectronics.com item number 72-345 .
$12.23 for a 2390 hole breadboard.  I don't know what the
minimum order or shipping is there (I work 0.5 miles from
the warehouse and can hit the will call window).  Make sure
that you use the web to order because sometimes the price
on the phone or catalog doesn't match the web price.

Karl

Quoting Dave Dilatush <RemoveMEdilatushspamTakeThisOuTHOME.COM>:
> Another factor is that in my hobby stuff I like to work on a large
> number of projects at once, sometimes a dozen or more; and those
> solderless breadboards aren't cheap.
>

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2002\01\12@034423 by Steve Faulkner

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I've done wire-wrap in the past... but what are T-44 pins?

----- Original Message -----
From: "Dave Dilatush" <EraseMEdilatushspamHOME.COM>
To: <RemoveMEPICLISTEraseMEspamEraseMEMITVMA.MIT.EDU>
Sent: Friday, January 11, 2002 1:22 PM
Subject: Re: [PIC]: Noise on Vcc causes PIC to Reset???


Tim McDonough <RemoveMEtimspam_OUTspamKILLspammcdonough.net> wrote...

>Grounding is especially tough when a solderless breadboard is being
>used. I've seen prople who struggle getting stuff to work on them
>because they ignore every rule imagineable: wimpy grounds, bypass caps
>nowhere near the IC's, unused pins left floating, long wires
>(antennas!) snaking all over the place...

I used to use those things until I decided that, whatever their value in
terms of convenience, their flaws were causing me more work--in the form
of debugging--than they were saving.

Nearly all of my breadboarding work anymore is done on 0.1" perfboard
with wire-wrap sockets for the ICs and T-44 pins for the discretes, and
using AWG14 or AWG16 busbar for the grounds, either gridded (for
digital) or in a star topology (for analog).  Using this method I find I
can build stuff almost as fast as I could with the solderless
breadboards, and end up with far fewer headaches and, in the end, less
time wasted.

Another factor is that in my hobby stuff I like to work on a large
number of projects at once, sometimes a dozen or more; and those
solderless breadboards aren't cheap.

Dave Dilatush

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2002\01\12@091802 by Dave Dilatush

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Steve,

These are wire-wrap pins for mounting resistors, capacitors, diodes and
the like; see Vector Electronics catalog page at:

http://www.vectorelect.com/img/Web-Pdf/Access-Terminals-Pins.PDF

There are also the T68 pins for components with larger leads.

I insert the pins using Vector's insertion tool, then "seat" the pins
all the way into the board by pressing down with a medium-hot soldering
iron.  Then I solder the component leads to the pins.  Makes for a nice,
solid breadboard and is pretty quick.

Dave

Steve Faulkner <EraseMEStevespamspamspamBeGoneFAULKNER.NET> wrote...

>I've done wire-wrap in the past... but what are T-44 pins?
>
>{Original Message removed}

2002\01\12@093145 by Dave Dilatush

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Karl,

Thanks for the tip, but as I indicated in my post, I really don't use
those things anymore because of the signal-integrity problems they
create.

Thanks anyway, though.

Dave

Karl Seibert <RemoveMEkarlseibertKILLspamspamSISCOM.NET> wrote...

{Quote hidden}

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