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'[EE] Current Probe?'
2010\03\23@125555 by Harold Hallikainen

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A tech just came to me with a problem on a board. A PIC is TRYING to drive
a line to 3.3V, but it's only getting to 1.9V. So, something somewhere is
holding it down. Has anyone had any luck with Hall effect current probes
in tracing where current is going on a board? What particular probe are
you using?

THANKS!

Harold



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2010\03\23@131734 by Mark Rages

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On Tue, Mar 23, 2010 at 12:20 PM, Harold Hallikainen
<spam_OUTharoldTakeThisOuTspamhallikainen.org> wrote:
> A tech just came to me with a problem on a board. A PIC is TRYING to drive
> a line to 3.3V, but it's only getting to 1.9V. So, something somewhere is
> holding it down. Has anyone had any luck with Hall effect current probes
> in tracing where current is going on a board? What particular probe are
> you using?
>

That's quite a bit of current.  The PIC has output resistance of ~35
ohms IIRC, so maybe 50 mA?  You should be able to find the current
sink with a good voltmeter.  To increase the resolution, measure from
the PIC pin to other places on the node in microvolt range.  Largest
drop is the winner.

Never used a hall effect current probe.

Regards,
Mark
markrages@gmail
--
Mark Rages, Engineer
Midwest Telecine LLC
.....markragesKILLspamspam@spam@midwesttelecine.com

2010\03\23@133039 by Marcel Duchamp

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On 3/23/2010 10:17 AM, Mark Rages wrote:
>
> That's quite a bit of current.  The PIC has output resistance of ~35
> ohms IIRC, so maybe 50 mA?  You should be able to find the current
> sink with a good voltmeter.  To increase the resolution, measure from
> the PIC pin to other places on the node in microvolt range.  Largest
> drop is the winner.

I'll second Marks comment of using a voltmeter.  That has worked well
for me for finding short circuits.  It helps to have access to a 5 or 6
digit system meter...

2010\03\23@133656 by Alan B Pearce

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> What particular probe are you using?

The old HP current trace probe that came in the logic probe set seemed to
work OK for this.

failing that working your way around the possible source locations with a 4
1/2 or more digit DVM also works well, looking for the highest voltage, as
that will be where the problem is.

2010\03\23@171822 by Dwayne Reid
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I have an old HP current probe that works well for this.  Just make
sure the little white dot is pointed in the direction that the trace
is running in.  I find that the probe works best with high-current
pulses best, although it will trace a DC current.  The little
thumb-wheel pot on the side of the probe sets the sensitivity.

I also (years ago) purchased something called a "Leak Seeker" that is
specifically designed for this kind of trouble-shooting.  It is
essentially a high-resolution DC voltmeter that controls the pitch of
a tone.  Its really cool in that it auto-zeros itself as you progress
along the trace(s) heading in the direction of the short.

You don't need to watch a meter - just listen to the tone as you move
the needle-point probe from place to place along the trace.  The
fine-tip needle easily penetrates the solder mask.

Its actually worked really, really well the several times that I've
used it.  Do note that its designed to locate DC faults (as opposed to pulses).

dwayne


At 11:20 AM 3/23/2010, Harold Hallikainen wrote:
{Quote hidden}

--
Dwayne Reid   <dwaynerspamKILLspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2010\03\23@190734 by Vitaliy

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Dwayne Reid wrote:
> I also (years ago) purchased something called a "Leak Seeker" that is
> specifically designed for this kind of trouble-shooting.  It is
> essentially a high-resolution DC voltmeter that controls the pitch of
> a tone.  Its really cool in that it auto-zeros itself as you progress
> along the trace(s) heading in the direction of the short.
>
> You don't need to watch a meter - just listen to the tone as you move
> the needle-point probe from place to place along the trace.  The
> fine-tip needle easily penetrates the solder mask.
>
> Its actually worked really, really well the several times that I've
> used it.  Do note that its designed to locate DC faults (as opposed to
> pulses).

Are these devices available nowadays? Anybody got a model number?

Vitaliy

2010\03\23@193112 by Marcel Duchamp

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On 3/23/2010 4:07 PM, Vitaliy wrote:
> Dwayne Reid wrote:
>> I also (years ago) purchased something called a "Leak Seeker" that is
>> specifically designed for this kind of trouble-shooting.  It is
>> essentially a high-resolution DC voltmeter that controls the pitch of
>> a tone.  Its really cool in that it auto-zeros itself as you progress
>> along the trace(s) heading in the direction of the short.
>>
>> You don't need to watch a meter - just listen to the tone as you move
>> the needle-point probe from place to place along the trace.  The
>> fine-tip needle easily penetrates the solder mask.
>>
>> Its actually worked really, really well the several times that I've
>> used it.  Do note that its designed to locate DC faults (as opposed to
>> pulses).
>
> Are these devices available nowadays? Anybody got a model number?
>
> Vitaliy
>
Maybe it's this one:
http://www.eds-inc.com/eds82.html

2010\03\23@212412 by Lucas Thompson

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I still use an old Wavetek handheld dmm that has that same kind of
reading-to-audio-tone function for finding shorts and intermittent
connections. It's really handy and a shame that all meters don't have
this same thing.

On 3/23/10, Vitaliy <.....piclistKILLspamspam.....maksimov.org> wrote:
{Quote hidden}

> -

2010\03\23@222245 by YES NOPE9

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{Quote hidden}

Does anyone have a block diagram of the ( voltage ? ) reading-to-audio-
tone electronics ?
Gus

2010\03\24@023052 by Russell McMahon

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> Does anyone have a block diagram of the ( voltage ? )
> reading-to-audio-tone electronics ?

Taking that almost unbelievable question at face value.

1. Draw rectangle

Label rectangle "VCO"
Add input - label Vin.
Add output - label Fout
QED.

or

2. Use CD4046 block diagram.
Essentially as above with a few support components thrown in to set
frequency per Volt etc.

http://focus.ti.com/lit/ds/symlink/cd4046b.pdf

3. For extra points add a simple differential amplifier which amplifies the
small voltage beteen its probes to a level that best suits the 4046.


  Russell

2010\03\24@050332 by Russell McMahon

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> > Does anyone have a block diagram of the ( voltage ? )
> > reading-to-audio-tone electronics ?

> 2. Use CD4046 block diagram.
> Essentially as above with a few support components thrown in to set frequency per Volt etc.
>
> http://focus.ti.com/lit/ds/symlink/cd4046b.pdf

This may work better.
The other tends to crash on loading.
May just not like being readf uiopside down.

   http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/CD4046BC.pdf



R

2010\03\24@144611 by Michael Rigby-Jones

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> -----Original Message-----
> From: piclist-bouncesspamspam_OUTMIT.EDU [@spam@piclist-bouncesKILLspamspamMIT.EDU] On
Behalf
> Of Mark Rages
> Sent: 23 March 2010 17:18
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Current Probe?
>
> On Tue, Mar 23, 2010 at 12:20 PM, Harold Hallikainen
> <KILLspamharoldKILLspamspamhallikainen.org> wrote:
> > A tech just came to me with a problem on a board. A PIC is TRYING to
> drive
> > a line to 3.3V, but it's only getting to 1.9V. So, something
somewhere
> is
> > holding it down. Has anyone had any luck with Hall effect current
probes
> > in tracing where current is going on a board? What particular probe
are
> > you using?
> >
>
> That's quite a bit of current.  The PIC has output resistance of ~35
> ohms IIRC, so maybe 50 mA

It depends on the particular PIC being used, but they are typically a
lot weaker sourcing current with a 3v supply than 5v.  The 12F617 I have
been using recently shows an equivalent output resistance of ~150 Ohms
at 25 degrees Celsius with a 3v supply and small currents (< 4.0mA), and
somewhat more than double that at 125 degrees Celsius.

Regards

Mike

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