Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default A useful addition to your toolkit

https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series resistance
and you have a *very* cheap current probe for your scope.
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On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
wrote:

https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series resistance
and you have a *very* cheap current probe for your scope.


I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.

My real problem with current measurement is DC, on PC boards. We want
to know how much current, say, an FPGA is using. Sometimes I include
current shunts in a layout, but sometimes I don't.

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible. You
can measure millivolt and microvolt drops across traces and vias.




--

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lunatic fringe electronics

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On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


Indeed they're not. But your meter is presumably *only* designed for use
at 60Hz, I would imagine. Hook it up to a 100Hz signal and you'll see
nothing at all in all probability. ;-)

One can use existing switcher inductors as current shunts. I wish I had
a PCB trace current probe, but that's probably not posssible. You can
measure millivolt and microvolt drops across traces and vias.


Do they even exist? That would be amazing but no doubt *way* beyond what
I can justify to splash out on as a mere hobbyist.

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On Sun, 5 Mar 2017 16:18:50 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


Indeed they're not. But your meter is presumably *only* designed for use
at 60Hz, I would imagine. Hook it up to a 100Hz signal and you'll see
nothing at all in all probability. ;-)

One can use existing switcher inductors as current shunts. I wish I had
a PCB trace current probe, but that's probably not posssible. You can
measure millivolt and microvolt drops across traces and vias.


Do they even exist? That would be amazing but no doubt *way* beyond what
I can justify to splash out on as a mere hobbyist.



A 1" long, 20 mil wide 1oz trace will be about 25 milliohms. 1 amp
makes 25 millivolts, and lots of cheapish DVMs will resolve that well
enough. You probably need a bench DVM with microvolt resolution to
measure, say, 1 amp running through a via, but you could build a
little microvolt meter or amp pretty easily. PCB trace and via
resistances need to be calibrated, which is only a minor nuisance.

Here are some pcb-trace shunts, down near the connector:

https://dl.dropboxusercontent.com/u/...ower_Board.JPG

One of the great mysteries of electronics is "where is the current
going?" Sometimes a thermal imager helps figure that out. A little
magnetometer would be fun, not hard to do these days.




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lunatic fringe electronics

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Default A useful addition to your toolkit

On 05/03/2017 15:44, John Larkin wrote:
I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


Tell that to a condition monitoring engineer!




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They do make special current probes specifically for doing traces
on a PC board. without cutting traces or requiring a loop of wire.
http://www.power-mag.com/pdf/feature_pdf/1327592496_TTI_Layout_1.pdf


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On Sun, 5 Mar 2017 15:07:41 -0600, Foxs Mercantile
wrote:

They do make special current probes specifically for doing traces
on a PC board. without cutting traces or requiring a loop of wire.
http://www.power-mag.com/pdf/feature_pdf/1327592496_TTI_Layout_1.pdf


Looks expensive, and I'd guess not very accurate.


--

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lunatic fringe electronics

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On 3/5/2017 3:37 PM, John Larkin wrote:
Looks expensive, and I'd guess not very accurate.


http://www.aimtti.us/product-category/current-probes/aim-i-prober-520
It is expensive. At $795 for the basic probe.
Data sheet:
http://resources.aimtti.com/datasheets/prec-iprober520-5p.pdf
Instruction manual:
http://resources.aimtti.com/manuals/I-prober_Instruction_Manual-Iss5.pdf



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Foxs Mercantile wrote...

John Larkin wrote:
Looks expensive, and I'd guess not very accurate.


http://www.aimtti.us/product-category/current-probes/aim-i-prober-520
It is expensive. At $795 for the basic probe.
Data sheet:
http://resources.aimtti.com/datasheets/prec-iprober520-5p.pdf
Instruction manual:
http://resources.aimtti.com/manuals/I-prober_Instruction_Manual-Iss5.pdf


The expense we can handle, if, for example, it'll
give us adequate help in debugging our switching
power supply designs. But the calibrating scheme
for trace current measurements looks iffy. But
maybe along with other measurements, power in,
voltage and power out, etc., it could do the job.
It is fast enough to look at inductor currents.


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On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin
wrote:

On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
wrote:

https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series resistance
and you have a *very* cheap current probe for your scope.


I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.

My real problem with current measurement is DC, on PC boards. We want
to know how much current, say, an FPGA is using. Sometimes I include
current shunts in a layout, but sometimes I don't.


I generally use a ferrite (pi filter) on the supplies to uCs and DSPs
for EMI, then substitute a shunt to measure the power during test.

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible. You
can measure millivolt and microvolt drops across traces and vias.


The old HP current probe was a great debugging tool.
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John Larkin wrote:



I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


** Mains current waveforms are VERY interesting, but not if all you can see is 60Hz. A Hall effect transducer is needed to do the job properly.

The one is use is by LEM and has response to 100kHz, allows me to see currents as low as 1mA and up to 100A peak.


..... Phil
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On Sun, 05 Mar 2017 19:56:44 +0000, JM
wrote:

On 05/03/2017 15:44, John Larkin wrote:
I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


Tell that to a condition monitoring engineer!


I don't design AC power supplies any more. I can buy an entire nice
PFC switcher for less than I could buy a 60 Hz power transformer.
Since the supplies all come with UL/CE/VDE/etc stickers, I don't care
about their input current waveforms.


--

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lunatic fringe electronics

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On 3/5/2017 4:37 PM, John Larkin wrote:
On Sun, 5 Mar 2017 15:07:41 -0600, Foxs Mercantile
wrote:

They do make special current probes specifically for doing traces
on a PC board. without cutting traces or requiring a loop of wire.
http://www.power-mag.com/pdf/feature_pdf/1327592496_TTI_Layout_1.pdf


Looks expensive, and I'd guess not very accurate.


Seems to me it would be a *great* tool for finding where the currents
are going. I thought that would be a good thing?

--

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On 3/5/2017 11:58 PM, rickman wrote:

Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?


It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


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On 3/6/2017 1:56 AM, Foxs Mercantile wrote:
On 3/5/2017 11:58 PM, rickman wrote:

Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?


It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


You mean like thermal cameras?

--

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On 06/03/2017 00:41, wrote:
The old HP current probe was a great debugging tool.



+1 I'd love an HP-547A

piglet

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On Mon, 06 Mar 2017 00:56:56 -0600, Foxs Mercantile wrote:

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


For the *real* cheapskates out there, there's this alternative:

http://www.ebay.com/itm/100A-SCT-013...urrent-sensor-
Split-Core-Transformer-YH-/201842524936?
hash=item2efec08308:g:vm8AAOSwCGVX3BYF

Claims to be able to handle up to 100A!

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On Mon, 6 Mar 2017 00:56:56 -0600, Foxs Mercantile
wrote:

On 3/5/2017 11:58 PM, rickman wrote:

Seems to me it would be a *great* tool for finding where the
currents are going. I thought that would be a good thing?


It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


It's not hard to figure where current is going: just measure voltage
drops. What's sometimes difficult is quantifying it.

Just now we're laying out a 10-layer board with two ground planes and
three power planes. There are 22 power supplies. Most of the power
distribution will be interestingly-shaped interleaved pours, not
traces, on various layers.

That magnetic gadget would be hopelessly confused. Multiple currents
and various return paths would make it useless.

My favorite tool for tracing unusual current flows is my Flir E45
thermal imager. It cost $12,000.

We just demoed a cool new thermal imager, mounted on a nice little
stand, with its own display and also USB interfaced for pics or
movies. They're going to let us keep it.


--

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lunatic fringe electronics

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Cursitor Doom wrote:
On Mon, 06 Mar 2017 00:56:56 -0600, Foxs Mercantile wrote:

It is. But some people have difficulty accepting anything more
complicated than a light bulb, or more expensive than a pack of
cigarettes.


For the *real* cheapskates out there, there's this alternative:

http://www.ebay.com/itm/201842524936

Claims to be able to handle up to 100A!



Let's see you use it to find a stray 100 mA DC on a crowded circuit
board.


--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)


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John Larkin wrote...

We just demoed a cool new thermal imager ...


Names, please. And results, later.


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- Win
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"Winfield Hill" wrote in message
news
John Larkin wrote...

We just demoed a cool new thermal imager ...


Names, please. And results, later.


--
Thanks,
- Win


We don't believe it until there are pictures.


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On 6 Mar 2017 18:06:30 -0800, Winfield Hill
wrote:

John Larkin wrote...

We just demoed a cool new thermal imager ...


Names, please. And results, later.


I'm not sure I can name names yet. It's still in development.

We've become sort of a beta tester for these people. They send us
units and get our feedback, and we can keep them. Or maybe they just
like coming to San Francisco.


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lunatic fringe electronics

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Phil Allison wrote:
John Larkin wrote:



I have a clamp-on ammeter that pretty much does that, although it just
indicates amps, and doesn't allow waveform snooping. 60 Hz waveforms
aren't terribly interesting.


** Mains current waveforms are VERY interesting, but not if all you can
see is 60Hz. A Hall effect transducer is needed to do the job properly.

The one is use is by LEM and has response to 100kHz, allows me to see
currents as low as 1mA and up to 100A peak.


.... Phil


I used to like using a Tek Hall sensor probe. I liked it checking DC shorts
on boards.

Greg
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On Tue, 7 Mar 2017 09:11:34 -0000 (UTC), gregz
wrote:

I used to like using a Tek Hall sensor probe. I liked it checking DC shorts
on boards.
Greg


Yes, but have you seen the prices?
http://www.tek.com/current-probe
The cheapest model that does DC is $1,600.

I rolled my own. I took an old Honeywell SS495A Hall effect sensor,
built a suitable amplifier, hot melt glued it to a piece of plastic,
and calibrated it by shoving DC through various PCB traces. It's
ugly, not very sensitive (3mv/gauss or 30uV/uT), and goes nuts near
magnetic fields from xformers, inductors, steel mounting brackets,
wall warts, etc. However, it's cheap and easy. I don't use it for
troubleshooting very often.

The original suggestion sounds much like an RF current probe.
http://www.lowfer.us/k0lr/currprob/currprob.htm
https://interferencetechnology.com/the-hf-current-probe-theory-and-application/
However, these cannot be used to measure current though a PCB trace.



--
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Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


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On Mon, 06 Mar 2017 20:56:02 -0500, Michael A. Terrell wrote:

Let's see you use it to find a stray 100 mA DC on a crowded circuit
board.


Oh come along now. You know it's not intended for that sort of usage!
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On Mon, 06 Mar 2017 20:56:00 -0800, John Larkin wrote:

Or maybe they just like
coming to San Francisco.


Unlikely. ;-

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Jeff Liebermann wrote:
On Tue, 7 Mar 2017 09:11:34 -0000 (UTC), gregz
wrote:

I used to like using a Tek Hall sensor probe. I liked it checking DC shorts
on boards.
Greg


Yes, but have you seen the prices?
http://www.tek.com/current-probe
The cheapest model that does DC is $1,600.

I rolled my own. I took an old Honeywell SS495A Hall effect sensor,
built a suitable amplifier, hot melt glued it to a piece of plastic,
and calibrated it by shoving DC through various PCB traces. It's
ugly, not very sensitive (3mv/gauss or 30uV/uT), and goes nuts near
magnetic fields from xformers, inductors, steel mounting brackets,
wall warts, etc. However, it's cheap and easy. I don't use it for
troubleshooting very often.

The original suggestion sounds much like an RF current probe.
http://www.lowfer.us/k0lr/currprob/currprob.htm
https://interferencetechnology.com/the-hf-current-probe-theory-and-application/
However, these cannot be used to measure current though a PCB trace.



I was using a NASA owned probe. Thought about trying to make one.

Greg
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Cursitor Doom wrote...

Michael A. Terrell wrote:

Let's see you use it to find a stray 100 mA DC
on a crowded circuit board.


Oh come along now. You know it's not intended for
that sort of usage!


I ordered one from Newark, and plan to use it
on my messed-up switching power-supply designs.
Qualitative results will be fine.


--
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On Wed, 08 Mar 2017 05:44:39 -0800, Winfield Hill wrote:

I ordered one from Newark, and plan to use it on my messed-up switching
power-supply designs.
Qualitative results will be fine.


Mine arrived today. I plan to monitor fuel injection impulses with it
firstly just to see what kind of di/dt responses it's capable of. I'm not
quite as confident as you are, though!


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Cursitor Doom wrote...

On Wed, 08 Mar 2017 05:44:39 -0800, Winfield Hill wrote:

I ordered one from Newark, and plan to use it on my messed-up switching
power-supply designs.
Qualitative results will be fine.


Mine arrived today. I plan to monitor fuel injection
impulses with it firstly just to see what kind of
di/dt responses it's capable of. I'm not quite as
confident as you are, though!


I do a lot of fast HV pulsing circuitry, and don't
expect it'll be helpful for that kind of work. But
the 5MHz bandwidth should be fine for looking at
inductor current ramps, cap charge-discharge, etc.


--
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- Win
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On 2017-03-08, Winfield Hill wrote:
Cursitor Doom wrote...

Michael A. Terrell wrote:

Let's see you use it to find a stray 100 mA DC
on a crowded circuit board.


Oh come along now. You know it's not intended for
that sort of usage!


I ordered one from Newark, and plan to use it
on my messed-up switching power-supply designs.
Qualitative results will be fine.


a few years back there was talk of using a video head from a VCR
(after removing it from the drum) to probe AC currents. It should be good
to a few megahertz. a core from an ethernet transformer with a gap
added could be another option. a spool-shaped inductor would
probably work too.


--
This email has not been checked by half-arsed antivirus software
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On 8 Mar 2017 18:53:52 GMT, Jasen Betts wrote:

On 2017-03-08, Winfield Hill wrote:
Cursitor Doom wrote...

Michael A. Terrell wrote:

Let's see you use it to find a stray 100 mA DC
on a crowded circuit board.

Oh come along now. You know it's not intended for
that sort of usage!


I ordered one from Newark, and plan to use it
on my messed-up switching power-supply designs.
Qualitative results will be fine.


a few years back there was talk of using a video head from a VCR
(after removing it from the drum) to probe AC currents. It should be good
to a few megahertz. a core from an ethernet transformer with a gap
added could be another option. a spool-shaped inductor would
probably work too.


A little unshielded drum-core inductor is a handy h-field probe.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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On Tuesday, March 7, 2017 at 1:21:14 PM UTC-5, Cursitor Doom wrote:
On Mon, 06 Mar 2017 20:56:00 -0800, John Larkin wrote:

Or maybe they just like
coming to San Francisco.


Unlikely. ;-


Maybe they could not find any flowers :

https://www.youtube.com/watch?v=bch1_Ep5M1s

Sorry I did not get the studio version, but this one looks interesting.

But I hate to say it, you will never catch me dead anywhere in California. Maybe fifty years ago but not today, even if I could afford the rents there.
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John Larkin wrote:
On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
wrote:

https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series
resistance and you have a *very* cheap current probe for your
scope.


I have a clamp-on ammeter that pretty much does that, although it
just indicates amps, and doesn't allow waveform snooping. 60 Hz
waveforms aren't terribly interesting.

My real problem with current measurement is DC, on PC boards. We
want to know how much current, say, an FPGA is using. Sometimes I
include current shunts in a layout, but sometimes I don't.

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible.
You can measure millivolt and microvolt drops across traces and
vias.




You just described that PCB trace current probe; just use known trace
length - with known width you get approximate current.


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On Thu, 09 Mar 2017 22:43:29 -0800, Robert Baer
wrote:

John Larkin wrote:
On Sun, 5 Mar 2017 14:48:51 -0000 (UTC), Cursitor Doom
wrote:

https://www.sparkfun.com/products/11005

Replace the existing connector with a BNC, add a bit of series
resistance and you have a *very* cheap current probe for your
scope.


I have a clamp-on ammeter that pretty much does that, although it
just indicates amps, and doesn't allow waveform snooping. 60 Hz
waveforms aren't terribly interesting.

My real problem with current measurement is DC, on PC boards. We
want to know how much current, say, an FPGA is using. Sometimes I
include current shunts in a layout, but sometimes I don't.

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible.
You can measure millivolt and microvolt drops across traces and
vias.




You just described that PCB trace current probe; just use known trace
length - with known width you get approximate current.


I do that. But multi-layer power pours are not such well-defined
resistors.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

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On Wed, 08 Mar 2017 22:58:08 -0800, jurb6006 wrote:

Sorry I did not get the studio version, but this one looks interesting.


Certainly did!

But I hate to say it, you will never catch me dead anywhere in
California. Maybe fifty years ago but not today, even if I could afford
the rents there.


It all seemed to go tits-up right at the dog-end of 1969, around the time
of the Alta Mont free concert and that awful business involving Charlie
Manson and his 'Family' - and never recovered.

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Default A useful addition to your toolkit

John Larkin wrote:
On Sun, 5 Mar 2017 16:18:50 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 05 Mar 2017 07:44:18 -0800, John Larkin wrote:

I have a clamp-on ammeter that pretty much does that, although it
just indicates amps, and doesn't allow waveform snooping. 60 Hz
waveforms aren't terribly interesting.


Indeed they're not. But your meter is presumably *only* designed for
use at 60Hz, I would imagine. Hook it up to a 100Hz signal and
you'll see nothing at all in all probability. ;-)

One can use existing switcher inductors as current shunts. I wish I
had a PCB trace current probe, but that's probably not posssible.
You can measure millivolt and microvolt drops across traces and
vias.


Do they even exist? That would be amazing but no doubt *way* beyond
what I can justify to splash out on as a mere hobbyist.



A 1" long, 20 mil wide 1oz trace will be about 25 milliohms. 1 amp
makes 25 millivolts, and lots of cheapish DVMs will resolve that well
enough. You probably need a bench DVM with microvolt resolution to
measure, say, 1 amp running through a via, but you could build a
little microvolt meter or amp pretty easily. PCB trace and via
resistances need to be calibrated, which is only a minor nuisance.

Here are some pcb-trace shunts, down near the connector:

https://dl.dropboxusercontent.com/u/...ower_Board.JPG

One of the great mysteries of electronics is "where is the current
going?" Sometimes a thermal imager helps figure that out. A little
magnetometer would be fun, not hard to do these days.


I once asked if a discarded head from an old, old hard disk could do
that.

There used to be a four-pin probe for PCB current measurement, in the
late 80s, but I can't find it. They're probably on ebay but I don't
know what name to search for.




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John Larkin wrote:
On Sun, 5 Mar 2017 15:07:41 -0600, Foxs Mercantile
wrote:

They do make special current probes specifically for doing traces
on a PC board. without cutting traces or requiring a loop of wire.
http://www.power-mag.com/pdf/feature_pdf/1327592496_TTI_Layout_1.pdf


Looks expensive, and I'd guess not very accurate.


There's one on ebay now for $750.




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