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.




---
This email has been checked for viruses by AVG.
http://www.avg.com