Electric fence

[Marco]

If you can make the RC time large enough you can just treat the pulse as a dirac pulse and it works even when the pulse changes a bit. Or they could measure two pulses with two different resistors, but the large resistors seem to be in series.

What's the value of those large resistors? It's hard to read the colours from the video.

PS. maybe they switch an extra small value capacitor in series with the ground plane to get two different measurements with two unknowns from two pulses? (ground plane parasitic capacitance to earth and pulse amplitude.)

[PlainName]

What's the value of those large resistors?

I'll let you know at the weekend

[Marco]

Here's a patent for a different type, they make the handle conductive so they can use the body capacitance as a decent ground relative to the capacitance of their capacitive divider (ie. they make the divider << 100 pf).

https://patents.google.com/patent/US9829515B1/en

Though that still doesn't explain how the hotline one works. AFAICS the capacitance to ground will be significantly smaller and less predictable, making everything harder.

PS. I guess I'm making it harder than it needs to be, I guess it's just a resistive divider and a peak detector, treating the ground plane stray capacitance as a very temporary earth. I was thinking all the parasitic capacitances of the components would mess it up, but I'm probably overthinking it.

PPS. works well enough in simulation as long as capacitance to ground is more than a couple pf and the capacitance across the top resistor is small enough.

[PlainName]

PS. I guess I'm making it harder than it needs to be, I guess it's just a resistive divider and a peak detector, treating the ground plane stray capacitance as a very temporary earth.

That's what I would guess too, and how I would look at doing this. I have an advantage in that I can use actual ground (since it would be an automated monitor without a user holding it), but I would still like it capacitively coupled.

[PlainName]

Photos attached - they are big for clarity.

There isn't a decent ground plane on this, and just to make sure I operated it using plastic tweezers so my hand was relatively distant. There was not discernible difference to normal operation, so I don't think the user is part of it.

Components around the hot end, rounded to nearest E24 value:

R8	10M
R9	10M
R10	510K
R11	7.5K
R2	10M
R5	10M
R54	470K
C2	3.6uF
C4	1nF

[Marco]

"C2      3.6uF"

Doubt

[PlainName]

Yeah, but that's what it measured (albeit in-circuit). I'll take another look