Human body capacitance...

First we approximate the human with a sphere of equal volume.... (I wonder if that works?)

George H.

C =3D 4*pi*epsilon-zero*R, I get R~ 0.27meters, or about 30pF. That seems a bit low, but we'll wait for the experts.

Thanks George. According to wikipedia (...) 22pf is a typical value so your calculation doesn't seem to be off. I'm building a regenerative receiver which has a data slicer and the comparator seems to be oscillating at audio frequencies. It will stop oscillating if I put my finger on the comparator's inputs - I'm assuming that's like putting a small capacitor from inputs to ground?

Hello,

Your finger isn't just a capacitor, there is also resistance and you may inject interference (for example mains hum). Add some 200 Ohms in series with the capacitor when the capacitor alone doesn't stop it.

Are your sure the bias point doesn't change because of your finger, and that therefore the oscillation stops?

Best regards,

Wim PA3DJS

The military standard ESD tests for human body discharge call for an equivalent capacitance of 100 pF. That is what I had learned in school long before I started dealing with Mil-Std and commercial ESD testing.

Tom P. Albuquerque

ESD models tend to use higher values (to be conservative), wheras you'd need to use a lower value for something like a touch switch.

A seated lard-ass with lots of conductive stuff around him (eg. in a car) has more puffs than a lithe lassie standing on low dielectric constant high heels.

You should be able to read this whole paper, which has higher upper end capacitance than most ESD models (range 60pF to 300pF)

It appears the low end is more like 20-30pF if you look at touch switch information.

Best regards, Spehro Pefhany

=3DPA55...

"The Journey is the reward"

eff.com

Thanks Spehro, and others. ~100pF was the number in my mind for esd testing and such. Figures that it's at the conservative end of things.

George H.

Assume a spherical cow...

Thanks everybody!

(better power supply decoupling fixed the problem...)

Now all we need are spherical buns for the spherical burgers! ;-)