> Could you comment on what effect frequency has - for example
> choice of capacitor value and if the reactance has any bearing

PIC drive current will probably be a primary energy transfer limitation.

Energy from pin =3D pin current x pin voltage (as ever) =3D say 20 mA x 5V =
=3D100 mW.
Say assume about half that available.

Capacitor energy =3D 0.5 CV^2.
Capacitor power =3D energy x frequency =3D f x 0.5 x C x V^2.

Say pump caps are 0.1 uF. F =3D 100 kHz. V =3D 4V say (Vdd - 2 diode drops
less a bit).

Power =3D E5 x 0.5 x E-7 x 16 =3D 80 mW

Time to charge capacitor =3D  V x C / I
At say 10 mA =3D

       time =3D 4 x E-7 / E-2 =3D 40 uS.

At 100 kHz half cycle =3D 5 uS.

In practice I mean may be more like 20 mA (regardless of what spec
sheet says :-) ) so say 20 uS to charge,.
Still too slow.

Smaller caps will improve charge rate but reduce energy transfer rate.

More drive seems needed.

Inductive solution looks nicer by the moment.
See my prior post for easily available inductor.
If this is for one to few off see me for some inductors.

Maybe even many off for $ :-).

Inductor driver can be made fail safe by capacitor driving transistor
with a pull "down" on base/gate. If driver stalls drive will stop.

Otherwise, stalled driver with gate / base driven may produce
different sort of signals.

__

My prior mentioned piezo pulser MAY be able to be made to work without
much effort and would be a great talking point!!!
(And rat repeller to boot)(They claim)





   Russell
--=20
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