On Sun, 4 Oct 1998, James Cameron wrote:

- snip -

This will work, BUT 2 all-important parts are missing: R1 and R2, also
the zener is misplaced:

>
>                                       +5V          0V
>                                        O           O
>                                        |    C2     |
>                                        *----| |----*
>    240VAC                              |           |
>    hot    R1     C1                    |           |     neutral
>    O-*--/\/\/\---| |-------*---|>|-----+           *-----O
>      |                     |                       |
>      |                  K  -                       |
       |                     A   Zener               |
       |                  A  -                       |
       |    R2               |                       |
       +--/\/\/\-------------*-----------------------+

> I'm not qualified to tell you how to do this safely.

Neither am I but I did use it ;)

> Perhaps others can fill it in with component values and limits.

The key is: Zc = 1 / ( 2 * PI * C ) [ohm, Farad], where Zc is considered
the current limiter for the Zener current. Currents above 30 mA are not a
good idea. C1 must be capable to operate at that current and peak mains
voltage for a long time.

R1 is dimensioned to limit inrush at Vpp = 1.42 * Vmains to the limit
admissible zener current, and should be a fuse resistor or at least
flameproof, and R2 drains the charge in C1 if it retains any when the
power cord is removed, and prevents zapping the operator. It's typically
something like 470 kOhms, 0.5-1 Watt (for higher voltage withstanding
capability).

BE AWARE that the circuit must be assembled to meet IP2 class or better,
that is no metallic parts can be touch-able by any person and because of
the hot chassis no connectors leading out from the circuit are safe. USE
THIS AT YOUR OWN RISK. And I'm also not qualified to tell you how to do it
safely ;)

Peter