You can drop 220V to 5V using a capacitor.

The circuit can be.
Series Capacitor from Phase
Bridge Rectifier from other side of cap to Neutral
Series resistor from +ve output of Bridge
Zener Diode from other side of resistor to -ve side of bridge
Capacitor across Zener

The available current is restricted by the reactance of the capacitor. Xc =
1/(2 x pi x f x c)

example for 50Hz mains at 230VAC.

ie. 1uF ->  Xc = 1 / (2 x pi x 50 x 1e-6) = 3183 Ohms
Maximum current = V/Xc = 230/3183 = 72mA

The resistor after the bridge is a series limiting resistor. This can be
small (22R).

IMPORTANT !!! be VERY careful with this circuit, there is no isolation from
the mains. The Differential voltage for your circuit is 5V but the entire
circuit is still 230V above ground. If you put a scope probe on the circuit,
ensure that the earth lead on the scope is isolated from Ground.

*** The series Cap should be a mains rated cap (630VDC, 230VAC). You should
also place a 1 Meg resistor across it so that charge will bleed off it when
power is removed.

The 22R needs to be capable of dissipating enough power at max current. ie.
P = I^2 x R. = 22e-3 x 22 = 0.11W, use 250mW.

The Decoupling cap could be 47uF, 35V.

Regards
David Huisman
Orbit Communications
www.orbitcoms.com

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