I am thinking about making a remote control light switch that fits into the existing light switch panel. And to power up the electronics that would requires a 3.3V DC supply.

The problem is, the panel has only two wires inside - 1. Live and 2. wires that goes to the light bulb. The neutral lines is not routed through the panel box.

Hence - a typical AC rectification + zener diode or transformer circuit that I found on this website couldn't be used. There is simply no neutral.

[This schematic](http://technosyndicate.wordpress.com/2012/11/12/powering-a-low-voltage-dc-load-from-a-single-pole-high-voltage-power-supply/) is the closet thing I have come across with my google-fu. 

![enter image description here](https://i.stack.imgur.com/OfaD5.gif)

The capacitor got charged by the positive and negative cycle, I suppose.
But I want a continuous supply of DC for the microcontroller/radio, I am not sure how to modify that.

Thanks.