The Natural Philosopher wrote:

Pete wrote:

Is it possible to power an LED from a light switch (live only connections,
and possible earth) so an illuminated LED can indicate if the light is on or
off?




Yes. Its horrendously inefficinet tho. You need a diode in addition to
the LED wired in series, and a series resistor. about 22Kohms will do
and at LEAST 2W rated. It will get hot.

Alternatively a capacitor can be used, but tis late and I can't be
bothered to calculate teh value...,

This sounds similar to a concept I used for a fermentation cupboard thermostat.
IIRC it employed the reactance of a polystyrence capacitor placed in series with
an electrolytic capacitor across live and neutral, followed by a diode from their
junction with another electrolytic from diode to neutral. I think it supplied
about 12 Vdc to the temperature controlling chip. Does any of that sound fesible
- and yes it is late here!

Richard