I am about to embark on a home automation project, but I'm having trouble finding Wifi based IoT devices which can be powered from a standard two wire light circuit.
The idea is to replace light switches in each room with smart switches, powered from the light circuit, which also do things like monitor temperature, movement or anything else I can hook up to an Arduino. I could power the low voltage side with batteries, but I don't want the hassle of having to keep replacing them.
Most devices on the market designed to go behind a light switch, such as remotely operated light switches/dimmers expect a three wire lighting circuit (live, neutral and load) at the switch. In the U.K. our circuits are almost exclusively two-wire, i.e. only the live and load wire come two the switch, while only the neutral and load wire goes to the light fitting.
I obviously don't want to have to re-wire my house to make all of the light switches three-wire, but I have only been able to find one device which says it can do what I want without re-wiring (and it doesn't do Wifi).
What I want to know is how this circuit works, so I can work out if I can build something similar myself (given the usual caveats regarding circuits which run on mains voltage). Alternatively, if this circuit has a name, knowing it should help me find a power supply which does what I want.