acac-dcesp8266how-does-it-work
I was looking at these new IOT devices coming from CN that are designed to replace your standard wall switch with an ESP8266 smart-switch.
It seems there are two types: A) the typical one where the AC-DC circuit needs to be feed with a Neutral and a Hot wire and B) one which only requires the Hot/Live AC (220V) wire.
What kind of circuit are we talking about and how could we implement one from scratch ?
Bonus points for example schematic. 🙂
Why not consider placing your small Arduino board and its power source in the electrical box where the light bulb is located?
From your diagram it appears that the powered 220VAC feed and return line are both in the electrical box at the light fixture.
Edit to Add an Alternate Idea to try out. There is too little data regarding the Lifx bulb to know if this is even feasible at all. So you would have to simply try it.
The idea is to remove the wall switch from the AC circuit and instead wire it into the MCU board. Then wire a small transformer across the AC lines that come to the switch box. This would likely have a low turns ratio and would operate off the current that passes through the special LED bulb unit. An AC power converter on the other side of the transformer would convert AC to DC power.
A couple of things.
A very small point, the UK is in Europe, and AFAICR we have had 3-pin plugs, 3-wire cables, since the late 50's.
My house was rewired in the 80's, and we have Earth Leakage Circuit Breakers (ELCB) on every circuit. So even if I stuck a fork into my toaster while grabbing a copper water pipe, I'd expect it to trip (I am not willing to back this up with evidence :-)
When I have visited continental Europe, I am pretty sure that I've seen the same ELCB technology in use.
I suggest that is even more effective than having an Earth connection; after all, if I touched the correct bit of wire in your toaster with my fork, without touching anything else, the Earth connection via a plug would do me no good. Further, unless the device had a metal case connected to Earth, I don't think I am much more likely to touch both Earth and live than just live alone.
I imagine the cost of rewiring all of the houses in Europe which have two-wire cabling t have three-wire would be very large. However, upgrading the distribution panel with ELCB is pretty simple (a drop in replacement in some cases for an old fashioned fused unit), and could be caused to happen more easily when electricity metres need replacing.
Best Answer
The device is taking parasitic power from the circuit it is controlling. This is a bit tricky.
simulate this circuit – Schematic created using CircuitLab
Figure 1. The basic setup. Note there is no true neutral connection to the controller.
Figure 2. A triac controller output waveform. In the off (0 V) periods of the waveform the mains voltage is applied across the switch. Power can be "stolen" to charge up a reservoir capacitor during the off time but a small current must flow through the load.
Note that for this to work the RMS voltage to the load will be reduced as the full wave is no longer being delivered.
Figure 3. An Elektor circuit based on the Siemens LSB0586A touch dimmer. Source: SeekIC.
You might get some ideas by studying the schematic of Figure 3.
You may find that this circuit, designed in the days of incandescent lamps, may not work well with LED and CFL lamps.
Further improvements may be possible with MOSFET switches rather than triac as the mains can be interrupted at any point in the cycle to generate a precise voltage drop across the switch. I too would be interested in a good application note for one of these ICs.