I'm planning to create an ESP8266 relay module to control my lights remotely. To proceed, I need to convert the standard 220V AC power supply to DC and connect ESP8266 module.
My concern lies in the fact that in many households, there's only the "Live" or "Line" wire available at the switch, without a "Neutral" wire.
Is there a viable method to convert 220V AC to DC without needing a Neutral wire?
I've come across some mentions of using non-isolated step-down converters for this purpose, but I haven't found much detailed information. Could someone clarify if this approach is feasible or suggest alternative solutions?
It should ALWAYS be isolated and you don't need a neutral or a ground.
If you are building your own DC power supply you should use a regular isolated step-down transformer. Any power supply you buy will be completely isolated. If you buy a USB charger it will be isolated, etc.
Here in the U.S. we have a hot and a neutral (plus an "optional" ground). Most of the time the neutral is treated as hot and safely insulated, etc.
We also have something called "split phase" with two 120V hot wires that are out-of-phase. Half the house is on one phase and half on the other. That allows 240V for higher wattage appliances like ovens, clothes driers, and electric water heaters. Or for a welder or electric car charger in your garage. Some 240V Appliances don't have neutral but they have an earth ground to the chassis for safety.
Of course, relays are also isolated and with a double-pole relay you can switch both wires.
It is not advisable and in many places not legal to tap such switch connections for power. Connect to a standard power outlet instead, with proper case grounding.
Whatever you see on the internet regarding this issue will be a code violation and possibly a fire/shock hazard.
Some workarounds may work only with incandescent bulbs and maybe certain LEDs but still not recommended.
Live and neutral are usually available at the light. Place your circuit in the ceiling cavity above the light.
If you need to override the switch and turn the light off with the ESP/relay, wire the wall switch as a switch to the ESP pins (meaning no 220V connection to the switch).
Do not fudge you can cause a major fire and burn down your domicile. If the insurance company finds that they may not pay. Get an electrician to update the wiring. You have two conductors that are going to the fixture they control. If that is available you may be able to get power there.