Arduino get data from Wall light switch

Projects General Guidance
23

Smackflad:
What I'm trying to do :
Turn on and off the lights from Wall switch (like normal rooms)
Turn on and off the lights from arduino relay

Side things :
If I turn on the lights from the wall switch I need arduino to know that I've done it.

Temporary things :
I use arduino uno.
Serial monitor + coding turn on a relay.
I have a temporary wall switch that I use to try and find the solution.

I hope that made things a little bit easier for you.
Thanks for your time.

Draw out your wring.
google ladder logic. power on the left, neutral on the right.
you have a switch connected to the left, and a light connected to the right.
there would be a wire from the switch to the light.
you have a relay COMM connection connected separately to the left.
and the relay N/O or Normally Open connection connected to the light.
the light is connected to the neutral with no change.
all wire connected to the left is black, all wires connected to the right is white all wires in the middle could be red, or black, not white.
the light will have power if either of the devices is closed. the power would not be present if all of the devices are open.
problem : the Arduino cannot turn the light off if the manual switch is provding power.
senerio #2 :
you instlal a new switch, low voltage, connected only to the Arduino
you tell the Arduino to turn on the lights and the Arduino is the only device that can turn it on.
problem is that with a device failure, you have no lights.
senerio #3 :
the light switch is a 3-way switch and a second 3-way switch is replaced by the relay. the first switch will be in either an up or a down postion, depending on the state of the relay.
the light can be turned on or off manaully at any time.
the light can be turned on or off by the Arduino at any time.
problem : electrician is required to re-wire the lighting circuit.
one great thing is that now the manufacturers are making a wall box that has both mains voltage and also low power in the same box. this way, you have everything where your electrician can see it and there are no surprises.