I have 10 lamp in the room. Each lamp connect by using 3-way switch. That's each lamp can turn on/off by 2 switch. I want to detect which lamp turn on. The easy way is convert AC 220v from each lamp to 5v. After that connect 5v to arduino input. I have 10 lamp so I have to buy module 220v to 5v 10 module. I can't use LDR because it may not correct detection when open some lamp. Do you have any method to detect which lamp turn on ?
Using light sencitive resistors, or photo diodes, and 5 volt cabeling to the controller would cost less I think.
I can't use LDR because it may not correct detection when open some lamp.
ANY method can fail. The more parts, the higher chance of failure. The lamp will fail.
An LDR is an excellent choice.
Attach the light sencing device close to the lamp and protect it from influence of the other light sources. Know that light declines exponentially by distance.
1/R^2 from a point source.