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I am trying to incorporate my outdoor flood lights with motions sensors into my home automation system. Specifically, I would like to sense when the lights come on to trigger other home automation actions. I thought an RF switch that provides line state to the server may work best. Any thoughts or better ideas?

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    can you tap into the lines to the lamp itself, if so then just add a relay there to trigger the signal – ratchet freak Nov 30 '14 at 14:31
  • Agreed. Control the interior switch for the lights; that makes it a standard retrofit. – keshlam Nov 30 '14 at 14:42
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There are some productive discussions here: http://forum.arduino.cc/index.php?topic=9980.0 https://electronics.stackexchange.com/questions/79794/determine-with-arduino-if-220v-ac-power-is-on-or-off

A few ideas come to mind: 1) Stick an photosensor in front of the light connected to your home automation server. Advantage is that you don't need to modify the light's circuit. Disadvantage is that you need to run 2 low-voltage wires outside.

2) Modify the circuit to have a socket, plug in a small transformer (e.g. cell phone charger) and run that wire back to your circuit. Advantage is that it is straightforward and uses off-the shelf parts. This works great if there's a junction box indoors that you can tap.

3) Use an AC-powered relay of the types here: (e.g. Tyco R10) http://www.industrialelectronics.biz/potter/potter.html Advantages: safe, disadvantage you still need to modify the circuit.

4) Use a hall effect sensor. Advantage: no need to modify the circuit, but you still need access to it.

5) Use a custom circuit consisting of a half-bridge rectifier, a resister network divider, and an optoisolator, which is basically what a wall-wart does, except that it has a transformer in it. Advantage: cheap. Disadvantage: dangerous.

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