enen92:
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I'm thinking about buying some SSR to control some 230VAC devices (lamps mainly). I know how to choose them according to the main line voltage/amperage and also to the arduino's side "limitations". My question is about a way to find if the main circuit is connected from the arduino side. For example, if I decide to connect a SSR to a lamp and to the arduino how can I know if the lamp is turned on from the arduino if I switch the lamp on through a switch connected in paralel with the relay?
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What you ask is AC voltage/current sensor or monitor. We have some thread about it, see if it is helpful, otherwise post back here we will sharp the pencil.
http://forum.arduino.cc/index.php?topic=162326.msg1277450#msg1277450