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I have been doing home automation for my home using Arduino and Android. I have been able to control the device through WiFi successfully.

Here is the scenario.

  1. Since all the appliance that I control has been pre-wired when my house was built, it can be controlled through physical switches from switch board.
  2. Also I can wire up the appliances to control through my Arduino WiFi.

My problem is how to get the status of the appliance? If I switch ON the appliance through my Arduino, I will know the status of each appliance that I control. But how to get the status of the appliance that has been controlled through physical switches? Is there any electronic circuits available to get the physical status of the switch? Thanks in advance.

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Just to clarify, you want to know how your automation system can sense if a device has been manually turned on (from a light switch, etc. not via the automation system?) Also we need to know how your systems is wired, is it like a dual switch, like this electronics-project-design.com/images/LightSwitchWiring.GIF where one is a switch and the other is a relay? Also knowing the voltage, and amperage of the devices would help, along with what types of devices are you controlling (only lights, or different devices?) –  Garrett Fogerlie Dec 16 '12 at 7:14
    
You can connect the power pin of the device you control to an opamp (comparator ) , then check through arduion pin the status of the opamp output , high or low ... very simple .. –  xsari3x Dec 16 '12 at 10:18
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@xsari3x -- Careful. In the case presented here (line-level "appliances"), advice like that may be incorrect or very dangerous. –  DrFriedParts Dec 16 '12 at 19:35
    
@DrFriedParts you are right –  xsari3x Dec 18 '12 at 14:35
    
@Garrett Fogerlie -- Thank you for the reply Garrett. Ya your understanding is right. The image you referred was how exactly I have made the arrangement. One switch will be the actual physical switch and another switch will be the relay controlled by Arduino. My load that is to be controlled operates at 230V AC with 5A current rating. I am interested in controlling CFL light, fan and my music system. So with this scenario, I don't have idea on how to get the status of the device that was switched through physical switch. Help me to find out the solution. Thank You:-) –  Spark Dec 19 '12 at 6:02
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2 Answers

Typical, commercial domotics / home-automation systems do not use the standard mechanical on/off switches, but smart switches. The smart switches, usually have a dedicated, tiny microcontroller, that is able to interact with the main domotics controller, to request the associated appliance to be turned on / off.

Standard 1-way mechanical switches need to be always left in the ON position for domotics contol to work. Turning such switches off, overrides the domotics controller's view of the last operational state. So, the only way is to have a feedback mechanism using some kind of a sensor (usually a current sensor, but could be other kinds - e.g. a simple LDR for light sensing), that reads appliance state, and notifies the domotics controller.

PS> Standard warnings regarding the hazards of working with AC line voltages apply. However for the purpose of this answer, lets assume that you know what you need to know.

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230V AC is dangerous people-killing voltage and you want to isolate it from the touch safe low voltage portion of your system.

See http://openenergymonitor.org/emon/buildingblocks and click on the section of Non-invasive current measurement, Non-invasive voltage measurement.

Volt measure (transformer or optical isolator IC) tell you if the mechanical switch is ON but the machine may be un-plugged or on-machine switch may be off or the light bulb may be burnt. Current sensing tell you definitly if it is taking current and how much.

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