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How to remotely monitor an appliance

X10 Status Appliances

During the course of automating your home, one will usually come across a dilemma on how to monitor a status of an appliance.  Examples can include wanting to know when a washer/dryer is finished, dishwasher cycle completed, etc...
Previous methods of getting status included monitoring the current of the appliance via a current donut, hacking the appliance so a relay or other device was installed in order to get some type of contact closure, and installing magnetic proximity sensors on the appliances dials (all of these methods are actually described in previous CocoonTech How-To's).
But, what happens when you don't want to modify your spiffy new appliance due to voiding warranty (or the WAF prohibits such actions)?
You could easily monitor a status light that most modern appliances have now as shown in Dan's previous How-To.  This method will let you monitor a light's on/off status with your home automation hardware that can detect an open collector contact closure (Modicon SECU-16, Elk Input, HAI Input, etc...).  But what happens when you don't have any wires running to that appliance from your home automation detection hardware?
This How-To will let you monitor the status of an appliance's light remotely using a standard DS10a security sensor from X-10.  Many members here already have the capability of monitoring these devices via a W800, RFXCOM, or MR26a receivers.  DS10a's are so popular we even have a thread dedicated to their non-typical uses in home automation projects  
The method described in this How-To will use a CdS photo-resistorplaced over the appliance's light, then have a DS10a trigger based on the resistance change that the photo-resistor sees when detecting those light level shifts from on to off.
The entire system can be operated off of the batteries of the DS10a so no wiring is needed (other than the wiring coming from the DS10a to the actual photo-resistor). 
First you take a DS10a and remove the magnetic sensor from its wiring.  Now you need to assemble the circuit shown below on a small bread board.  You should be able to easily assemble the components on a breadboard that can mount in a small plastic box and mount the entire assembly on the back of the DS10a sensor.
Attached Image: light sensor schematic.jpg Attached Image: rear.jpg Attached Image: rear_enclosed.jpg
Parts and Assembly
Attached Image: pwrwires1.jpg
The parts can be purchased from any electronic supplier or picked up at your local Radio Shack or Frys.  Radio Shack also sells a small circuit breadboard and plastic housing that works well for mounting it on the back of the DS10a with two sided foam type tape or glue.
If you want to use the battery supply of the DS10a for the circuit you can simply solder a wire on its positive and negative battery springs, then route those wires to the box.  I also cut some notched holed in the plastic box as well as the DS10a's cover so they would not get pinched when that cover is closed.
The DS10a's wires from the magnetic sensor are polarized so if the circuit does not work, you may need to reverse these wires.
  • Once this assembly is completed, register the DS10a to your home automation software by using the test button.
  • Then place the CdS photo-resistor over the appliances light using black tape (the wide type of 'pipe tape' works best for this).
  • Secure the wiring from the photo-resistor so the sensor maintains proper contact with the LED.
  • You may even want to try to bench test this by just using a flashlight and shine it on the photo-resistor before mounting.
  • Operate the appliance so the LED is turned on.
  • Adjust the pot until the indicator light of the DS10a blinks.
  • Turn the pot slightly more to insure a proper bios of the transistor.
Note that the circuit's sensitivity has a pretty broad range.  For instance you can make this circuit very sensitive so that ambient room light will trigger it (so it could be used as a room light level indicator for a crude dusk/dawn detector).
I would like to thank Cocooner TonyNo for helping with resources for the circuit and also the HomeSeer forums(where I remember reading a post about the idea/concept of the transistor triggered DS10a concept).