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Quick and Easy Light Sensor Project

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  • Quick and Easy Light Sensor Project

    I've really been wanting to add a light sensor to the back (shadow side) of my house and then use that, in place of a sunset calculation, to turn on my lights at dusk. I considered doing this with a Z-Wave luminance sensor but didn't want the hassle of changing batteries, especially during the winter!

    So... I bought a bag of photo-resistors from Radio Shack and started messing with them and my ADIO-100. I discovered 2 things: The analog resolution of the ADIO-100 plug-in was in 1 volt increments and ... just one sensor was not enough to register anything higher than 0 volts (down in my basement). However, combining photo-resistors in parallel did register up to 5 volts (in 1 volt jumps).

    So.. I asked one of our engineers to "fix" the resolution issue and he did that in about an hour (thanks Wade). The plug-in now resolves to 2 decimal places... plenty for what I need. I then ran some plain 2-conductor low voltage wire to the shadow side of my home and drilled a small hole through the siding about 2 feet up from the ground. At the ADIO-100, one lead is connected to 5 volts and one lead is connected to an analog channel. On the other end (through the siding), I soldered 2 of the largest photo-resistors in parallel, insulated the leads with heat shrink tubing and mounted them flush with the siding. A small dab of clear silicone caulk seals the hole and covers the sensors.

    During the afternoon, the sensors were reading 4.5 volts (partly cloudy day) and I monitored the voltage, as well as the relative light levels inside to "eyeball" the correct setting for turning on my inside lights. For me, 2.5 volts is about right. I'll need a few days to tweaking to fine tune it.

    Last step... the events. For this, I created a "status device" (my terminology for what others typically call a "virtual device") called "Inside Light Device" Then, I created an this event: Inside Light Device is turned on when voltage is between 0 and 2.5 volts AND Inside Light Device is Off. That condition prevents to the event from continuously firing below 2.5 volts. Next event actually turns the lights on when the Inside Light Device has been on for exactly 2 minutes. I also created a corresponding event to turn the Inside Light Device off when the voltage is between 2.51 and 5 volts AND Inside Light Device is On.

    So... why is this better than just using a sunset calculation? Because sunset calculations are of no value, if you have to manually turn on the lights because of a rainy, stormy, overcast day!
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