I'm working with my son on a 4-H project, and we have great ambitions, but very limited knowledge.
We're looking to use a motion detector to switch off the current to electromagnets that will hold the doggie door closed.
We found a Motion Triggered Room Light Kit at Jameco, and it looks like it would do the trick for us except that it's designed to turn power on when motion is detected - we need it to cut the power to the magnets so the door will swing.
The other thing we'd like to be able to do is modify it to use 2 motion detectors instead of one - one on each side of the door so it unlocks no matter which way the dog is coming through.
We'd also like to eliminate the light sensor portion, as we want it to work day and night. It looks like replacing the CDS photo resistor with a regular resister of the appropriate resistance (it looks like 100KΩ should do the trick, but I'm not 100% sure). We can simply leave the light sensor inside the box so it always thinks it's night if need be.
Here is the schematic provided with the kit:
Sorry it's not particularly good quality, I simply pulled the image from the PDF of the instructions I downloaded from Jameco
We can do the soldering and follow the very detailed instructions in the kit, but neither of us have enough electronics knowledge to be able to modify the circuit to do what we need.