RFID pet feeder

Step 5 Add proximity sensor

Hook up the IR sensor to analog ch 4, with an LED to show that it works. The schematic shows only this step, for clarity. In your Arduino code you have to set a threshold value above which the sensor output triggers action to keep the door open. With a simple code like below you can test what the output is when you put your hand or other objects at various distances. 

Code for testing the IR sensor can be found here:
http://www.writtensound.com/arduino/cat_feeder.htm


The sensor has an optimal range. Closer to, or farther away than that, the output will be low. The sensor used here (Sharp GP2D120) has a range of 4-30 cm.  Mount it in such a way that when the cat is eating, his head is at a distance that makes the output reliably cross your threshold, and set the threshold at a value that doesn't give a lot of false positives. My sensor output hovers between 50 and 150 with nothing in front of it, and increases to over 230 when anything is within 10cm, so I set the threshold at 200. Also, mount it in a way that the door itself does not activate it. The code is about the same as step 4, but with the IR added. Now the door will never close whenever something is in the way.  

code: http://www.writtensound.com/arduino/cat_feeder.htm