I had to leave out the PIR sensor for now. I had designed the board to use the 3x2x1 plastic enclosure that you can find in any Radio Shack. I checked that I could fit the PIR and Sonar sensors into the lid (after drilling holes), but what I didn't count on was the room that the wires and pins would take up. I couldn't fit everything in, so I need to find another project box that is relatively flat (the 1" depth exposes the box underneath the cabinet) and can accommodate everything. Ideally, I want a box that is 4.5x2.5x0.75.

So I took out the PIR and have the sonar sensor pinging continuously. It works well, but I think I'm going to do some sort of averaging algorithm on the readings. The lowering of the intensity by lowering your hand from just under the sensor (activation) is jumpy and 'locks' too quickly (when it gets an erroneous reading, thinking the hand was removed).

Below is a demonstration. What is interesting is the tapping you hear is the sonar sensor, but you can't hear it normally. I guess my phone picks it up just like video cameras pick up IR light.