Thanks! So I'd be setting up a 10" long light source on the left side of my 4' wide x 3' high wall, and an 18" long light source at the bottom (maybe a strip of LED lights?). And then recess each of the receiving sensors (4 on the right side and 7 on the top) so the sensors would be far enough back that ambient light wouldn't affect them, but the light source would?A thought, its easier to make a receiver narrow beam than a transmitter.
so a light along two sides, cna be detected by detectors on the other side.
just pit a "tube" on the receiver. Does not evne have to be a tube, just two holes separated by a few mm works.
Its much easier to detect AC signals than DC ones, so amplitude modulate the emitters, means you can use an AC coupled filter as the receiver, with filtering if needed . If you MCU is fairly fast, such as a tensey Arduino, then you can apply filtering of the signal sin the MCU, to avoid false detection,
Also using the receivers like this, allows you to easily have a none linear array, you just have to move the holes / receivers.