When I went to tech school years ago to learn electronics, one of sections of our course was to build a device to "read" stencils in the shape of letters, and have the computer (an Amiga 1000) interpret the shape. Basically a primitive form of OCR and/or computer vision. Our array was an 8 x 8 phototransistor array (64 elements); the input to the Amiga was via the 8 bit parallel port. We basically had a multiplexing scheme where we used an 8 bit shift register, setting the parallel port to output to select which "row" we wanted; once that was latched in, we switched over to "read" mode and read the outputs of the row. There was also some buffers and such built in (so we didn't blow anything by attempting to write when in read mode, etc). As I remember, it wasn't a terribly complex circuit, but still interesting nonetheless. I keep meaning to dig it up, scan it in, and post it on my website (you could make a nice low-vision "eye" using such an array made from SMT photo transistors, and a simple convex lens, all mounted in a box - would be pretty neat for a small robot).