In the last post, we successfully got a laser/sensor pair working with the laser tripwire test. This is great, but my design calls for 72 of these tripwires (36 on the X-axis and 36 on the Y-axis). Unfortunately, the Arduino Uno only has 14 digital input/output pins. So we need to find a way to read signals from 72 phototransistors with only 14 IO pins to work with. In this post, we’ll be testing a method of reading many inputs with just a few Digital Input pins.