This document covers the construction of a USB connected and powered photogate. This is an infrared phototransistor (switch) that is turned on and off by an infrared Light Emitting Diode (LED). The heart of this system is a Microchip PIC18 serires microcontroller. This small computer on a chip comes in an easy to use DIP package and is fairly simple to use with USB connectivity.

The purpose of the usb photogate is to provide a cheap device that can be used in a variety of different educational and hobby experiments.