A Long-Range Sunlight-Resistant Photogate

Photogates play an important part of many of today’s physics laboratory experiments. They signal when an infrared (IR) beam is interrupted, thus supplying the experimenter with important timing information. Currently photogates use an infrared photodiode (IR transmitter) and a phototransistor (IR receiver). User-built photogates have a weakness though. When a photogate-based experiment is run in a sunlit room, stray sunlight, under certain conditions, can temporarily saturate the phototransistor, causing it to fail unexpectedly. In this article we present an inexpensive IR receiver module that replaces the phototransistor. It is sunlight resistant, comparable in size to a phototransistor, and requires only minor modification to housing, wiring, and programming of the existing user-built systems. This module can also be used in a system designed to communicate data from an ongoing experiment over a long range. The module is commonly used in a handheld TV remote.