A few days ago, a friend came over to talk about some microcontroller related projects. One of the topics was distance sensing, or rather proximity/movement sensing with low technical effort.
The basic idea was to detect movement of an object or person within a short distance to trigger events. Typical sensors for this kind of application would be passive infrared (PIR) modules, radiowave sensors (microwave or radar) or active infrared distance sensors. All of these can be quite pricey, perhaps with the exception of the PIR, which cannot detect objects very well.
So, I thought about how the goal could be accomplished with standard parts. Active infrared is the most simple choice. Continue reading