A distance sensor provides basic gesture recognition and a microcontroller with wireless connectivity controls both and provides home automation integration as well.

Here’s a comparison of the performance and limitations of inductive, capacitive, photelectric and ultrasonic proximity sensors.

If you have one ultrasonic sensor and a microcontroller, you can detect plenty of useful things, like the water level in a rain barrel or the distance traveled by a tablet along a rail.

A low-cost (~$100), do-it-yourself (DIY) ultrasonic water level sensor/datalogger has been designed, constructed, and tested for use in education, citizen/community science, and research settings. The ...