Liquid-level gauge:

Measuring liquid levels is a subject which never fails to cause heated debates. Does a technique exist which makes it possible to provide not only a ‘tank empty’ alarm, but also a continuous indication of the tank contents? The circuit described here operates in one of two modes: stand-alone or remote (using RS-232 communication). Once you’ve built the circuit, the fuel level in the tank of a heating system, or the water level in the gardening tank, is no longer a secret.