Patent ID: 8744773

Claim:
A rain sensor comprising: at least one hygroscopic member; an electronic sensor that detects an amount of expansion of the hygroscopic member upon absorbing moisture; a computer processor; and a memory connected to the computer processor and pre-programmed with an algorithm that enables the computer processor to determine the presence of rainfall and generate a shut off command, the determination being based on the signals generated by the electronic sensor indicating that the at least one hygroscopic member has expanded a predetermined amount and has expanded at a predetermined rate; wherein the algorithm causes the computer processor to periodically calculate a dry-to-wet threshold and a wet-to-dry threshold, to periodically determine minimum and maximum set points for a range of travel of a magnet operatively coupled to the at least one hygroscopic member, and to generate the shut off command when the magnet has moved a predetermined percentage away from the minimum set point.