Patent ID: 7561055

Claim:
A rain sensor comprising: a sensing circuit comprising at least first and second sensing capacitors that are sensitive to moisture on an external surface of a window; the sensing circuit further comprising at least one mimicking capacitor that mimics at least one of charging and discharging of at least one of the first and second sensing capacitors; wherein a writing pulse causes at least the first sensing capacitor to be charged, and an erasing pulse causes each of the first sensing capacitor and the mimicking capacitor to substantially discharge; wherein presence of rain on the external surface of the window in a sensing field of the first sensing capacitor causes a voltage at an output electrode of the mimicking capacitor to fluctuate in a manner proportional to fluctuation of voltage at an output electrode of the first sensing capacitor, even though the rain is not present in a field of the mimicking capacitor; wherein rain is detected based on an output signal from the output electrode of the mimicking capacitor, wherein the output signal is read at least between an end of the writing pulse and a beginning of the erase pulse; and wherein the mimicking capacitor is physically separated from the sensing capacitors, and wherein the writing pulse causes the first sensing capacitor, but not the second sensing capacitor, to charge and also causes the mimicking capacitor to charge.