Automatic control system for a defogging circuit

In an automatic control system for a defogging circuit for a glass pane having a central viewing area and which includes a plurality of spaced generally parallel elongated linear heating resistors disposed on a surface of the central viewing area of the pane, the improvement comprising:

• an electric power supply including a first bus and a second bus disposed on said surface of the pane laterally of said central viewing area and connected to said resistors for supplying current to said heating resistors, said buses extending generally transversely of said resistors;
• a control circuit controllably connected between said power supply and said first and second buses for controlling the supply of current thereto, said control circuit comprising a miniaturized unit mounted in the immediate vicinity of a corner of the pane away from the viewing area and having a control input terminal means;
• and
• a plurality of electrically conductive, moisture-sensing probes spaced apart from each other and said central viewing area at widely spaced zones on the glass pane, at least one of said probes including a conductive member having a portion running substantially parallel to and closely spaced from one of said buses, each of said probes having a portion running substantially parallel to said heating resistors of the defogging circuit, said probes each having a length, exclusive of said portion parallel to said bus, approximately the length of said heating resistors, each of said probes being sensitive to fogging of the glass pane in its immediate vicinity and having a signal output means upon which a signal appears upon occurrence of a given level of fogging, said control input terminal means of said control circuit being connected to each of said probes for receiving signals therefrom for enabling said control circuit to supply current to said heating resistors from said power supply in response to detection of fogging of said pane by any one of said probes.