1319864 Remote control of garage doors J HORROCKS 24 Aug 1971 [31 July 1970] 37105/70 Heading G1A In a control means responsive to pulsating plane polarized light and suitable for opening a garage door two photo-sensitive resistors 6 and 7 are placed inside a tubular housing 8, as shown, one in front and one behind a polarized light filter 9, and control is effected when light from a headlamp 3 equipped with polarized filter and a flasher unit 5 falls on the photo-sensitive resistors 6 and 7, the circuit 12 being designed to effect pulsation signals only and to activate an electrical door opening circuit 13. In circuit 12, Fig. 2, the photo-sensitive resistors 6 and 7 and a variable resistor 17 form a potential divider 17 connected to the base of a transistor 14 so that when planes polarized light (orientated at 90 degrees to the plane of the filter 9) falls on the photo-resistors the change in their resistances switches on the transistor 14. A transformer 15, 18 connected to the collector of the transistor 14, locks D.C. signals but allows pulsating signals to pass and switch on a further transistor 20 thereby activating a relay 21 and a solenoid controlling the garage door. In an alternative arrangement two polarization filters are inserted in the beam and the two sub beams are detected together with an unpolarized beam.
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