Record-player switch-off device

A switch-off device for a mechanism driving a phonograph-record player, comprising:

• a pickup arm;
• a screen fastened to said pickup arm;
• a light barrier, said pickup arm traveling through said light barrier as said pickup arm swings without reaction;
• said light barrier having a pattern of light and dark;
• a sector swinging along with said pickup arm about an axis of said pickup arm;
• said screen comprising a pattern of bars applied to said sector;
• said sector having a uniform series of parallel light-permeable slots perpendicular to the direction of swing commencing in vicinity of an end corresponding to the end of disk-groove recording;
• a processing circuit comprising:
• a detector converting incoming light signals into a sequence of electric pulses;
• a square-wave shaper with switching hysteresis between high and low pulses connected to said detector;
• a first circuit branch for high level processing and having a high-level threshold detector connected in series with first memory means for determining acceptable high level pulses;
• a second circuit branch for low level processing and having a low-level threshold detector connected in series with second memory means for determining acceptable low level pulses;
• said first branch and said second branch being connected in parallel with inputs connected to an output of said square-wave shaper;
• adding means connected to outputs of said first memory means and said second memory means for adding high level and low level pulses;
• comparator means connected to an output of said adding means and having a stored time reference;
• an output stage for carrying out a switch-off order, said comparator means comparing digital time values, said switching hysteresis rendering interference frequencies ineffective as superimpositions;
• said slots having a spacing and a width on the order of 200 micrometers;
• a region of slots being positioned on said screen so that said region begins at the commencement of a sidetracker sharp range, said sidetracker sharp range being a standardized range between a last marker groove and a last modulated groove and being positioned before commencement of a switching groove;
• said screen comprising a section of transparent sheet having a length corresponding to a light-and-dark bar zone at the end of a path in form of an arc of a circle applied to the periphery of a normal to the sector radius;
• said light barrier travelling through 1.5 units of complete information, where one unit of complete information is substantially equal to one light-and-dark field, said processing circuit processing 1.0 units of complete information for switch off.