| 摘要 |
PURPOSE:To detect the terminal of a record without being affected by eccentricity and external oscillation, by including a shielding plate which changes the extent of shielding in accordance with rotation of a tone arm and a photointerrupter to which the light is intercepted by the shielding plate. CONSTITUTION:A photointerrupter 1 is shielded by a shielding plate 6 so that the output of the photointerrupter 1 is linearly changed according as a tone arm 5 is moved inward, and the photointerrupter outputs the output proportional to the position of the arm, and the output becomes, for example, an output (c). Consequently, the output of a comparator 7 is inverted in the position, where a slope output (b) crosses the output (c) of the photointerrupter, and becomes a waveform (d) and is inputted to a microcomputer 3, and the microcomputer 3 turns off a pulse signal (a) which is outputted till then. Thus, the microcomputer 3 reads in a delay time T from the pulse signal output to the signal (d) input. Since the delay time T is proportional to the extent of movement of the stylus tip of the tone arm 5, a sound groove, a leading-out groove, or the last groove is detected in accordance with the position of the stylus tip of the tone arm 5.
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