| 摘要 |
PURPOSE:To prevent a wrong read of identifying information by emitting a light beam by applying a modulation by a light emission control means, demodulating it by a photodetecting means, eliminating a disturbance light, and fetching an output of only the corresponding photodetecting means by synchronizing successively with a light emission. CONSTITUTION:Light emitters 2a-2d are placed adjacently and photodetectors 3a-3d are placed opposingly, and a cassette case C is inserted between both of them. Gates 4a-4d are opened for a prescribed period by a continuous pulse signal M and selecting signals Fa-Fd. The photodetectors 3a-3d are driven by a pulse, an output signal is amplified 5a-5d and inputted to a switch 8, and by a signal synchronizing with the selecting signals Fa-Fd, for instance, when the light emitter 2a is driven, only an output of the amplifier 5a is selected and inputted to an HPF 9, only a signal component exceeding a frequency corresponding to a fundamental frequency of a modulation signal M is made to pass through, a DC signal by a disturbance light L0 is cut, a signal portion by a modulated light is fetched, compared with a reference value Vr, and at the time of H>Vr, a pulse signal S of length of one period portion of the modulating signal M is generated through a single pulse generating machine 11. According to this constitution, identifying information can be read without an error.
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