| 摘要 |
PURPOSE:To easily attain record protection even if there is no protecting jacket by providing a photocoupler for converting reflected light by a recording mark formed on a disk into an electric signal, a waveform shaper for converting an output signal from the photocoupler into a control signal for a controller and a monostable multivibrator. CONSTITUTION:When the reflected light from a non-recording area (d) of the disk 5 is detected and converted into an electric signal by the photocoupler 1, a signal (g) is obtained. A waveform-shaped signal (h) is obtained from the waveform shaper 2 to trigger the monostable multivibrator 3. An output pulse (i) from the multivibrator 3 is sent to the controller 4 as a control signal. When the recording mark is detected, the output of the multivibrator 3 is turned to '1' and the controller 4 discriminates the validity of recording. If the recording mark is not detected because of the adhesion or the like of a black tape to the recording mark, the output of the multivibrator 3 is turned to '0' and the controller 4 discriminates the invalidity of recording to stop the recording operation.
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