| 摘要 |
PURPOSE:To eliminate the effect of the ambient light and thus to obtain an economical detecting device which is free from malfunction by using the photoelectric conversion element to detect optically the record disk on the turntable plus another photoelectric conversion element to detect the ambient light respectively. CONSTITUTION:Three units of through-holes 2a, 2b and 2c are provided on turntable 1 to identify the record disk size, and light emitting diodes 4a, 4b and 4c are provided on substrate 3 to correspond to the three though-holes. At the same time, photoelectric conversion elements 5a and 5b are provided at the upper part of table 1 to receive the light from the diodes and only the ambient light respectively. In logic arithmetic circuit 6, the pulse of frequency of about 1KHz is converted into three-phase A, B and C to emit diodes 4a, 4b and 4c in time division and sequentially. Then the output of element 5 which received the light from the diodes is compared with the output of element 5b at comparator 13. And the effect of the ambient light is subtracted, and this output undergoes a logic operation with pulses A, B and C to obtain signals G, H and I to identify the size of the record disk. |
