| 摘要 |
PURPOSE:To prevent the malfunction of the auto-player by discriminating the light of the light emitting element which detects optically the record disk on the turntable from the ambient light. CONSTITUTION:Three units of through-holes 2a, 2b and 2c are provided on turntable 1 to decide the size of the record disk; light emitting diodes 4a, 4b and 4c are provided on substrate 3 to correspond to the three through-holes; and photoelectric conversion element 5 is provided at the upper part of table 1 to receive the light from the light emitting diode respectively. At logic arithmetic circuit 6, three-phase pulses A, B and C of 1KHz are formed from pulse P of about 10KHz with amplitude modulation given to 10KHz, and then emits diodes 4a, 4b and 4c in time division with every 1m second each. The output of element 5 which received the light from the light emitting diode is drawn out only for the AC component near 10KHz through band-pass filter 14 and then allotted to signals G, H and I synchronized with pulses A, B and C each after rectification. Then signals J, K and L are obtained via AND gates 12A, 12B and 12C each to identify three different types of record disks. |
