| 摘要 |
PURPOSE:To prevent malfunction due to displacement of a shut device caused by vibration or the like by providing a control circuit increasing the light emitting amount when an optical signal received intermittently from a light emitting element via the shut device reaches the operating level of a photodetector. CONSTITUTION:A slit disc 1 is fitted to a rotary shaft 2 turned proportional to a wheel, a slit 3 having a prescribed width is formed to the peripheral at an equal interval, and alight emitting diode D1 and a photo transistor (Tr)1 are arranged while clipping the slip 3. As the disc 1 is turned, a pulse current i2 flows through resistors R2, R3 to the Tr1 by using an optical signal from the D1 intermitted by the slit 3. When the level by the current i2 reaches the operating setting level of a Tr2, a current i3 flows to the Tr2 and the level of an output terminal OUT goes to a low potential. Then the diode D2 of a light emitting amount control circuit 5 is conducted by it, a current i4 flows thereto and a current (i1+i4) flows to the D1 to increase the light emitting quantity. Thus, the conductive period of the Tr2 is prolonged and made stable, the effect of the deviation of the slit 3 due to minute vibration of the shaft 2 is less and malfunction is prevented. |
