| 摘要 |
PURPOSE:To improve the optical detection characteristic for the presence of an object or the like while preventing effect of disturbed light with a simple construction by arranging a higher frequency signal and a lower frequency signal than an anticipated disturbed light to serve for flashing visible external light and for operating time. CONSTITUTION:The oscillation output of an oscillator 11 is divided into 1/2, 1/4, 1/8, 1/16 or the like with a counter 14, an infrared LED16 is flashed by 1/2 divided output higher in the frequency than disturbed lights and a visible external light is received with a photo diode 18. Then, a cyclic detection output from the reception of light via differentiation circuit 19 and an LPF21 is inputted into a shift register 13 made up of 1/4-1/6 divided output via a NAND gate 17 to be shifted sequentially. When the parallel output of the register coincides with the set parallel output of a comparator circuit 22, a set output is generated from an FF23. On the other hand, when light to be received with the diode 18 is intercepted by any object, there is no inputting into the register 13 and none of such a setting by the FF23 takes place. This can improve the optical detection characteristic for the presence of an object and the like not affected by any disturbed light with a simple construction. |
