| 摘要 |
PURPOSE:To prevent chattering with accurate detection of light received, by setting a reference voltage for judging light received by two stages based on the output of the received light output immediately before the lighting of a light emitting element to switch the reference voltage according to the received light output at the lighting. CONSTITUTION:First, by a pulse of an oscillator X pulse, a control circuit (MCN0) is put a sample holding circuit SH into operation to sample and hold an output V5 of an amplification circuit 5 and a voltage VSH is outputted to a double-stage reference voltage circuit TH. Then, the MCN0 lights a light emitting element LED0 to output an amplified output of a light receiving element PT10 to a voltage comparator (COM), which compares the input with a reference voltage V2 obtained by subtraction of a specified level from the VSH and the results are outputted to extinguish the LED0. As the results are memorized into the MCN0, an LED1 is lighted to set the reference voltage at V1 higher than V2. When light received is detected continuously three times at the same channel repeating such comparison, it is judged that an object OB exists. This assures the detection thereby preventing chattering.
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