| 摘要 |
<p>PURPOSE:To prevent the effect of disturbance by adding a light detection circuit including a light emitting element and a photodetector to a duty ratio variable oscillation circuit and detecting a change in the oscillation of duty ratios at the time of the presence and absence of an object to be detected. CONSTITUTION:A small duty pulse oscillation circuit 5 is composed of the combination of a gate circuit G1, a reversal gate circuit G2 and a time constant circuit of a capacitor C1 and resistors R1, R2. The duty ratio of the pulse oscillation output of this circuit 5 is almost determined by R2/R1 and, by making the value or R1 larger than that of R2, the duty ratio can be set, for example, to about 1/10-1/1,000. A light detection circuit 6 has a series circuit consisting of a resistor R10, a light emitting diode LD and a transistor Tr1, and a light source composed of a register R11. By this constitution, when an object 1 to be detected is absent, a phototransistor PTr1 is in an OFF-state and no AC component is added to a level shift circuit 7. When the object 1 to be detected is present, the light emitted from the diode LD is reflected from the object 1 to be detected to be incident on a transistor PTr1 and a cyclical pulse signal appears to be amplified to be applied to the circuit 7.</p> |
