| 摘要 |
PURPOSE:To correct automatically a temperature, and to always detect an object by setting a reference level of a detecting means in accordance with a stationary variation of an output signal of a cds. CONSTITUTION:When a light of a light emitting device 6 is reflected by a needle 8 of a tachometer 7, an image is formed onto a cds 1 by a lens 9. When the cds 1 receives a reflected light of the needle 8, the impedance drops, and it conducts and outputs voltage V1. The voltage V1 is inputted to a - input pin of an LPF 3 through a voltage follower 2 being a buffer, and the LPF 3 suppresses a fact that a waveform of a reference level V2 rises together with the voltage V1 by an impedance drop by the reflected light of the cds 1. Also, the polarity becomes opposite by making it pass through the LPF 3. Moreover, by making said voltage pass through an amplifier 4, it is outputted to a - input pin of a comparator 5 as a reference level V2 of the same phase of the voltage V1. |
