| 摘要 |
PURPOSE:To attain high sensitivity of the light receiving device and to simplify the configuration by using a program of a microcomputer so as to discriminate frequencies of dual modulation infrared beam pulse lights from a light emitting device. CONSTITUTION:When a high frequency signal subject to 100% amplitude modulation by a low frequency signal is inputted to a light receiving element 11, an external interference light and noise generated in the inside of the element 11 appear simultaneously as an electric signal of the element 11. The signal in a frequency range close to a tuning frequency including the noise is selectively amplified by a tuning amplifier 12. That is, the noise component is remarkably eliminated and the signal component is emphasized. When the resulting signal is detected by a detector 13, the signal having the same frequency as that of the low frequency signal from the light emitting device is obtained and it is amplified by an amplifier 14 and inputted to a comparator 15. The comparator 15 sends the signal whose level is a prescribed level or over to a microcomputer 16. The microcomputer 16 compares the signal with a signal of a prescribed frequency based on the program and sends a coincidence signal to an output section 17 when the prescribed frequency signals are consecutive for a prescribed time. |
