| 摘要 |
PURPOSE:To discriminate two kinds of frequency of an AC signal with a simple circuit, by using a photoisolator and a retriggerrable monostable multivibrator. CONSTITUTION:Periods of two frequencies f1 and f2 of an AC signal supplied to input terminals 11 and 12 are denoted as T1 and T2 respectively, and a width T0 of the output pulse signal of a retriggerrable monostable multivibrator 3 is set to the intermediate value between frequency periods T1 and T2. When an AC signal e1 of the frequency f1 is supplied to input terminal 11 and 12, a photocoupler 2 is turned on for coming of the positive-polarity signal to take out the earth potential and is turned off for coming of the negative-polarity signal to take out a voltage VCC. This pulse signal e2 is supplied to the retriggerable monostable multivibrator 3, and an oscillation pulse signal e3 is outputted from an output terminal 4. Meanwhile, when the AC signal e1 of the frequency f2 is supplied to input terminals 11 and 12, the continuous output signal e3 of a constant level is outputted. |
