| 摘要 |
PURPOSE:To facilitate making control circuits into ICs, to reduce power consumption and to prevent malfunction by invalidating an electrical signal obtained only when a sound at a frequency within the prescribed frequency range continues during the prescribed period. CONSTITUTION:A C sound around 5-8kHz is inputted to a microphone 1, and its output is issued as a rectangular wave signal from an operational amplifier 3. The output of an oscillator circuit 8 is inputted to an FF 13b, and a clock pulse A is outputted. A counting circuit 6a outputs said pulse to start counting. After four pulses pass, the output of a decoder 7a inverts into a level H to energize an FF 9, and a transistor 11 is conducted to light a lamp 12. If the output of the amplifier 3 is given, the pulse A is inputted to a counting circuit 6 only when the input of an AND circuit 4a is at a level H. Then the counting circuit 6 counts the frequency of the sound C. After 50 counting pass, the output of a decoder 7 attains a level H, energizes the circuit 9, and inverts an F-point output into a level L. Thus the lamp 12 goes out. |
