| 摘要 |
PURPOSE:To prevent malfunction due to external noise by providing a current- resistor converting element or the like to a time constant circuit of a pulse input circuit of a counter and changing the charge/discharge time of the time constant circuit to change the input response frequency of the counter. CONSTITUTION:When a voltage VCON is fed between external terminals A and E, the V-C converting circuit 2 converts the voltage VCON into a corresponding current value, and the current is fed to the primary side of a photocoupler PHC. Then the primary side LED is lighted by the lightness proportional to the voltage VCON and the resistance Rx of the secondary side CdS cell is changed in response to the received lightness. Thus, the resistance Rx of the CdS cell is changed in response to the voltage VCON applied between the external terminals A and E. Further, the counter 1 detects a time corresponding to a prescribed value of an input waveform defined by r1=Rx.C at charging of a time constant circuit 5 and r2=(R1+R2).C at discharge and sets a response frequency, then a desired continuous response frequency is set by controlling the voltage VCON fed between the terminals A and E. |
