| 摘要 |
A frequency responsive switching circuit that, in the preferred form, includes circuit means for generating a periodic first electrical signal. The first electrical signal is applied to a retriggerable monostable multivibrator having as its output a second electrical signal. A timing circuit associated with the retriggerable monostable multivibrator controls the duration of the output pulses constituting the second electrical signal. If the period of the first electrical signal is less than a predetermined amount, the second electrical signal is maintained at a fixed voltage level due to continuous retriggering of the multivibrator. The second electrical signal is applied to the data input of a shift register and the first electrical signal is supplied to the shift register as a trigger input. Multiple bit outputs of the shift register form the inputs to a gate circuit. If the second electrical signal is maintained at the fixed voltage level for a plurality of periods of the first electrical signal, then the gate circuit produces an output signal indicative of this circumstance. Thus, if the period of the first electrical signal, for a plurality of its cycles, is below a predetermined amount of time, an output signal is produced. |
