Frequency detection apparatus including voltage responsive means coupling first and second capacitor charge-discharge circuits

Claim 1

Apparatus for determining whether the variable input frequency of a series of periodic electrical signals is greater than or less than a predetermined frequency, comprising in combination: a first capacitor; a first resistive circuit path connecting said first capacitor to a unidirectional voltage source such that said first capacitor is thereby charged at a predetermined rate; first variable resistance means having a control electrode adapted to receive said periodic electrical signals and having a transconductive path connected to said first capacitor, said transconductive path being periodically rendered conductive in responsE to said periodic electrical signals so that said first capacitor is thereby discharged; output means for performing an indicating or control function; a second capacitor; a second resistive circuit path for charging said second capacitor at a predetermined rate; second variable resistance means connected to said second capacitor so that said second capacitor is discharged in response to signals received by said second variable resistance means; means for operating said output means when said second capacitor charges to a predetermined voltage; voltage responsive means operatively connected between said first capacitor and said second variable resistance means for actuating said second variable resistance means in response to a predetermined voltage across said first capacitor; and means for adjusting the charging rate of said first capacitor so that the frequency at which said second variable resistance means is actuated may be altered.