Ac frequency to dc transducer

Claim 1

APPARATUS COMPRISING THE COMBINATION OF INPUT CIRCUIT MEANS HAVING A SIGNAL INPUT TERMINAL TO WHICH AN AC INPUT SIGNAL CAN BE SUPPLIED; BISTABLE CIRCUIT MEANS HAVING AN INPUT TERMINAL AND AN OUTPUT TERMINAL FOR PRODUCING A RECTANGULR WAVEFORM OUTPUT SIGNAL AT SAID OUTPUT TERMINAL IN RESPONSE TO AN AC SIGNAL APPLIED TO SAID INPUT TERMINAL; FIRST CIRCUIT MEANS INTERCONNECTING SAID INPUT CIRCUIT MEANS AND SAID BISTABLE CIRCUIT MEANS FOR APPLYING SAID AC INPUT SIGNAL TO SAID BISTABLE CIRCUIT MEANS; SECOND CIRCUIT MEANS FOR PROVIDING AT FIRST AND SECOND REFERENCE TERMINALS FIRST AND SECOND VOLTAGE REFERENCE LEVELS BEARING A FIXED RELATIONSHIP TO EACH OTHER; FREQUENCY DETECTOR CIRCUIT MEANS HAVING AN INPUT TERMINAL CONNECTED TO SAID OUTPUT TERMINAL OF SAID BISTABLE CIRCUIT MEANS AND HAVING FIRST AND SECOND OUTPUT TERMINALS, AND FIRST AND SECOND REFERENCE TERMINALS CONNECTED TO SAID FIRST AND SECOND REFERENCE TERMINALS OF SAID SECOND CIRCUIT MEANS FOR PROVIDING A VOLTAGE AT SAID FIRST OUTPUT TERMINAL DIFFERENT FROM THE VOLTAGE AT SAID SECOND OUTPUT TERMINAL ONLY WHEN THE FREQUENCY OF SAID AC INPUT SIGNAL DIFFERS FROM A PRESELECTED FREQUENCY; DIFFERENTIAL AMPLIFIER CIRCUIT MEANS HAVING A FIRST INPUT TERMINAL CONNECTED TO SAID FIRST OUTPUT TERMINAL OF SAID DETECTOR CIRCUIT MEANS, A SECOND INPUT TERMINAL CONNECTED TO SAID SECOND OUTPUT TERMINAL OF SAID DETECTOR CIRCUIT MEANS, AND AN OUTPUT TERMINAL; AND UTILIZATION CIRCUIT MEANS CONNECTED TO SAID OUTPUT TERMINAL OF SAID DIFFERENTIAL AMPLIFIER CIRCUIT MEANS.