Vehicle detector

Claim 1

A VEHICLE DETECTOR INCLUDING IN COMBINATION, SENSING MEANS COMPRISING A MAGNETIC CORE AND A HIGH IMPEDANCE COIL FOR LINKING A WEAK MAGNETIC FIELD SUCH AS THE EARTH''S MAGNETIC FIELD WHEN SAID SENSING MEANS IS PLACED ADJACENT A VEHICLE PATH, SAID SENSING MEANS GENERATING LOW FREQUENCY VOLTAGE PULSES HAVING A PERIOD OF THE ORDER OF FOUR SECONDS TO ONE-FIFTH OF A SECOND IN RESPONSE TO CHANGES IN SUCH LINKING MAGNETIC FIELD BY PASSAGE OF A VEHICLE ADJACENT SAID COIL AND DEPENDENT UPON THE SPEED OF THE VEHICLE, A MULTI-STAGE TRANSISTOR-AMPLIFIER CIRCUIT INCLUDING FIRST AND SECOND STAGES EACH INCLUDING A TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELEMENTS, CONNECTED IN COMMON EMITTER CONFIGURATION, SAID AMPLIFIER CIRCUIT HAVING AN INPUT CIRCUIT COUPLED TO THE BASE OF THE FIRST STAGE, MEANS INCLUDING A HIGH RESISTANCE CONNECTED IN SERIES WITH SAID BASE IN SAID INPUT CIRCUIT TO COUPLED SAID INPUT CIRCUIT TO SAID HIGH IMPEDANCE COIL, AND MEANS INCLUDING A FURTHER HIGH RESISTANCE IN SERIES WITH SAID EMITTER OF SAID FIRST STAGE FOR SUBSTANTIALLY MATCHING THE IMPEDANCE OF THE BASE-EMITTER CIRCUIT OF SAID FIRST STAGE TO THE IMPEDANCE OF SAID HIGH IMPEDANCE COIL AND INPUT CIRCUIT, A LOW IMPEDANCE CAPACITANCE-RESISTANCE CIRCUIT COMPRISING A SERIES CAPACITANCE AND SHUNT RESISTANCE COUPLING THE FIRST AND SECOND STAGES OF SAID MULTISTAGE CIRCUIT, SAID CAPACITANCE-RESISTANCE CIRCUIT HAVING A TIME CONSTANT SUBSTANTIALLY LONGER THAN SAID LONGEST PERIOD OF SAID PULSES, AND TRANSISTOR TRIGGER CIRCUIT MEANS HAVING A NORMAL CONDITION AS TO CONDUCTION, SAID TRIGGER CIRCUIT MEANS BEING COUPLED TO THE OUTPUT OF SAID MULTI-STAGE TRANSISTOR AMPLIFIER CIRCUIT TO BE OPERATED THEREBY TO REVERSE SAID CONDUCTION CONDITION TO PROVIDE A CONTROL OUTPUT IN RESPONSE TO THE AMPLIFIED SAID LOW FREQUENCY PULSE OUTPUT OF SAID COIL.