Tachometer employing a motion sensing photocell connected as one arm of a bridge circuit

Claim 1

A SPEED-MEASURING APPATATUS, COMPRISING: A METER HAVING A CURRENT COIL AND A MOVABLE POINTER AND A CO-OPERATING SCALE CALIBRATED TO INDICATE SPEED UNITS, AND DEPENDING UPON THE FREQUENCY AND ENERGY CONTENT OF ENERGIZING PULSES SUPPLIED TO THE COIL; A BATTERY, A BATTERY CIRCUIT HAVING A PAIR OF BUSS LINES TO BE ENERGIZED FROM SAID BATTERY AS POSITIVE AND NEGATIVE BUSS LINES, AND A MANUALLY OPERABLE SWITCH TO CONNECT THE BATTERY TO SAID BATTERY CIRCUIT; A LAMP MANUALLY OPERABLE TO DIRECT AN INCIDENT LIGHT BEAM ONTO A MOVING OBJECT, TO BE REFLECTED BY AND FROM A SPECIFIC SELECTED AREA OF SAID MOVING OBJECT AS PERIODIC REFLECTED LIGHT PULSES; A LIGHT CELL TO RECEIVE AND BE ILLUMINATED BY SUCH REFLECTED PERIODIC LIGHT PULSES, AND SAID LIGHT CELL BEING CHARACTERIZED BY A HIGH RESISTANCE WHEN NOT ILLUMINATED AND BY A LOW RESISTANCE WHEN SO ILLUMINATED; A NORMALLY BALANCED WHEATSTONE BRIDGE ARRANGEMENT WITH FOUR IMPEDANCE ARMS CONNECTED TO SAID BATTERY CIRCUIT AND CONTAINING SAID CELL AS ONE ARM, AND HAVING TWO NORMAL BALANCE POINTS WITH A CAPACITOR CONNECTED BETWEEN SAID TWO BALANCE POINTS OF THE BRIDGE TO RECEIVE A CHARGE WHEN THE CELL IS ILLUMINATED AND THE BRIDGE THEREBY UNBALANCED; A SENSING FIRST TRANSISTOR CONNECTED TO AND ENERGIZED FROM SAID BATTERY CIRCUIT THROUGH ITS EMITTER AND COLLECTOR ELECTRODES; CIRCUIT MEANS CONNECTING THE WHEATSTONE BRIDGE CAPACITOR TO THE BASE ELECTRODE OF SAID SENSING TRANSISTOR, AND NORMALLY BIASING SAID SENSING TRANSISTOR TO OPEN CONDITION; A SWITCHING SECOND TRANSISTOR CONNECTED TO SAID BATTERY CIRCUIT THROUGH ITS EMITTER AND COLLECTOR ELECTRODES, AND MEANS NORMALLY BIASING SAID SECOND TRANSISTOR TO OPEN CONDITION; CIRCUIT MEANS INCLUDING A CAPACITOR AND A RESISTOR SERIALLY CONNECTING SAID SENSING FIRST TRANSISTOR COLLECTOR TERMINAL TO SAID SWITCHING SECOND TRANSISTOR BASE TERMINAL; AN OUTPUT PULSING THIRD TRANSISTOR CONNECTED TO SAID BATTERY CIRCUIT THROUGH ITS EMITTER AND COLLECTOR TERMINALS;