Threshold indicator

Claim 1

THRESHOLD DETECTION APPARATUS FOR MONITORING A DIRECT CURRENT INPUT SIGNAL OF ANY AMPLITUDE BETWEEN PREDETERMINED POSITIVE AND NEGATIVE POTENTIALS, SAID APPARATUS COMPRISING: (A) A FIRST SCHMITT TRIGGER CIRCUIT INCLUDING A PAIR OF NPN TRANSISTORS, ONE OF THE NPN TRANSISTORS OF SAID TRIGGER CIRCUIT BEING NORMALLY ENERGIZED AND BEING DEENERGIZED WHEN A PREDETERMINED POSITIVE POTENTIAL IS APPLIED TO THE BASE OF THE OTHER NPN TRANSISTOR; (B) A FIRST INDICATOR DEVICE; (C) MEANS FOR COUPLING THE FIRST INDICATOR DEVICE TO THE COLLECTOR CIRCUIT OF THE SAID ONE NPN TRANSISTOR OF THE FIRST SCHMITT TRIGGER CIRCUIT; (D) A SECOND SCHMITT TRIGGER CIRCUIT INCLUDING A PAIR OF PNP TRANSISTORS, ONE OF THE PNP TRANSISTORS OF SAID SECOND TRIGGER CIRCUIT BEING NORMALLY ENERGIZED AND BEING DEENERGIZED WHEN A PREDETERMINED NEGATIVE POTENTIAL IS APPLIED TO THE BASE OF THE OTHER PNP TRANSISTOR; (E) A SECOND INDICATOR DEVICE; (F) MEANS FOR COUPLING THE SECOND INDICATOR DEVICE TO THE COLLECTOR CIRCUIT OF THE SAID ONE PNP TRANSISTOR OF THE SECOND SCHMITT TRIGGER CIRCUIT; (G) A POSITIVE D.C. POTNETIAL SOURCE; (H) A NEGATIVE D.C. POTNETIAL SOURCE; (I) A VOLTAGE DEVIDER NETWORK WHICH IS CONNECTED ACROSS SAID POSITIVE AND NEGATIVE POTENTIAL SOURCES AND WHICH INCLUDES A PAIR OF SERIES CONNECTED POTENTIONMETERS; (J) MEANS CONNECTING THE VARIABLE ARM OF THE OTHER POTENTIONMETERS TO THE BASE OF THE SAID OTHER NPN TRANSISTOR; (K) MEANS CONNECTING THE VARIABLE ARM OF THE OTHER POTENTIONMETER TO THE BASE OF THE SAID OTHER PNP TRANSISTOR; (L) AND MEANS COUPLING THE INPUT SIGNAL TO BE MONITORED TO THE JUNCTION OF THE SERIES CONNECTED POTENTIOMETERS.