Circuit continuity or resistance tester having an audible output signal

Claim 1

A CONTINUITY OR RESISTANCE TESTING DEVICE COMPRISING A BATTERY-POWERED BLOCKING OSCILLATOR HAVING A FIRST RESISTOR AND A CAPACITOR THE DISCHARGE TIME OF WHICH CONTROLS THE FREQUENCY OF THE OSCILLATING OUTPUT CURRENT OF SAID OSCILLATOR, AN ELECTROMECHANICAL TRANSDUCER DRIVEN BY THE OSCILLATING OUTPUT CURRENT OF SAID OSCILLATOR FOR PRODUCING AN AUDIBLE SOUND HAVING A TONE RELATED TO THE FREQUENCY OF SAID OUTPUT CURRENT, SAID FIRST RESISTOR BEING PART OF A FIRST DISCHARGE CIRCUIT FOR SAID CAPACITOR, MEANS PROVIDING A SECOND DISCHARGE CIRCUIT FOR SAID CAPACITOR AND INCLUDING A TRANSISTOR, AND A BIASING CIRCUIT FOR SAID TRANSISTOR FOR VARYING THE RESISTANCE OF SAID TRANSISTOR IN SAID SECOND DISCHARGE CIRCUIT, SAID BIASING CIRCUIT HAVING TWO POINTS THE RESISTANCE BETWEEN WHICH TWO POINTS CONTROLS THE RESISTANCE OF SAID TRANSISTOR IN SAID SECOND DISCHARGE CIRCUIT, AND MEANS INCLUDING A SELECTOR SWITCH FOR SELECTIVELY CONNECTING AN EXTERNAL TEST CIRCUIT EITHER ACROSS SAID TWO POINTS OR IN PARALLEL WITH SAID FIRST RESISTOR.