Ultrasonic distance measuring circuit for photographic camera - uses oscillator to discharge large value capacitor through step-up transformer to transducer for signal transmission

摘要

The arrangement includes a large value capacitor (3) charged from a battery (1) through a resistor (2). The capacitor is discharged in an oscillating manner into a step up transformer (4) whose primary (4a) is switched by a transistor (5) driven from an oscillator (7) when a button is pressed to activate the circuit. The transformer output drives the ultrasonic transducer (6). The reflected signal from an object (P) is applied to a gate (8) closed during the transmission period. The signal is amplified (9) and a circuit (10) compares the amplitude with a reference value. The output of the comparator and oscillator are applied to a counter (11) to determine the time interval between the time the oscillator commenced and the time when the comparator produced an output. This value is releated to the target object range.