Piezoelectric ultrasonic apparatus and method for determining the distance from a predetermined point to a target

DETAILED DESCRIPTION The invention comprises apparatus and method for determining the distance from a preselected point to a target.
The apparatus directs an ultrasonic signal from a piezoelectric transducer at a preselected point toward the target, receives a reflection signal back from the target, and converts the time delay into the corresponding distance causing the time delay.
A circuit actuated by the receiver produces a linear, temperature-corrected voltage which is proportional to the distance of a target from the piezoelectric transducer.
The circuit can be broken down into three sub-circuits: (1) an input interface circuit, (2) a counter and multiplying digital-to-analog converter circuit, and (3) a temperature measurement and compensator circuit.
In the first circuit the analog output from the transceiver is inverted by an A.
C.
coupled amplifier, and the output is fed to one input of a comparator.
The other input to the comparator has a D.
C.
voltage which sets the threshold level which the return echo must exceed before an output pulse is produced.
A trigger output from the transceiver is fed to two one-shot multivibrators in series.
The first one disables the detector during the time the transducer is ringing from the transmit pulse.
The second one produces a positive pulse during which a valid echo may be detected.
The output signal from the second one-shot multivibrator and the output from the comparator are then fed to an AND gate.
When an echo is present during this time window, a positive pulse is generated by the AND gate to drive another one-shot multivibrator which generates a carry-out pulse, so that only the first echo is detected in each transmit/receive cycle.
In the second circuit, clock pulses are generated and a signal fed to three, four-bit binary counters wired in series and connected to two hex "D" type flip-flops.
The outputs from the flip-flops go to the inputs on a multiplying digital-to-analog converter.
An operational amplifier provides the analog output