| 摘要 |
An ultrasonic detector for monitoring ultrasonic signals which have a selected ultrasonic frequency range and for producing an audible signal in response to the ultrasonic signals. The ultrasonic detector employs a sensor element which produces electrical signals in response to ultrasonic signals. Amplification and filter circuitry to remove all frequency components not within the selected range to produce a mixer input signal. An oscillator for producing a reference signal at a selected reference frequency. A mixer to receive the output of the filter circuitry and the oscillator to produce a mixed composite signal between 0 and 20 kHz and the composite signal amplitude corresponding to the input signal amplitude. The composite signal is passed through a low pass filter to produce a filtered composite signal. The filtered composite signal has a first component that is then amplified by a first amplifier to produce an audio signal which may be output to a suitable audio device. A second component of the filtered composite signal is amplified by a second amplifier, and a RSSI (Received Signal Strength Indicator) circuit is used to produce a strength indicator signal that may be displayed by a suitable visual display.
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