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When analyzing the ultrasonic transmission characteristics, the energy of each cycle in the received signal is calculated based on the properties of the transmitted ultrasonic wave. It is assumed that the sine wave in each cycle is a standard waveform, and the transmitter’s vibrating plate has not yet reached a stable oscillation state. During the measurement process, if an object blocks the path of the ultrasonic wave traveling to the wall, the reflected signal from the wall becomes weaker. If the threshold is set too high, the wall echo might not be detected at all. Due to the irregular nature of the signal, a dynamic threshold is not reliable, so a fixed low threshold is used instead. The noise peak in the received signal remains relatively stable, and the fixed threshold is typically set to 3 to 5 times the noise peak.
Since the wall echo signal is constantly changing, the oscilloscope captures the signal during calibration, and the distance information is taken as 0.5 times the peak value of the received signal envelope (at n = 4 or 5). This processing method ensures that even when the received signal is too strong or too weak, the ranging error stays within 3 to 5 cm. However, if N is too large, the blind zone increases, and the measurement accuracy decreases.
The ultrasonic waves generated by the receiver's envelope head encounter echoes in various media, and the receiving head converts these echoes into electrical signals. When the ultrasonic wave hits the wall perpendicularly, the received signal envelope consists of two main phases: the start-up phase and the attenuation phase. Understanding this behavior helps in improving the reliability of the system during signal analysis.
The microcontroller series used in the system offers a wide range of analog and digital peripherals, along with multiple bus interfaces. It supports online programming and is widely used in many measurement and control systems. The microcontroller includes 5 timers, 5 PCA channels, and 4 ultrasonic sensor transmitters can share a 40kHz square wave for synchronized transmission. Meanwhile, 4 receiver heads can access 4 PCA channels. The signal amplifier circuit provides a gain of around 800. Even after passing through a band-pass filter, the noise peak can reach up to 30mV, which needs to be carefully managed to ensure accurate signal detection.
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