Ultrasonic receiving circuit diagram

The ultrasonic receiving circuit diagram is shown below:

　　When ultrasonic waves propagate in the air, their energy will continue to attenuate as the distance increases. Through experimental measurements, when the detection distance is about 1m, the signal energy has attenuated to about 30mv. We need to amplify and filter the received weak ultrasonic sinusoidal signal and input it to the external interrupt port of the PIC as a sign of receiving the echo. The usual design idea is to first use an LM series amplifier for amplification, and then input it to INT0 to generate an interrupt through filtering, frequency locking and other circuits. The advantage of this method is that it can lock the required frequency to prevent interference from other frequencies of ultrasonic waves from the outside, but the disadvantage is that the integration is not high, and the design and welding are cumbersome. For this purpose, this paper adopts Sony's CX20106A infrared remote control receiver integrated chip, which can be used for ultrasonic processing circuits. It integrates functions such as amplification, limiting, bandpass filtering, peak detection, shaping and comparison, and has high sensitivity and anti-interference [5]. Pin 7 of the CX20106A chip is connected to the INT0 of the PIC microcontroller. When no ultrasonic wave is received, pin 7 outputs a high level of about 4.1V and no interruption occurs; when an ultrasonic wave that matches or is close to the center frequency of 40KHz is received, a low jump occurs.

　　When a bottom transition is detected, the first falling edge signal is input to INT0 as an external interrupt signal, then timer T1 is turned off and the count value of T1 is read to perform the next step of time and distance calculation.

　　Figure 1. System transmitting circuit diagram.