Circuit of Ultrasonic transducer sensor distance measurement device

 

The characteristic of this system is to use the single-chip microcomputer to control the transmission of ultrasonic waves and the timing of the round-trip time from the transmission of the ultrasonic waves to the receiving.Among them, only the wiring diagram of the front ranging circuit is drawn. The left and right ranging circuits are the same as the front ranging circuit, so they are omitted.

 

1. 40kHz pulse generation and ultrasonic emission

The ultrasonic transducer distance measurement in the ranging system adopts the piezoelectric ceramic sensor of UCM40, and its working voltage is a pulse signal of 40 kHz, which is generated by the single-chip microcomputer executing the following procedure.

puzel: mov 14h, #12h; ultrasonic emission lasts 200ms

here: cpl p1.0; output 40kHz square wave

nop;

nop;

nop;

djnz 14h, here;

ret

 

The input terminal of the front distance measuring circuit is connected to the P1.0 port of the single-chip microcomputer. After the above program is executed, the single-chip microcomputer outputs a 40kHz pulse signal at the P1.0 port, which is amplified by the transistor T,which drives the ultrasonic transmitter UCM40T, and emits 40kHz pulsed ultrasonic waves. And continue to transmit for 200ms. The input terminals of the right and left distance circuits are connected to P1.1 and P1.2 ports respectively, and the working principle of ultrasonic transducer distance

is the same as that of the front ranging circuit.

 

2. Reception and processing of ultrasonic waves

The receiving head adopts UCM40R paired with the transmitting head to convert the ultrasonic modulation pulse into an alternating voltage signal, which is amplified by the two poles of the operational amplifiers IC1A and IC1B and then added to IC2. IC2 is an audio decoding integrated block LM567 with a locking loop. The center frequency of the internal voltage-controlled oscillator f0=1/1.1R8C3, and the capacitor C4 determines its locking bandwidth. Adjusting R8 on the carrier frequency of the launch, then the input signal of LM567 is greater than 25mV, the 8 pin of the output end changes from high level to low level, as an interrupt request signal, sent to the microcontroller for processing.

 

The output of the front ranging circuit is connected to the INT0 port of the single-chip microcomputer. The interrupt priority is the highest. The output of the left and right ranging circuits of ultrasonic proximity transducer is connected to the INT1 port of the single-chip microcomputer through the output of the AND gate IC3A. At the same time, the single-chip P1.3 and P1.4 are connected to the input of the IC3A. At the end, the identification of the interrupt source is handled by the program query, and the priority of the interrupt is right then left.