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Ultrasonic ranging system design
Bradford(1993)
Publication title: Sensor Review. Bradford: 1993. Vol. 13
ABSTRACT：Ultrasonic ranging technology has wide using worth in many fields，such as the industrial locale，vehicle navigation and sonar engineering．Now it has been used in level measurement，self-guided autonomous vehicles, fieldwork robots automotive navigation，air and underwater target detection，identification，location and so on．So there is an important practicing meaning to learn the ranging theory and ways deeply. To improve the precision of the ultrasonic ranging system in hand，satisfy the request of the engineering personnel for the ranging precision，the bound and the usage，a portable ultrasonic ranging system based on the single chip processor was developed．
Keywords：Ultrasound r，Ranging System，Single Chip Processor
1.Introductive
With the development of science and technology, the improvement of people's standard of living, speeding up the development and construction of the city. urban drainage system have greatly developed their situation is constantly improving. However, due to historical reasons many unpredictable factors in the synthesis of her time, the city drainage system. In particular drainage system often lags behind urban construction. Therefore, there are often good building excavation has been building facilities to upgrade the drainage system phenomenon. It brought to the city sewage, and it is clear to the city sewage and drainage culvert in the sewage treatment system. comfort is very important to people's lives. Mobile robots designed to clear the drainage culvert and the automatic control system Free sewage culvert clear guarantee robot, the robot is designed to clear the culvert sewage to the core. Control System is the core component of the development of ultrasonic range finder. Therefore, it is very important to design a good ultrasonic range finder.
2.A principle of ultrasonic distance measurement
2.1 The principle of piezoelectric ultrasonic generator
Piezoelectric ultrasonic generator is the use of piezoelectric crystal resonators to work. Ultrasonic generator, the internal structure as shown, it has two piezoelectric chip and a
resonance plate. When it's two plus pulse signal, the frequency equal to the intrinsic piezoelectric oscillation frequency chip, the chip will happen piezoelectric resonance, and promote the development of plate vibration resonance, ultrasound is generated. Conversely, if the two are not inter-electrode voltage, when the board received ultrasonic resonance, it will be for vibration suppression of piezoelectric chip, the mechanical energy is converted to electrical signals, then it becomes the ultrasonic receiver.
The traditional way to determine the moment of the echo's arrival is based on thresholding the received signal with a fixed reference. The threshold is chosen well above the noise level, whereas the moment of arrival of an echo is defined as the first moment the echo signal surpasses that threshold. The intensity of an echo reflecting from an object strongly depends on the object's nature, size and distance from the sensor. Further, the time interval from the echo's starting point to the moment when it surpasses the threshold changes with the intensity of the echo. As a consequence, a considerable error may occur Even two echoes with different intensities arriving exactly at the same time will surpass the threshold at different moments. The stronger one will surpass the threshold earlier than the weaker, so it will be considered as belonging to a nearer object.
2.2 The principle of ultrasonic distance measurement
Ultrasonic transmitter in a direction to launch ultrasound, in the moment to launch the beginning of time at the same time, the spread of ultrasound in the air, obstacles on his way to return immediately, the ultrasonic reflected wave received by the receiver immediately stop the clock. Ultrasound in the air as the propagation velocity of 340m / s, according to the timer records the time t, we can calculate the distance between the launch distance barrier (s), that is: s = 340t / 2
3.Ultrasonic Ranging System for the Second Circuit Design
System is characterized by single-chip microcomputer to control the use of ultrasonic transmitter and ultrasonic receiver since the launch from time to time, single-chip selection of 8751, economic-to-use, and the chip has 4K of ROM, to facilitate programming. Circuit schematic diagram shown in Figure 2.
3.1 40 kHz ultrasonic pulse generated with the launch
Ranging system using the ultrasonic sensor of piezoelectric ceramic sensors UCM40, its operating voltage of the pulse signal is 40kHz, which by the single-chip implementation of the following procedures to generate.
puzel: mov 14h, # 12h; ultrasonic firing continued 200ms
here: cpl p1.0; output 40kHz square wave
nop;
nop;
nop;
djnz 14h, here;
Re
Ranging in front of single-chip termination circuit P1.0 input port, single chip implementation of the above procedure, the P1.0 port in a 40kHz pulse output signal, after amplification transistor T, the drive to launch the first ultrasonic UCM40T, issued 40kHz ultrasonic pulse, and the continued launch of 200ms. Ranging the right and the left side of the circuit, respectively, then input port P1.1 and P1.2, the working principle and circuit in front of the same location.
3.2 Reception and processing of ultrasonic
Used to receive the first launch of the first pair UCM40R, the ultrasonic pulse modulation signal into an alternating voltage, the op-amp amplification IC1A and after polarization IC1B to IC2. IC2 is locked loop with audio decoder chip LM567, internal voltage-controlled oscillator center frequency of f0 = 1/1.1R8C3, capacitor C4 determine their target bandwidth. R8-conditioning in the launch of the carrier frequency on the LM567 input signal is greater than 25mV, the output from the high jump 8 feet into a low-level, as interrupt request signals to the single-chip processing.
Ranging in front of single-chip termination circuit output port INT0 interrupt the highest priority, right or left location of the output circuit with output gate IC3A access INT1 port single-chip, while single-chip P1.3 and P1. 4 received input IC3A, interrupted by the process to identify the source of inquiry to deal with, interrupt priority level for the first left right after. Part of the source code is as follows:
receive1: push psw
push acc
clr ex1; related external interrupt 1
jnb p1.1, right; P1.1 pin to 0, ranging from right to interrupt service
routine circuit
jnb p1.2, left; P1.2 pin to 0, to the left ranging circuit interrupt service
routine
return: SETB EX1; open external interrupt 1
pop acc
pop psw
reti
right: ...; right location entrance circuit interrupt service routine
Ajmp Return
left: ...; left Ranging entrance circuit interrupt service routine
Ajmp Return
3.3 The calculation of ultrasonic propagation time
When you start firing at the same time start the single-chip circuitry within the timer T0, the use of timer counting function records the time and the launch of ultrasonic reflected wave received time. When you receive the ultrasonic reflected wave, the receiver circuit outputs a negative jump in the end of INT0 or INT1 interrupt request generates a signal, single-chip microcomputer in response to external interrupt request, the implementation of the external interrupt service subroutine, read the time difference, calculating the distance . Some of its source code is as follows:
RECEIVE0: PUSH PSW
PUSH ACC
CLR EX0; related external interrupt 0
MOV R7, TH0; read the time value
MOV R6, TL0
CLR C
MOV A, R6
SUBB A, # 0BBH; calculate the time difference
MOV 31H, A; storage results
MOV A, R7
SUBB A, # 3CH
MOV 30H, A
SETB EX0; open external interrupt 0
POP ACC
POP PSW
RETI
For a flat target, a distance measurement consists of two phases: a coarse measurement and.a fine measurement:
Step 1: Transmission of one pulse train to produce a simple ultrasonic wave.
Step 2: Changing the gain of both echo amplifiers according to equation , until the echo is detected.
Step 3: Detection of the amplitudes and zero-crossing times of both echoes.
Step 4: Setting the gains of both echo amplifiers to normalize the output at, say 3 volts.Setting the period of the next pulses according to the : period of echoes. Setting the time window according to the data of step 2.
Step 5: Sending two pulse trains to produce an interfered wave. Testing the zero-crossing times and amplitudes of the echoes. If phase inversion occurs in the echo, determine to otherwise calculate to by interpolation using the amplitudes near the trough. Derive t sub m1 and t sub m2 .
Step 6: Calculation of the distance y using equation .
4.The ultrasonic ranging system software design
Software is divided into two parts, the main program and interrupt service routine. Completion of the work of the main program is initialized, each sequence of ultrasonic transmitting and receiving control.
Interrupt service routines from time to time to complete three of the rotation direction of ultrasonic launch, the main external interrupt service subroutine to read the value of completion time, distance calculation, the results of the output and so on.
5.Conclusions
Required measuring range of 30cm ~ 200cm objects inside the plane to do a number of measurements found that the maximum error is 0.5cm, and good reproducibility. Single-chip design can be seen on the ultrasonic ranging system has a hardware structure is simple, reliable, small features such as measurement error. Therefore, it can be used not only for mobile robot can be used in other detection systems.
Thoughts: As for why the receiver do not have the transistor amplifier circuit, because the magnification well, integrated amplifier, but also with automatic gain control level,
magnification to 76dB, the center frequency is 38k to 40k, is exactly resonant ultrasonic sensors frequency
REFERENCES
1. Fox, J.D., Khuri-Yakub, B.T. and Kino, G.S., "High Frequency Acoustic Wave Measurement in Air", in Proceedings of IEEE 1983 Ultrasonic Symposium, October 31-2 November, 1983, Atlanta, GA, pp. 581-4.
2. Martin Abreu, J.M., Ceres, R. and Freire, T., "Ultrasonic Ranging: Envelope Analysis Gives Improved Accuracy", Sensor Review, Vol. 12 No. 1, 1992, pp. 17-21.
3. Parrilla, M., Anaya, J.J. and Fritsch, C., "Digital Signal Processing Techniques for High Accuracy Ultrasonic Range Measurements", IEEE Transactions: Instrumentation and Measurement, Vol. 40 No. 4, August 1991, pp. 759-63.
4. Canali, C., Cicco, G.D., Mortem, B., Prudenziati, M., and Taron, A., "A Temperature Compensated Ultrasonic Sensor Operating in Air for Distance and Proximity Measurement", IEEE Transaction on Industry Electronics, Vol. IE-29 No. 4, 1982, pp. 336-41.
5. Martin, J.M., Ceres, R., Calderon, L and Freire, T., "Ultrasonic Ranging Gets Thermal Correction", Sensor Review, Vol. 9 No. 3, 1989, pp. 153-5.
