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　　Ultrasonic interference detector US0012 based on DSP and fuzzy logic technology

　　1Main features

　　US0012 is an ultrasonic interference detector signal processing dedicated integrated circuit made using CMOS technology. It has three major functions: interference detection, interference identification and interference alarm. Its main performance characteristics are as follows:

　　(1) Inner ultrasonic sending and receiving circuit, analog signal processor, digital signal processor (DSP), and bloggate technology (FUzz -Logictechniques, referred to as FLT), and multi -way alarm output circuit, adaptable Standard 40kHz ultrasonic sensor.

　　(2) It has the ability to adapt to natural conditions such as ambient temperature and does not require any adjustment when detecting interference inside the vehicle. In addition, the chip also has self-test and power-on reset functions. The US0012 device has ultrasonic detection standards solidified into the chip when it leaves the factory.

　　(3) The clock frequency can be set, and the chip can be equipped with a clock frequency of 40kHz or 400kHz. The chip can automatically adjust the sensitivity, or the sensitivity can be set by the user to adapt to different interferences and interference changes, thus eliminating the effects caused by changes in ambient temperature, power supply fluctuations and changes in the sensitivity of the ultrasonic sensor.

　　(4) There are 3 interference alarm output modes, namely LED signal output (can drive light-emitting diode alarm), main alarm output and auxiliary alarm output. It can automatically distinguish between weak interference, strong interference, blocking (the signal is blocked due to the open circuit of the ultrasonic sensor lead), and saturation (the receiver enters a saturated state because the echo signal is too strong), and sends out corresponding alarm signals.

　　(5) Using a +5V single power supply, the allowable power supply voltage range is +4.5V ~ +5.5V, and the power supply current is 0.65mA (typical value). The operating temperature range is -40℃~+85℃. 2 Pin functions and working principles

　　2.1 Pin function

　　The US0012 ultrasonic interference detector is packaged in DIP-20 or SOIC-20, and its pin arrangement is shown in Figure 1. The functions of each pin are as follows:

　　AUDD, AGND: are the analog power terminal and analog ground respectively;

　　UDD, GND: digital power supply terminal and digital ground;

　　RXGND? Shielded ground terminal. When designing a printed board, you should first wire AUDD and UDD, AGND and GND separately, and finally connect them together. All voltages inside the chip are based on GND;

　　TX1, TX2: two output terminals of 40kHz short pulse train;

　　OSCNNOOCOUT: They are the clock input terminal and the output terminal in order. They can be connected to 40kHz/400kHz quartz crystal or piezoelectric ceramic oscillator; an external clock can also be input from the OSCIN terminal. When inputting an external clock, the OS should be connected. The COUT terminal is left floating; Figure 2 CAP: The output terminal of the envelope detector should be connected to an external capacitor during design. The shielding end of the receiver should be connected to the RXGND end first, and then to the analog ground;

　　RX: Echo input terminal, the input AC voltage peak value is 0.1mV~10mV;

　　SEL40k: Clock frequency selection terminal. When this terminal is connected to high level, the 40kHz clock is selected, and when it is connected to low level, the 400kHz clock is selected;

　　ALEN: Alarm output control terminal. When ALEN is 0 (low level), ALARM is disabled, and the WARN and LED terminals output alarm signals at the same time;

　　ALARM: main alarm output terminal;

　　WARN: Auxiliary alarm output terminal;

　　LED: LED alarm driver end;

　　SENS1, SENS0: Sensitivity setting terminal, which can be used to set the sensitivity of the ultrasonic interference detector;

　　SAS: Adjust the sensitivity selection terminal. When SAS is 1, the sensitivity is automatically adjusted; when SAS is 0, the sensitivity is maintained at a fixed level. The sensitivity can be set in advance by the SENS1 and SENS0 terminals;

　　TP: Test/reset terminal. This terminal has an internal pull-up resistor. It will reset the chip when power is turned on. When this terminal is connected to low level, it can be used to test the chip.

　　2.2 Working principle

　　The internal circuit block diagram of the US0012 ultrasonic interference detector is shown in Figure 2. The device internally includes a clock oscillator, modulator/driver, preamplifier (A), 40kHz bandpass filter, programmable automatic gain control (AGC) amplifier, envelope detector, A/D converter, and control logic , digital signal processor (DSP), fuzzy logic phase detector (FLT) and multi-channel alarm. When the circuit is working, the 40kHz short pulse train output from the TX1 and TX2 terminals is first transmitted through the transmitter. When the receiver receives the echo inside the vehicle, the system sends the pulse train to the ultrasonic interference detector for analog signal conditioning. , and then converted into digital signals through the A/D converter and sent to DSP for digital signal processing. Finally, the FLT-based phase detector identifies the real interference from natural interference or other allowed interference and starts the corresponding alarm output. . The receiving end (RX) of the US0012 can accept an AC peak voltage of 0.1mV ~ 10mV, and the input impedance of this end is 200kΩ. US0012 adopts push-pull output driving mode, which can emit an ultrasonic pulse train in a short time of 0.6ms. The pulse peak-peak value can reach 10V, and the emission period is 44.4ms. Since the duty cycle of this pulse is very small, its average current should be very small. In fact, only 50μA of current is needed to generate an ultrasonic pulse train. The timing waveforms of pulse train and echo are shown in Figure 3. Leaving the TP terminal unconnected or adding a positive pulse to this terminal can complete the power-on reset function to initialize the chip. The clock frequency required by the US0012 ultrasonic interference detector can be generated by a crystal oscillator circuit or provided by a microprocessor.

　　The following is the working principle of the main unit circuit in the device.

　　(1) Analog signal conditioning circuit

　　The analog signal conditioning circuit includes a preamplifier, a 40kHz bandpass filter, an automatic gain control amplifier and an envelope controller. When the device works, it first pre-amplifies the received echo signal, then filters out the noise through a band-pass filter with a center frequency of 40kHz, and then passes the programmable AGC amplifier to keep the output signal at a fixed bias voltage. Finally, The envelope detector is used to extract echo information from it. During design, the CAP terminal needs to be connected to an external capacitor to maintain the output bias of the envelope detector.

　　(2) Digital signal processor and fuzzy logic phase detector

　　Since many external factors (e.g. lighting, air currents formed on the windshield or roof of the cabin, wind passing through the windows) can influence the emission and reception of ultrasonic waves inside the vehicle, to determine a real interference it is necessary to analyze the echoes Characteristic parameters in the waveform and the relationship between parameters are analyzed. In order to solve this technical problem, the US0012 ultrasonic interference detector specifically solidifies detection standards based on experimental data collected from many test sites. In order to meet the above detection standards, DSP should first be used to process the digitized echo, and then a fuzzy logic phase detector should be used to continuously check how these parameters change and the correlation between them, and finally determine whether the real echo is detected. interference. Figure 4 (3) Self-check

　　When power is first turned on, if SAS is 1, it will immediately enter the self-test mode to automatically check whether the chip is working normally, and at the same time check whether the power-on process is too slow and whether the clock signal on the OSCIN end causes an initialization error. Once an abnormality is found in the circuit, the system will output a low-level signal with a duration of 4.4s from the WRN end and the LED end respectively. Users only need to connect an LED to the LED terminal to observe the self-test results. After the fault was eliminated, the LED returned to normal flashing state.

　　(4) Sensitivity adjustment

　　Users can adjust the sensitivity of the ultrasonic interference detector according to different interference and vehicle operating conditions. Using the digital signals at SENS1 and SENS0 terminals to program the AGC, 4 different sensitivities can be selected, see Table 1 for details. Table 1 Sensitivity method settings

　　SENS1SENS0 sensitivity 11 high sensitivity 10 medium high sensitivity 01 medium low sensitivity 00 low sensitivity

　　(5) Automatically adjust sensitivity

　　The English abbreviation of automatic sensitivity adjustment is SAS (Self-Ad-justingSensitivity), which is a unique feature of the US0012 ultrasonic interference detector. It can automatically adjust reception interference or motion sensitivity according to current environmental conditions to eliminate the effects of ambient temperature changes, power supply fluctuations and ultrasonic sensor sensitivity. After power-on, if SAS is 1, it will first perform self-test. If SAS is still high after self-test, US0012 will enter the automatic sensitivity adjustment mode. Its adjustment process first starts with low gear sensitivity, and then automatically adjusts between low gear, mid-low gear, mid-high gear and high gear sensitivity according to external conditions.

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