The Design Of A Power Daption And FSK High Accuracy Ultrasonic Raging System Based On STM32 Microcontroller

Ultrasonic ranging is widely used in non-contact distance measurement field, such as liquid level detection, automatic robot navigation, vehicle safety driving assistance systems, offshore oil development, medical field and so on.Traditional ultrasonic ranging is based on the measurement of the ultrasonic flying time. However influenced by the inaccurate detection of the echo pulse edg、propagation attenuation、 ambient temperature、 ambient acoustic noise and other factors, the accuracy of ultrasonic distance measurement is limited to the millimeter.With a kinetic analysis about the ultrasonic generation、propagation and reception process, We design a power adaption and FSK (Frequency Shift Key) ultrasonic ranging system based on STM32 microprocessor in this paper. We use the transmitter to generate ultrasonic wave, whose frequency is switched from f1 to f2. And it aims to measure the ultrasonic ranging by detecting the moments when the frequency of the received ultrasonic signal is changing from f1 to f2.In order to eliminate the uncertainty of the receiving vibrator frequency switching time caused by the change of sound pressure at the relevant receiving point, we control the transmitting power of the the ultrasonic transducer in real time. As a result, we control the sound pressure at a constant value, then the frequency switching time is also controlled at a fixed value, by which the design overcomes the effects of inaccurate detection of the echo pulse edge, propagation attenuation and other factors on ultrasonic distance measurement accuracy.This paper will show you the design both the hardware and the software.In the hardware design, there are signal generator and adaptive power amplifier in the transmitting circuit. Also, the receiving circuit includes the amplification shaping circuit design, precision rectifier circuit and double limit comparator circuit. We select STM32 microcontroller to use its DMA logic functions and data capture processing in the purpose of real-time period acquisition of the received signal, in which the basic frequency can reach up to 72MHzby PLL frequency multiplier.In the software design, a high-precision detection algorithm is proposed to find the frequency switching point. Together with the cycle information collected by STM32, we can efficiently detect the frequency switching point position in the period gradient area. Then it ensures a high precision measurement of the ultrasonic flying time and distance.After an experiment, the results show that the measurement error of this system is less than 0.35mm, and the precision and stability are superior to traditional technologies.