In the application of high-frequency ultrasonic data acquisition and frequency analysis, the system that receives the actual transmission is usually used to simulate the received signal. The most frequently used mode is the high-speed continuous sampling using the lower computer and the data analysis mode of the upper computer. Then, the detected signal is sent out through D/A. This mode can complete continuous sampling of M-level or even G-level data, and has been widely used in high-speed industrial signal acquisition.
The STM32-based real-time delivery system is proposed. The main control chip adopts the latest STM32F407 chip, which belongs to the latest generation of low-power high-performance system-on-chip launched by ARM. The core is CORTexM4, the highest frequency can reach 168MHz, and ARM is used internally. Reduced instruction set, single-cycle instruction, and integrated ARM's floating-point DSP instruction set, can perform signal filtering and FFT operation on data, computing power exceeds TI's 200M main frequency DSP; due to the use of system-on-chip design, the film It integrates a large number of peripherals and has strong control communication capability, which is very suitable for use in industrial control signal processing. The whole system is based on the low power consumption design of STM32, and the system is small in size. The whole system can work independently without relying on the host, which has a good application prospect.
2, system compositionThe STM32-based ultrasonic real-time transmission system is mainly composed of three parts: 1) signal conditioning; 2) data sampling analysis; 3) PWM emission composition. The overall hardware design is shown in Figure 1.
Figure 1 overall design
The system's core processor uses the STM32F407 chip based on the CORTexM4 core. The highest stable operating frequency is 168MHz, the core power consumption is only 128μA/MHz. It adopts ARM's 32bIT reduced instruction set, single-cycle instruction, and integrates ARM's floating. Point DSP instruction set, with multiply accumulator and divider, can perform signal filtering and FFT operation on data, with strong computing power, and can be compiled by open source ARM-gCC compiler, software design is more flexible, and STMicroelectronics The driver library has been written in the core and peripherals of the chip, which simplifies the application.
3, signal conditioning part of the designThe signal conditioning part uses the structure of the analog comparator input, and the structure is shown in Figure 2.
Figure 2 analog comparator input structure
The signal is passed through an analog comparator built by a high-speed op amp. The comparator's comparison voltage is provided by the STM32F407 DAC for initializing noise acquisition and threshold adaptation, which filters out noise present in the channel.
After the signal passes through the analog comparator, a standard square wave signal is obtained, and the square wave signal enters the IO port of the STM32F407.
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