Hardware circuit design of angle measuring instrument system using acceleration sensor

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In modern control systems, angle measuring devices are critical components that require high precision, and their measurement accuracy directly affects the performance and accuracy of the entire system. At present, the existing acceleration sensors are used to realize high-precision angle measurement, and mainly focus on single-axis angle measurement. This article will focus on hardware methods for achieving high-precision angle measurements using the ADXL202 dual-axis acceleration sensor.

This angle measuring instrument uses STM32F107 as the core chip for data processing. This is a low power, high speed 32-bit processor with a Cortex-M3 core. The angle measuring module uses a high-precision, low-power dual-axis accelerometer ADXL202, which can convert the acceleration signal into a digital square wave signal output, which can be directly connected to the STM32F107, and the current tilt angle can be calculated by a certain algorithm. The display module uses a 12864ZW type 128 & TImes; 64 dot matrix liquid crystal display.

Angle measurement module

The angle measurement module uses the low-cost, low-power, high-precision dual-axis accelerometer ADXL202 from Analog Devices, Inc., with a measurement range of -2g to +2g, which measures both dynamic acceleration and static acceleration. Its operating voltage is 3.0 ~ 5.25 V, the operating current is less than 0.6 mA, the highest frequency can reach 70 MHz, so in terms of power consumption, sensitivity and accuracy, choose ADXL202 as the core chip of the angle measurement module.

Figure ADXL202 functional block diagram

Angle measurement module hardware circuit design

In order to ensure the high precision and stable operation of the ADXL202, it is necessary to configure the signal period and the filter capacitor (determining the bandwidth of the signal) according to the chip technical documentation and actual use. The output signal of the ADXL202 is a pulse width duty cycle modulated signal, and the duty cycle T1/T2 is proportional to the measured acceleration. At 0g, the output is 50% duty cycle, and the sensitivity is 12.5% ​​of the pulse width duty cycle caused per g. Check the technical documentation of the chip, you can set the period of DCM through the resistor RSET: ADXL202 sets the bandwidth of ADXL202 through XFILT, YFILT external capacitor CX, CY, this bandwidth determines its measurement accuracy, and the capacitance CX, CY can go Aliasing and filtering. In order to minimize the error in the pulse width duty cycle, the analog bandwidth should be 1/10 lower than the pulse width duty cycle. Analyze the table 2 provided in the technical documentation, and consider setting the T2 to 1 ms and the pulse duty cycle frequency to 1 kHz. To meet the actual requirements and the minimum DCM error, select a filter capacitor of 0.05 μF. It is 100 Hz. According to the chip's pin configuration diagram and the above various configurations, the hardware circuit of the angle detection module can be designed. The circuit principle is shown in Figure 4. The pulse output terminal is directly connected to the I/O port of the STM32F107.

Angle acquisition schematic

As can be seen from the figure, the ADXL202 is a perfect biaxial acceleration measurement system based on a single integrated circuit. For the X and Y axes, the output loop converts the acceleration signal into a digital signal output with a pulse width duty cycle. These digital signals can be Directly transferred to the STM32F107, no A/D conversion or other additional circuitry is required.

This paper discusses the research and design method of a high-precision angle measuring instrument based on ADXL202. The angle measurement principle of ADXL202 and the input capture function of STM32F107 are introduced in detail. Through the experimental test, the measuring instrument can complete the angle measurement with high precision, and the reliability is good, which has positive significance for the research and design of the angle measurement.