The STM32-based High Speed Data Acquisition System of Electrical Impedance Tomography

The data acquisition system aims to provide measurement voltages for EIT image reconstruction, so the speed and accuracy of system affect the quality and real-time of EIT image reconstruction. To address the issues of low transmission speed and data loss under high sampling rate in a serial I/O microcontroller, a new EIT data acquisition system incorporating DCMI (Digital Camera Interface) and DMA (Direct Memory Access) has been developed. The incorporation of a parallel interface DCMI enables high-speed data receiving from the ADC by the main controller STM32F4, while DMA optimizes data storage and retrieval, thereby enhancing the system's data transmission speed. Additionally, for the FFT-based digital demodulation we have derived the selection formulas of number of sampling points and proposed a pre-set input signal frequency method to ensure the integer-period sampling condition. The suggestions on parameter selection are beneficial to promptly determine the appropriate parameter to reduce the demodulation error. Experimental results show that this design greatly improves the data acquisition speed of system. This system can produce a sinusoidal excitation current with the frequency range of 1kHz to 1MHz, an output impedance of up to 525kΩ, and current stability below 1%. The measured voltages have good channel consistency, and the average SNR (Signal-to-Noise Ratio) of system can reach 64.5dB. The reconstructed image clearly identified the relative position of the placed target but also reveals some artifacts.