A Real-Time Impedance Measurement System for EEG Based on Embedded System

Abstract

The contact between the electrodes in the electroencephalogram (EEG) machine and the scalp has a great influence on the quality of the EEG. In order to guarantee the quality of the collected brain waves, we designed an embedded real-time impedance measurement system for the EEG. The system uses the ADS1299 chip, which depends on the on-chip current source to generate an alternating current which is higher than the frequency of the EEG signal as the output signal for impedance measurement. After A/D conversion, the obtained signals contain both EEG signals and impedance measurement signals. Furthermore, the system uses stm32f723 as the main control chip to design a filter to separate the two kinds of signals, and calculate the impedance value between the electrode and scalp in real time. In this system, the EEG signal and the impedance value data are stored in the SD card in BDF format at the same time, which provides the basis for judging the effective EEG data in the later signal processing. At the same time, the impedance value is compared with the preset threshold, and the LED is used to indicate whether the scalp is in good contact. Based on stm32F723 embedded system, the whole system has high integration, small volume, high measurement accuracy and strong real-time performance, which is of great significance for obtaining high-quality EEG data.