| Electroencephalograph, as a window of human nervous activation, shows high value in clinical diagnosis, medical research and brain computer interface fields. While the popularity of EEG acquisition instrument available now is still limited due to its high-cost, poor portability and inflexibility in reengineering.The original EEG signal is extremely weak and easily to be disturbed by ambient noises, which is difficult in EEG acquisition. In this paper, the original EEG signal was enlarged thousands of times step by step with a three-stage amplifier. The instrumentation amplifier INA129 was used as the preamplifier for reducing the noise and improving CMRR. Since signal quality could be severely affected by a large number of high frequency noise and 50 Hz interference, the 100 Hz low pass filter and 50 Hz notch filter were applied to filter the noise. ADS8568 as an analog to digital converter could acquire 8-channel, 16-bit synchronously, multiple ADS8568 can be connected together in daisy-chain mode, making up the 32-channel analog to digital converter module. The digital part was based on STM32 microcontroller and the data could be either written on the SD card or transmitted via USB virtual serial port. The USB virtual serial port could ensure the transmission bandwidth and stability, it simplified the development of host program. After further digital filtered by MATLAB, the time-domain waveform and the frequency-domain waveform were displayed in the graphical user interface.The feasibility of whole system was essentially verified by testing hardware, software and the whole system after designing and manufacturing. |
