A Design Of EEG Collecting System Based On DSP (Digital Signal Processor)

Electroencephalogram(EEG)signal is a typical signal of bioelectricity. When nerve cells of a brain transmit information, it is a general reflection of electrical activities in the cortical layer and on the scalp, which contains much physiological and pathological information. We can learn the relationship between the electrical activities of nerve cells and the physiological and pathological states of people, and this relationship has great significance in the province of the clinical medicine and the cognitive science. While people get a deeper acquaintanceship with the electrical activities of brains, a device that can note or describe electrical activities of brains is invented accordingly. An electroencephalograph is a device that specially does the job above. Along with the invention of differential amplifiers, the first electroencephalograph was invented in 1934. The operation theory of it is as follows: firstly, we can use electrodes that are placed in the cortical layer and on the scalp to detect low EEG signals. And then a connection of electrodes is used as a coupling to differential amplifiers, through which the EEG signal is magnified properly. Lastly, a recording device notes the signal.This paper mainly introduces the software and hardware design that we use in the technology research of EEG. And the analyses of EEG by are also introduced.In chapter one, we introduce the basic knowledge and classification of EEG at present, the fixing way of EEG electrodes and the connecting way of EEG. To study EEG better, it is necessary that it should be fully saved in a computer. From a different point of view, the hardware system is also a collecting system of EEG. We must magnify EEG because its voltage is very low, which is usually between 10uv and 50uv. In chapter two, we introduce the method to design the magnifying circuits in the EEG collecting system. Since the background noise of EEG is very strong, lots of disturbing signals are included in our measurements. So we also introduce an antijaming consideration and retraining measures of the eletrode lead.While magnifying EEG, polarizing voltage of electrodes, voltage of high frequencyinterference, voltage of 50Hz power line interference that disturbs EEG worst, are magnified at the same time. We must use filters to filter these interferers. So in chapter three, we introduce filter circuits used in EEG collecting system, including a low-pass filter, a high-pass filter and a 50Hz-trap filter. In chapter four, a controller is introduced. We choose TMS320VC5402 DSP as the controller of our system. Since the memory room of the chip is small, we extend a program memory and a data memory. To realize the task of sampling the EEG, we connect one multi-channel buffered serial port (McBSP) of DSP with a serial A/D converter TLV2544. We also use PC's parallel port to communicate with the host port interface (HPI) of DSP, and save the samples collected by DSP in the PC with the format of files. Detailed descriptions are also given upon the HPI and PC's parallel port.In the last chapter, we give detailed descriptions on the initialization of the system, on-line FLASH programming, communication program design of both DSP and PC, band-pass filtering, adaptive filtering and so on.Thus our system includes such steps as magnification, preprocess and A/D conversion of EEG, communication between DSP and PC, data preprocessing and saving. Surely these are the essential steps of the system debug. So this paper gives a relatively detailed explanation on both the hardware part and the software part.