The electronic board to replace the reference voltage on the earlobe for EEG measurement

An unstable reference point is a critical problem for electroencephalography (EEG) research since its instability introduces a significant distortion into the interpretation of the EEG signal. The main requirement for a reference point - electric potential should be unchanged. This is extremely difficult to implement in practice, due to biological processes occurring in the human body. Unlike other artifacts (network noise, electrical noise, blinking) that can be solved both by using analog circuitry (bandpass filters for noise, etc.) and by using various mathematical methods (method of head components for eye blink, etc.), a change in the potential of the reference point during the EEG measurement will be present in any case. Today, for a reference point an earlobe and overall average referential reference are used. The problems of using these methods are described in many works. In this manuscript, we propose a new method of using the reference point, electric potential which is generated by a 24-bit digital-to-analog converter (DAC). At the initial stage, a 24-bit analog-to-digital converter (ADC) reads the potential between the earlobes, and then on the STM 32 microcontroller through the DAC it generates such potential with an accuracy of 0.1 μV. From this moment, to calculate the voltage at the electrode, the voltage at the output of the DAC is used as the reference potential. Subsequently, the ADC makes comparisons of the potential between two points in the earlobes, which ideally should equal 0 V. In the case, if the difference between earlobes voltage is more than 0.1 μV, the DAC starts to compensate this value at its output, thereby averaging the value between the two earlobes. Algorithms in software to exclude instantaneous changes in potential on the earlobe were written in the STM32. Algorithms eliminate the uncontrolled effect of an increase of neuronal activity in the temporal region of the head. Thus, the developed prototype by DAC of the device replaces the potential on the earlobes and, based on mathematical calculations, provides a stable reference voltage for calculating the voltage on the electrodes.