EEG Click Board™

Product Code: MIKROE-3359

What Is EEG? Electroencephalography (EEG) is a method used to record the electrical activity of the brain. This is a non-invasive method which uses a number of electrodes placed along the scalp. EEG measures voltage fluctuations which appear as a result of the ionic currents within the neurons of the brain. The measurement can be focused either on event-related potential changes (ERP) or on spectral content of the signal, collected during a certain period. EEG is most often used to diagnose epilepsy, which causes abnormal changes of EEG readings. HOW DOES IT WORK? The EEG Click Board™ is a single channel EEG monitoring device, based on the INA114, a precision instrumentation amplifier (IA) by Burr Brown®, a division of Texas Instruments, specialized in high-performance analog and mixed signal ICs. This IC offers a very low noise, LASER trimmed offset voltage, and very good common-mode rejection ratio. It uses a single resistor to set up its gain, which can easily be set up to 10,000.

On this Click board™, the INA114 IA has its gain set to about 12 times. Further amplification and signal filtering is done by the MCP609, a four-channel op-amp from Microchip, so that the final gain factor is about 7800 times. Such high amplification is necessary in order to amplify very faint voltages generated during the brain activity. To fine-tune the amplification, there is a multi-turn precision potentiometer which allows to set the gain of the intermediate amplification stage between 10 and 100 times. Since the "brain waves " can be both positive and negative, EEG click uses a virtual GND at the potential of 2.048V. This also helps reducing the noise from the common GND, improving the readings quality. The amplified brain activity signal is available at the AN pin of the mikroBUS™, allowing sampling by the host MCU. EEG measurements should be ideally conducted in an electrically isolated room, since any type of electromagnetic interference (EMI) could corrupt the measurement data. However, the INA114 offers some EMI protection, as it features an extremely good common-mode rejection ratio (CMRR), allowing to successfully cancel out most of induced interferences. The EEG Click Board™ uses 3-electrode setup, which can be connected over a 3.5mm Jack connector on the Click board™. Although the best results can be achieved by using silver-chlorine plated electrodes, any type of electrodes can be used. EEG uses the DRL electrode placement scheme: two electrodes are placed behind the ears, while the third electrode is placed on the forehead. The DRL electrode (on the forehead) helps eliminating the common voltage, while two other electrodes are connected to the differential inputs of the INA114 IA. The complete signal path is very well protected against voltage spikes and transients, that might appear as a result of the electrostatic discharge (ESD) in contact with the human body, so there is a set of ESD suppressing diodes and TVS diodes, which prevent sensitive IA and operational amplifiers on its output to become damaged by ESD events. SPECIFICATIONS Type Biometrics Applications The EEG Click Board™ can be used in EEG biofeedback mental training, for experimentation and development of brain-machine interface applications, or for simple monitoring of the brain activity. On-board modules INA114, a precision instrumentation amplifier (IA) by Texas Instruments; MCP609, a four-channel operational amplifier from Microchip; MAX6106, a 2.048V reference from Maxim Integrated. Key Features ESD and EMI protection of the inputs, compatible with several types of electrodes, high-precision instrumentation amplifier with high CMRR, gain regulation, etc. Interface Analog Compatibility mikroBUS Click board size L (57.15 x 25.4 mm) Input Voltage 5V PINOUT DIAGRAM This table shows how the pinout on the EEG Click Board™ corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns). Notes Pin Pin Notes EEG signal OUT AN 1 AN PWM 16 NC NC 2 RST INT 15 NC NC 3 CS RX 14 NC NC 4 SCK TX 13 NC NC 5 MISO SCL 12 NC