This web site is focused on sound card EEG hardware and software experimentation to create a Brain-to-Computer Interface (BCI). Two types of EEG units have been built to date, a dual channel AM unit and a dual channel FM unit. The FM unit uses approximately 4.5 kHz of audio spectrum per channel while the AM unit uses approximately 2 kHz of spectrum (with some guard band allocation) per channel.
The first attempt in building a prototype sound card EEG unit was begun in July 2005 . The first unit consisted of a two channel AM modulated version with a built-in power supply. It is compatible with 12-volt power cubes. There were several breadboards built before the final two boards (input amplifier and modulator) versions were completed. The AM version was successful with achieving about 65 dB of dynamic range performance. An existing oscilloscope software application was modified to accept the modulated signal from the prototype.
The second prototype was a single channel AM unit that reduced the modulation circuitry and the size of the unit was reduced to 2" by 4". The unit also included onboard regulators and was operated from a 9-volt battery. The unit design also switched from an analog local oscillator (LO) to a digital version (square wave oscillator). This reduced both the size and power consumption of the unit.
The third breadboard and then prototyped was a dual channel FM unit and due to reduced circuitry of implementing the FM modulation was built into the 2" by 4" enclosure with a 9-volt battery included. The total current drain is approximately 6.5 ma. The unit uses two CMOS digital local oscillators. The dual channel AM and FM units now achieve about 80 dB of dynamic range performance. Power drain is less than 6 ma.
New software application were developed specifically for EEG display and instrumentation. The software is able to receive data from both AM and FM units. The software incorporates individual channel gain and offset controls with a real time strip chart and vertical FFT displays. A built in variable bandwidth filter can be adjusted by moving cursor lines about the spectrum displays. A second software application interfaces to the NeuroServer. A third software package, BioSphere, provides biofeedback in the form of MIDI or Wave sounds along with the spectrum and waterfall displays. The fourth application, Keyboard2, is used with the eye cursor output screen of the BioShpere program. A 1.2 GHz Pentium computer is recommended for running the software applications. The main application screens are shown below:
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