BioSensorPlatform
Status: Abandoned. The pictured third revision did not work correctly and the earlier second revision was a BGA-based design. Also, the SATA cables turned out to be less than ideal.
If you are looking for an EEG development platform, the TI ADS1299EEGFE-PDK kit is ideal and widely available. Look into a USB-ISOlator board if it is to be used with a mains-powered computer. Consider the OpenBCI project for a complete EEG solution.
Design files are available in Open Formats for the KiCAD Open Source EDA Suite.
You can browse the design files or get the latest copy using Subversion:
svn checkout https://raw.githubusercontent.com/ha7ilm/opendous/master/Current_Designs/BioSensorPlatform/ opendous-BioSensorPlatform
The design uses powered electrodes connected with SATA shielded cables to reduce noise and provide low output impedance signals to the ADS1298. SATA cables are a cheap way to connect a differential signal pair, bipolar power supply, and ground through a shielded, controlled impedance and controlled capacitance commodity cable that is flexible and comes in lengths from 30cm to 1.5m. Also, SATA cables have lower capacitance than similarly sized coaxial cables and only slightly higher resistance. The Opennect-ADC-Differential connector pinout is used.
During exploration of non-contact electrodes the OpenLoop project pointed me towards this article. Based on those ideas the following amplified opamp-based electrode was designed:
The better the data the better the results so exploration of classic instrumentation amplifier electrodes is ongoing.
To improve common-mode interference a right leg driver circuit is required although for EEG this is usually placed on the neck.
A direct connection to the ADC is also useful.
