Status: Under Development. Third PCB revision has been prototyped. I'm scraping together funding for more development.

Opendous Inc. is currently developing an OpenHardware Biopotential Sensor Platform based on TI's ADS1298 ADC with ECG/EEG front end for use in a head-mounted 32+ non-contact electrode system.

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 http://opendous.googlecode.com/svn/trunk/Current_Designs/BioSensorPlatform/ opendous-BioSensorPlatform

Design

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.

Non-Contact Capacitive Electrode Example using OpAmp

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:

Non-Contact Capacitive Electrode Example using InAmp

The better the data the better the results so exploration of classic instrumentation amplifier electrodes is ongoing.

Non-Contact Capacitive Electrode Leg Driver

To improve common-mode interference a right leg driver circuit is required although for EEG this is usually placed on the neck.

Non-Contact Capacitive Electrode

A direct connection to the ADC is also useful.