Open source EEG/ECG/EMG

Electrodes on the skin can be used to measure muscle (electromyography, EMG) brain (electroencephalography, EEG) and heart (electrocardiogram, ECG/EKG) activity. These electrophysiological measures are popular for clinical, research and hobbyist applications (such as brain computer interfaces). Most commercial systems are “medical grade” – these expensive systems offer high precision (16-24 bits), participant electrical isolation as well as support. On the other hand, there are numerous “hobby grade” solutions that are very inexpensive but do provide fewer features. Here we describe a “research grade” solution offering the same precision and safety of the medical systems, with the ability to add time stamps (for averaging data across trials) at a much lower cost (though without the FDA approval or support, so use these designs at your own risk).

Overview

This is an open source project for recording high quality electrophysiological data using an ADS129n compatible front-end. These chips support 4 (ADS1294), 6 (ADS1296) and 8 (ADS1298, ADS1299) channels for measurement with 24-bit precision (and if you need even more channels, you can daisy-chain multiple chips). The ADS communicates using a serial peripheral interface (SPI) link. In this design, an Arduino-compatible microcontroller translates between SPI and a Bluetooth or USB Serial Port Connection. Software in the Matlab and Processing languages allows a computer to record these serial port signals. The connection between the computer and the Arduino should be electrically isolated – either via a wireless bluetooth module (the JY-MCU sells for $8) or an electrically isolated USB connection (e.g. using an ADUM4160, $11).

One nice feature of the ADS129n is that they provide 24-bit precision. This allows a single hardware design to be used for very different applications (spanning EEG to ECG and EMG).

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