EEG preamplifier for the USBDUX-sigma

Assembly of the circuit

eeg-1.0.zip contains the EAGLE files and the BOM. We do not provide the PCB but it can be ordered from Beta Layout by sending them the .brd file. They can also fit the components. All components can be ordered from Farnell. Simply copy and paste the BOM into their "quick paste" order form.

Description

The amplifier operates at a gain of G=2000 (G=500). If you have an EEG of approx 100uV you'll get 200mVp-p at the A/D converter. The USBDUX-sigma has an input range of +/- 1.25V so that there is enough headroom to accommodate baseline shifts due to cable movements and DC drift. The lower gain (G=500) setting can be used for testing, for example recording an ECG or an EMG. A simple low pass at 0.1Hz filters out electrode drift.

Recording instructions

Here are two recording scenarios. One for recording EEG during sleep (or anaesthesia) and one for visually evoked potentials where a stimulus is presented many times.

To record an EEG connect three electrode cables to the pins which are labelled "+,-,GND".

It is important to place the electrodes on skin with little or no muscles underneath.

Sleep EEG

+	right forehead
-	right cheekbone
GND	left cheekbone

To record the EEG use the program comedirecord.

Visually evoked potentials

+	over visual cortex back of the head
-	right cheekbone
GND	left cheekbone

Software:

To generate the checkerboard stimulus use Physio Stim.
To average the stimuli use Physio PSTH. For this purpose switch on linear averaging.

VEP of a 4Hz checkerboard stimulus: