EEG-SMT Scaling?

Started by Goldenspark, January 02, 2014, 12:48:03 pm

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Goldenspark

What is the overall gain of the EEG-SMT?

From the schematic I see an ADC reference of 4V, and gains of 12.36, 40 and 13 = 6427.2 total, which gives a full scale deflection of 622 uV (micro-volts) for an ADC count of 1024. Is that right?

I.e. the signals will be +/- 311 uV for +/- 512 counts?

LubOlimex

Hey Goldenspark,

The gain amplification theoretically (according to the schematic) is 12.36*13*101=16228.68 maximum. I can't say at what exact gain amplification the unit you received is set since we calibrate them according to a calibration signal but its gain can be adjusted easily via a trimmer.

Best regards,
Lub/OLIMEX
Technical support and documentation manager at Olimex

Goldenspark

Is there a standard for the gain on an EEG?
I see the various traces with 50uV or 150uV marked to show the pen scaling, but what would the full scale normally be?

I assume it must be something like +/-300uV or so to capture the large swing Delta waves etc.

All I know is that if I put a couple of electrodes on my forehead over the eyes, and swing my eyes from fully left to right, it saturates the input.

I guess I am going to have to check out the sensistivity myself by creating my own claibrator.
I presume I can do that with a low voltage AC source divided down with a resistive divider?