Re: Lots of noise on the CH1 of my Olimex SMT?

Kris

There will always be 50/60Hz noise.  Except if you run from a battery
operated laptop, sitting in the desert, or similar.  What we have to figure
out is if the noise you see is "normal".

Firstly, the two channels must behave in a similar fashion, which they
don't.  The cause could be:
1. finger trouble (the way you connect the electrodes)
2. a connector/connection problem
3. a hardware problem on the SMT-EEG itself.

What you can rule out, is a USB/ USB cable problem, because then both
channels should behave in similar fashion.

Are you sure that channel 2 works?
Here is my hunch - the problem is with channel 2 and not channel 1 (!)

Let me explain.  Due to a number of different factors, channel 2 could
saturate (it clips against one of the DC power supply lines).  The ADC
would then read a constant 0-hex or 1023-hex value (saturated) and the
signal would appear as a flat-line with absolutely no noise.  To a newbie
this would appear correct.  It is not.  Only a QDS amplifier gives "0nV
noise" - but that is a joke you might not get, you would need to have read
this forum's posts of a few years back :-)

Check that you get some noise on channel 2, or connect channel 2 to the
square wave test voltage output (does SMT-EEG have that - I think/hope so,
too lazy to check on the schematic now).

A very simple test would be to connect CH1+ to CH1- to CH2+ to CH2_ to
DRL.  i.e. connect ALL 5 electrode wires together (bypass the physical
electrodes and your scalp for now).  You should then get two flat traces
with some low amplitude random noise.  This noise is the noise generated in
the instrumentation and opamp amplifiers.

If this test is successful, your SMT-EEG hardware should be fine.  Next I
would suggest you connect that build-in square wave test signal.  But that
in itself must be done correctly.  Baby steps first.

Bipolar amplifiers can be very confusing to newbies.  Your differential AND
common mode voltages must be within range.

Regards
Stefan

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