Help with EEG proyect

[spoke3000]

Hi:
I nned Help with a EEG project. The circuit used for the proyect is in this page http://openeeg.sourceforge.net/doc/.
The problem of the circuit is that teh signal output is only a nosie (50Hz) and the RLD (rigth leg driver) in not working properly.
Thank you....

 

[williB]

If you would link directly to the circuit , you may get some answers.

 

[spoke3000]

answer

what do you mean??

 

[audioguru]

I think the schematic and layout are in Eagle format and zipped.

 

[bmcculla]

Aluminum foil is great for getting rid of noise. Use it so sheild any unsheilded parts of the design. It will make a huge difference.

 

[Optikon]

Hi:
I nned Help with a EEG project. The circuit used for the proyect is in this page http://openeeg.sourceforge.net/doc/.
The problem of the circuit is that teh signal output is only a nosie (50Hz) and the RLD (rigth leg driver) in not working properly.
Thank you....

A comment: This circuit should not be posted & used if it obvioously hasn't been thoroughly tested for such noise problems.

One great place to check why you are getting so much 50Hz pickup from the power lines is in the PCB layout. Generally, big loops = big pickup. When you are trying to measure 10's of uV, it doesnt take much to ruin your day. One must focus on not picking it up & shielding against it in the first place. I'm not going to bother digging into the design for this kind of issue but it is a place to check for anyone interested.

The schematic also shows a 2 pole bessel notch filter in the signal path with a note that the center frequency is set at 59 Hz. Well this tells me that there is no concern about losing signal conent of interest at 59Hz. Being only 2 pole, it will give pretty lousy rejection of the 50Hz component that you are picking up. You could try changing the fc to 50Hz as best you can. Also my gut tells me that you should be using a little better than 5% components here to be able to more accurately place it at 50Hz. This filter only helps you with "normal" mode noise at this part of the signal path. It will do nothing for a common mode noise problem where the whole signal path is riding on the 50Hz referenced to somewhere else (presumably chassis, earth) You should investigate the source & pickup mechanisms of your noise problem a little further before thinking about how to solve them.

Just my .02

 

[audioguru]

Since the probes are connected to an unshielded patient and there are mains fields all around, the "right leg" connection is crutial to cancel mains hum.

Why doesn't the feed to the right leg work properly?
Please post the circuit with your voltage measurements of its opamp. :lol:

 

[spoke3000]

squemathic

The squematic of RLd id in the page
http://openeeg.sourceforge.net/doc/modeeg/modEEGamp-v1.0.png
The RLD is in the left of the page, between channel1 and 2.
Another thing, i change the last filter to Fc=49 Hz, and is not working (only noise of 50 Hz)......
Thanks