Hi all,


I have a couple questions to ask about EEG circuits.


With the circuit below (from section 5 of the website), how do I calculate the resistor values (Rc,Rg,Re,R1,R2 and the unlabelled resistors for amps B and C)? Although the website is very informative it does not mention what the resistor values should be or how to calculate them. It just says that high quality resistors and transistors should be used.
Website: http://www.biosemi.com/publications/artikel4.htm

Next, how could this be extended to create a 32 channel device? The website mentions that two or four modules can be coupled to make a 16 or 32 channel system with one multiplexed output. But the multichannel design only measures two points, so wouldn’t four modules measure 8 point? I’m probably missing something here. Could someone explain what it means to couple four modules together.

 

Lucid.....Thank you for that link. I am by no means an expert in this field......but it sure explains why we get bio-senor questions......in a clear manner. Thanks.

As for your questions......it seems to me that the authors were using these discrete circuits to study a thick film process circuit for multi-channel applications.
If you are trying to use a multi-channel circuit.......please re-read the article.

In the first image...the transistor types are mentioned in the article. The resistor values for biasing the current sources will depend on the type of sensor/transducer you are using.......AND the frequency of desired signal.

The recommended op amps are also mentioned in the article also. The resistor and capacitor values for those depend on what gain you want and at what frequency the input potential is off.

That was most interesting about how a ionic fields react. Too bad there's not an easy solution to cancel it.

 

Lucid.....Thank you for that link. I am by no means an expert in this field......but it sure explains why we get bio-senor questions......in a clear manner. Thanks.

As for your questions......it seems to me that the authors were using these discrete circuits to study a thick film process circuit for multi-channel applications.
If you are trying to use a multi-channel circuit.......please re-read the article.

In the first image...the transistor types are mentioned in the article. The resistor values for biasing the current sources will depend on the type of sensor/transducer you are using.......AND the frequency of desired signal.

The recommended op amps are also mentioned in the article also. The resistor and capacitor values for those depend on what gain you want and at what frequency the input potential is off.

That was most interesting about how a ionic fields react. Too bad there's not an easy solution to cancel it.

Regarding frequency, I would like to measure delta to gamma waves, so anywhere from 0.1Hz to 100Hz. Or did you mean something else for the frequency of the desired signal. As for sensors, I plan on using silver-silver chloride electrodes (website below), but this may or may not change.

Electrodes: https://fri-fl-shop.com/product/tde-200/
Leads: https://fri-fl-shop.com/product/tde-207xx-lead-wire-for-disposable-eeg-electrode/

So with the frequency range and sensors, how exactly would I calculate the resistor values?

And thanks for mentioning the op-amps resistor and capacitors value, I forgot to ask! I’m not entirely sure what would be a good gain and what you mean by “at what frequency the input potential is off.” Could you clarify what you mean by that. For the gain, >20dB should work, that’s around what the article mentions.

And yea, I reread the article. I think it mentioned that it created an 8 channel module with the amplifier in the second picture, and this can be coupled with 4 modules to create a 32 channel system.

 

I wish I could, this is neat. I had no idea about this and it's interesting. I had no idea of the problems of detecting a bio signal.
Not quite sure of this sensor potential aspect.......so I probably mis-understood.

You know the first time they did this......they had to crack a skull open...don't yuh? ha ha

Have some patience. There are some experts on here who will know of these problems.
Some have built projects with very similar signals. I don't know the difference between delta and gamma.

I wish you success and look to follow your project progress. And welcome to AAC.

 

Thank you! And yea, I'll have some patience. I'm not in a rush to get this working, know it'll take plenty of time!