please help me in making Acusition sytem

[vjfaisal]

pic microcontroller eeg

hi


i wan to make my own Acusition system for EEG data, and it should be of 8 -channels. As EEG brain signal is in micro volts, so i have to use amplifire with higher gain.... uptill this know.......but

i want to know what should be the circuit, components,devices should be attach in its circuit diagram.

please help me if any one have some idea in it...........

best regards

 

[jamshid.dastur]

how many volts is an eeg signal

Well as per your requirement the best design implementation can be done by the use of OP-AMPS, as you have to obtain a very high gain to increase the milivolts to voltages of noticable value...after you've increased the level of voltages you can either use an Analog to Digital Convertor coupled with a microcontroller which would then present the data on some noticable media...the best solution will be to use a PIC Microcontroller as many of the PIC family has a builtin ADC to be used...
then the program of the microcontroller can be such that it presents your data on either a LCD Pannel or it would control some mechanical pen to graph it on the paper

 

[vjfaisal]

hi

ya i have done this.but at output donot get the good signal, because of noise...for that i have use the low pass filter, but still not clear .............

please give me the idea how to remove the noise 50 hz , and other small artifacts for the signal ,in the circuit so that i have the good signal.

regards

 

[sawaak]

Hi,
u can use a notch filter to remove the power noise of 50 HZ.



thanks
sawaak

 

[siavashhn]

Sorry my friend. but the correct dicttion is "acquisition". Good luck

 

[7rots51]

you can use TI 16 bit sigma delta ADCs that have internal 50/60Hz internal digital rejection filters

 

[andre_luis]

vjfaisal,

Digital filtering are preferable, due it adaptability, so you need choice microcontrolers with big amount of MIPS, like ARMs or DSPs.

It should be good to design a pre-amplifier close to patient head, in order to reduce the antenna effect of wire legh of probe cabling, taking needed signal conditioning.

That's all I remember, for while.

+++

 

[jamshid.dastur]

well as you are trying to get EEG Signals which are in real low milli volts, so while travelling from the EEG Strap to the rest of the circuit in between the enviroment produces a lot of noise over these small signals traveling through the cable, so when you try to amplify and filter the signals the noise is also amplified and filtered...the best solution will be that you first use some amplifier at the staps that is the strap should have some amplifier which would amplify the signal at the very initial and then send it to the cable ...in this way the signal will be more then just a few milli volts and later these large signals will be easier to be fitered and sorted out...so the model should be something like

strap->amplifier.........cable.........filter/controller/furthur amplifier/printer/etc

 

[vjfaisal]

hi jamshaid

kindly explain me what is starp ...........



regards

 

[jamshid.dastur]

Hi vjfaisalm
well as you're willing to make an EEG device which would get milli volts from the human body, so the electrodes of your device will definitely be connecting using some gripping tool, either a clip to grap the skin, or a stap which would cover your electrode, or a strap like the wrist watch or any other thing which would be connecting the electrode to the body...i was referring this connectivity medium as strap.
Best Regards

 

[vjfaisal]

hi jamshaid;

you have given me the good suggestion.......... but kindly tell me, are you giving me the following idea to implement


As EEg signal is in micro volts , the electrods itself amplify little bit, then from
i think that , strap , what i mean is the electroddes are attached to the Human Scalp with a special Gel.

1) electrodes (straps) > antialiasing low passfilter ( fc= 50hz) > ADC > Amplify ( 10k gain) > microcontroller > Pc

Is this right choice....... show me the clear sequence if any other ..........

2) As i want to work on some desired frequencies in the EEG signal coming from brain, there are also many other artifacts/interferance( EOG ,eye signals ) comeout from brain when we extracting signal( EEG) from brain. Can i implement the ANC filter at place just after extracing signal from Brain ,to subtract the those eye signals.

please help me ....its very imp

beat regards
Dj

 

[jamshid.dastur]

Hi VjFaisal, well yes by strap i meant electrodes + amplifier enclosed in the band to be attached, as closer the amplifier will be the lesser will be the losses...as you wanted to know about the workflow so check it out.
GEL<<<Electrode+amplifier<<<amplifier<<<output

well as you want to just filter out just the signals from the eyes while taking EEG of the brain, so as mmuch as i know is that brain generates different ranges of frequencies, well as i'm no doctor so i don't know which frequenct will the brain generate and which frequency would be of eyes, for this either you can consult a medial professional to ask about the frequencies, after knowing about the required frequency you may use the filter which you want, and yes this filter should also be located near the electrode amplifier for better result.

Do let me know if i've missed something to explain, or if you need some more explanations...Best of luck

Best Regards
Jamshid Dastur

 

[vjfaisal]

hi jamshaid;

you have given me the good suggestion.......... but kindly tell me, are you giving me the following idea to implement


As EEg signal is in micro volts , the electrods itself amplify little bit, then from
i think that , strap , what i mean is the electroddes are attached to the Human Scalp with a special Gel.

1) electrodes (straps) > antialiasing low passfilter ( fc= 50hz) > ADC > Amplify ( 10k gain) > microcontroller > Pc

Is this right choice....... show me the clear sequence if any other ..........

2) As i want to work on some desired frequencies in the EEG signal coming from brain, there are also many other artifacts/interferance( EOG ,eye signals ) comeout from brain when we extracting signal( EEG) from brain. Can i implement the ANC filter at place just after extracing signal from Brain ,to subtract the those eye signals.

please help me ....its very imp

beat regards
Dj