Hello,
I am currently beginning to design/brainstorm for a 20 channel (differential bio-amps) for an EEG cap and read the data in matlab in real-time/post analysis via SD card, Ive built and designed bio-amps before and just hooked them up to a microcontroller since I only needed maybe 3-8 ADC channels, but never of this magnitude.

So I was wondering if using an analog multiplexer and hooking this up to a microcontroller adc channel and reading data in matlab or saving to SD card for post analysis. I would like a comfy 1kHz sample rate per channel, so 20kHz overall. And if simultaneous or sequential would be better? Sequental seems fine to me, but this is new to me so....

If you have any suggestions, thatd be great. If I should even use an analog multiplexer...

Thanks

 

If you can live with sequential acquisition then using a multiplexer would be a simpler solution.
20 channels is an odd number. The number of channels is usually a power of 2, for example, 8, 16, 32, etc.

https://www.vishay.com/docs/65150/dg506b.pdf

 

Hello,
I am currently beginning to design/brainstorm for a 20 channel (differential bio-amps) for an EEG cap and read the data in matlab in real-time/post analysis via SD card, Ive built and designed bio-amps before and just hooked them up to a microcontroller since I only needed maybe 3-8 ADC channels, but never of this magnitude.

So I was wondering if using an analog multiplexer and hooking this up to a microcontroller adc channel and reading data in matlab or saving to SD card for post analysis. I would like a comfy 1kHz sample rate per channel, so 20kHz overall. And if simultaneous or sequential would be better? Sequental seems fine to me, but this is new to me so....

If you have any suggestions, thatd be great. If I should even use an analog multiplexer...

Thanks

is this just for yourself , or for medical usage?
are you selling this?

are these signals at a reasonable level by the time you want to sample them, or still eeg levels ?

there are also chips and evaluation boards available, adds with built in mux,

https://www.analog.com/en/solutions/healthcare/vital-signs-measurements/eeg-measurement.html

 

is this just for yourself , or for medical usage?
are you selling this?

are these signals at a reasonable level by the time you want to sample them, or still eeg levels ?

there are also chips and evaluation boards available, adds with built in mux,

https://www.analog.com/en/solutions/healthcare/vital-signs-measurements/eeg-measurement.html

This is just for me, be a fun project. The levels(guessing you mean voltage) of the signal will be amplified before sampling, they wont be the base mV range. If this is what your asking.

And thanks i'll look into this.

 

If you can live with sequential acquisition then using a multiplexer would be a simpler solution.
20 channels is an odd number. The number of channels is usually a power of 2, for example, 8, 16, 32, etc.

https://www.vishay.com/docs/65150/dg506b.pdf

Im still on the fence for sequential, a delay depending on how long would be an issue. Still researching. And the 20 channel is bc the EEG cap I was looking to purchase has 20 electrode positions.

 

Im still on the fence for sequential, a delay depending on how long would be an issue. Still researching. And the 20 channel is bc the EEG cap I was looking to purchase has 20 electrode positions.

Each time the analog mux switches , it will introduce an error .
Think in terms of the charge needed to get all that capacitance up the the new voltage .
So in each switch , you have an inherent settling time till you can read a good sample.
This is different to the bandwidth of the mux.
Thus it's easier to get consistent results if you switch infrequently.
The adc with built in mux are better than using an external mux, as they have much better controlled impedances etc.
The kicker , is the DC . Your only interested in the AC , but each sencor / amplifier will have a different DC offset that you need to cancel out at the only to the adc. Else wise the input overloads / clips.
Btw. you probably need to remove some DC / base wander in your samples , post processing .
If it's just for fun , an analog mux , with post processing is going to be fine.
The sort of gear I've been involved with , is moving to a more digital solution , using sigma delta ADC , one for each Chanel , with active DC feedback / clamping , and uses fft post processing ..
What amplifiers are you using for the helmet ? How are they powered ? What have you done for esd and common mode voltage neutralisation ?

 

Each time the analog mux switches , it will introduce an error .
Think in terms of the charge needed to get all that capacitance up the the new voltage .
So in each switch , you have an inherent settling time till you can read a good sample.
This is different to the bandwidth of the mux.
Thus it's easier to get consistent results if you switch infrequently.
The adc with built in mux are better than using an external mux, as they have much better controlled impedances etc.
The kicker , is the DC . Your only interested in the AC , but each sencor / amplifier will have a different DC offset that you need to cancel out at the only to the adc. Else wise the input overloads / clips.
Btw. you probably need to remove some DC / base wander in your samples , post processing .
If it's just for fun , an analog mux , with post processing is going to be fine.
The sort of gear I've been involved with , is moving to a more digital solution , using sigma delta ADC , one for each Chanel , with active DC feedback / clamping , and uses fft post processing ..
What amplifiers are you using for the helmet ? How are they powered ? What have you done for esd and common mode voltage neutralisation ?

Thanks for reply.
Hrmm.. I need to read some datasheets, like how long before I switch for a good reading with a sequential,.Maybe just spend the money and get a good ADC with built-in mux or get a good DAQ for matlab to process with data aquisition toolbox. ANd skip the microcontroller setup altogether.
I was going to try and negate some DC offset with electrolytic cap at battery. And remove some in post with digital.
As for power haven't decided on what voltage of battery, but single-ended for amps with voltage divider.
I was looking at the AD623 in diff mode with a 2nd order butterworth, maybe with adjustable gains. I could just digitally filter the signals or amplify the signals with built-in gain, depending on what I use. But I have more then enough parts to build the filters, they're just collecting dust. Still brainstorming, but I appreciate the reply, thanks!