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I'm trying to find a cost effective method of taking samples of electrical signals of the body (and potentially plants).

Can you have one high precision instrumental amplifier and then use an analog mux to read different inputs (different electrodes on the scalp, chest)?

I looked at this mux (CD74HC4067). Is the on resistance a problem?

http://image.prntscr.com/image/100c8ac148e345bd9785fb0f418c6548.png

Do you have any other suggestions for a cheap EEG device?

Thank you for reading and best regards.

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For measuring biopotentials cheaply AND easily I would recommend using a dedicated analog front-end eg. ASD1194. One chip + some resistors and capacitors. All muxes, right-leg drive and ADCs are integrated, you just read your data over SPI.

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When reading really week analog signals, you'd very much try to avoid additional things in your signal path before you buffer/amplify that signal.

So, no, I don't think your analog multiplexer will do as is – you should have a high-input-impedance amplifier for every channel, and then you can mux all these amplified channels. Or don't – many microcontrollers come with an ADC that you can switch between different channels out of the box, or you just buy a multi-channel ADC.

At any rate, there's a lot of guides online on how to build your own EEG with e.g. an Arduino, a raspberry pi, other microcontrollers, DAQs…

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