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Topic: Processing 2 Analogue Inputs To Create Differential Value (Read 4438 times) previous topic - next topic


Old post revived.

Arduino can measure +/-5volt with a normal 2-resistor voltage divider, e.g. 10k:10k.
The resistor that is normally connected to ground is now connected to 5volt.
That gives 2.5volt on the divider with 0volt input (value ~512).


You'll need an instrumentation amplifier to measure the difference in potential between two electrodes. The REF pin of the IA can be tied to 2.5V so that you can handle both positive and negative inputs.

50Hz or 60Hz mains interference may be a problem, unless you run everything from batteries and go to the middle of a field to take readings.. You will probably need to follow the IA with a notch filter to remove this, and then an op amp to provide further amplification before the signal is large enough for an Arduino to digitize.
Not so true and overkill, if proper grounding techniques are observed and implemented IE; no daisy chains or ground loops, also if you have "box" or faraday shielding, only one end of the shielded cable need be grounded to the case.

However, you should consider the safety aspects. What would happen if the Arduino was being powered from USB, and the computer developed an earth fault? Medical EEG equipment has a high degree of isolation between the electrode amplifier module and the rest of the equipment, so as to be safe in the event of an equipment fault.
A good idea and design practice. Running from a USB phone recharge pack will work well, just observe that they usually time-out if there isn't enough current draw (> ~ 200mA)
Electronics Engineering student - "E=MC^(OMG x WTF?!)"
Professional Auto Collision/Custom tech

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