Is My ECG Circuit Set Up Correctly with Virtual Ground and Electrodes?

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Discussion Overview

The discussion revolves around the setup of an ECG/EMG acquisition circuit, focusing on the use of active and passive electrodes, virtual ground creation, and the challenges faced in obtaining useful output signals from the circuit.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant describes their circuit setup using active and passive electrodes, a 5V supply, and a virtual ground at 2.5V.
  • Another participant expresses confusion about the use of a single supply and questions the appropriateness of the voltage levels being used.
  • A third participant clarifies that they are using a theoretical ground at 2.5V to create positive and negative voltage supplies.
  • A later reply notes that the specified voltage for the circuit is + and - 15V, suggesting that 2.5V may be insufficient and expressing uncertainty about the electrode circuit's subtleties.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correctness of the circuit setup, with multiple competing views regarding the voltage levels and the implications for the electrode circuit.

Contextual Notes

Limitations include potential misunderstandings about the electrode circuit's requirements and the implications of using a virtual ground at 2.5V instead of the specified voltage levels.

bour1992
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Hello, I am trying to make a simple ecg/emg acquisition circuit.

I am using 2 of these https://www.olimex.com/Products/EEG/Electrodes/EEG-AE/ active electrodes for the differential signal and this https://www.olimex.com/Products/EEG/Electrodes/EEG-PE/ as a passive DRL electrode.

My supply is the 5V output of a LM7805 and I create a virtual ground at 2.5V using the TLE2426.
This is what I have built in a breadborad.
I connect the output of the INA118 to an oscilloscope but nothing usefull is shown.

Do you see anything wrong in it?
 
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Sorry --- deleted my post after you replied. LOL

Actually, You are using it with a single supply in a weird way. I have no idea what will happen or what you are doing wrong. Sorry.
 
I am using a theoretical ground at 2.5V so that we have a positive voltage supply +2.5V and a negative -2.5V.
 
It's specified for + and - 15V, so I expect 2.5V is far too little.

I understand virtual ground. It's the subtleties of the electrode circuit I can't visualize. For example their Fig 9 shows gain to the RL electrode. I don't know enough about the signals to understand what your circuit might see differently.