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

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The discussion focuses on the setup of an ECG/EMG acquisition circuit using active and passive electrodes. The user is utilizing a 5V supply from an LM7805 and creating a virtual ground at 2.5V with a TLE2426. However, they are experiencing issues with the output from the INA118 not displaying useful signals on an oscilloscope. Responses indicate that using a single supply with a virtual ground at 2.5V may be inadequate for the circuit's specifications, which typically require a higher voltage range. The conversation highlights the complexities of electrode circuit design and the importance of understanding signal gain and grounding in such applications.
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.
 

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