Problem with TI's ECG front-end

Thread Starter

filo123

Joined Jun 4, 2012
1
Hello,
I am building a simple 3-lead ECG for a university project and I don't get the desired ECG signal. I started with a reference front-end from TI (paper SLYT226) that looks like:


My circuit:

the only not exact components are R4 R5 (40,2k instead of 40k) and R9 (22k instead of 20k).

The circuit is built on a two sided PCB, all traces kept short, resistors and capacitors 0805 SMD 1%, both ground and power planes, at least one 100n cap at every chip. I tried powering it with 5V both from batteries and USB (I know.... noise).
That what the layout looks like (I omitted GP&PP for clarity):


That is my output TP1:

When I "zoom in" I see only 50Hz spikes.

That is the signal from INA326 (TP2):

The lower envelope is my ECG signal.

And the signal from the integrator output (TP4):



The ECG leads are about 35cm long (single wire). I use commercial 3M electrodes (I get about 300k chest resistance measured with a multimeter).
What am I doing wrong? Or is something known wrong with this reference front-end?
Thank you for your answers.
 
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