ECG circuit help

I have this circuit for recording 12-lead ecg in arduino. Whenever I record the augmented leads, especially aVR, its output graph is upright instead of the normal aVR which is downward. I also followed Wilson's Central Terminal but still the same. I am currently stuck with this and I need some help.

Picture of ECG circuit help
gmoon2 years ago

Invert output data of one axis mathematically, in the Arduino? I.E. (assuming your input is 1 byte) take the absolute value of (256 - data).

Your description is kinda sketchy, I think that's what you're asking...

OppaC (author)  gmoon2 years ago

Sorry, but that's not what I am asking. I think that by following wilson's concept, in this case connecting my left arm and left foot together with resistors and connect its' central terminal to the negative input of the instrumentation amplifier with the positive input connected to the right arm, the arduino should interpret its' signals via adc correctly. I am using a software that I interfaced it with the serial and plots the adc signals coming in the serial. Instead of the correct output graph of aVR, which is downward with the QRS complex pointing down, mine is upward.

gmoon OppaC2 years ago

Still don't get the distinction -- apparently your problem isn't with the data, it's with it's orientation on the display.

Flipping the data (or any other transformation, such as scaling to the output device) doesn't change the data, it merely formats. Back in the olden days of early computing (when people wrote their own screen display code), bitmap displays always flipped the Y axis. The origin was in the upper left, vs the mathematics convention of the lower left. But it's easy to correctly format with simple code.

RE: your schematic above. I suppose you could do this with the hardware by changing the last opamp stage to unity gain inverting (it's currently non-inverting)...

Or do I still not understand the issue?