Currently I am trying to build a portable ECG device where by the ECG signal will then be sent to Arduino UNO where the data will be transmitted via Bluetooth and the waveform will be displayed on Android Phone. I've already built a circuit and have a good waveform. I also managed to successfully transmit the data via Bluetooth and gotten a signal displayed on the phone.
Here is the problem. I just found out (unfortunately) that Arduino UNO only reads from 0 - 5V. However, my signal range from -220mV to + 550mV. That being said, the signal that is being shown on the phone are clipped or only halved are shown and the negative waveform disappears. How do I shift the whole signal so that its value starts from above 0V ? I have tried non-inverting summing amplifier and it does not work, or maybe it was wrong placement to built. I have attached a schematics of my ECG circuit for references. I am supplying my circuit with 1x 9V battery where the power is split into +4.5V/-4.5V. I also have successfully built an analogue 50Hz notch filter. If anyone knows how to solve this, please share. Also, if I were to add summing amplifier, where should I add it ?
Take note, I have 2 signals that I am sending to the UNO. A0 Pin is receiving the filtered signal, and A1 Pin is receiving the unfiltered signal. Both signals need to be level shifted.
I am from a Mechanical background, so don't be too hard on me.
Newly Updated Schematic.