To display the wave I am using XOSCILLO, a very cool and open source tool (which I wrote :P) that converts your Arduino into an oscilloscope.
Circuit diagram
Here is the scheme, I am using the typical instrumental amplifier(ins amp) and then another op amp to get some more gain. An ins-amp is like an op-amps but with a huge CMRR, I am using a AD8221 which comes in a tiny small package, it’s lead pitch is only 0.65mm, if you want to know what I did to create a simple breakout board please follow this link.
I’m using a single supply for the amps that comes from the arduino 5V pin, and I am creating a buffered virtual ground, this is really important.
Tricks of the trade:
This is what makes the difference between a working ECG and a non working one 🙂
The main problem is that the device is so sensitive that it get interference from almost everywhere, specially the mains hum at 50hz). As you can see I got a clean signal, and I am not using any kind of serious filtering, note that xoscillo has a low pass filter and I am not even using it, so what are the tricks?
Read More: Minimal ECG using an Arduino and Xoscillo