by Forrest Sheng Bao http://fsbao.net
So here is the schematic of my ECG sampling circuit. I designed the circuit in fall 2010.
I would like to say that TI's(well, Burr-Brown's) instrumentation amplifier is awesome. You just put things together and then they rock. No need to tune the peripheral circuit. It's kinda like out-of-the-box solutions. Since the gain can be very high (10000 times linear), i think they can even be used for EEG sampling circuit.
I did not build the ADC circuit and interface to computers, but used NI myDAQ. The power supply for this circuit is also provided by NI myDAQ.
There are three electrodes connected to human body, the belly (ground), the left wrist (one input), and the right wrist (the other input).
This circuit can also sample signals output from NI myDAQ back to test the property of the circuit. Since the lowest resolution to NI myDAQ is 100mV, i used an op-amp (OPA177) as a voltage divider to scale down the output signal from NI myDAQ to its 1/10 (in voltage amplitude).
The schematic was drawn by gEDA/gschem. Click to enlarge.