A DIY ECG made from single op-amp (LM741) and 5 resistors by Scott Harden:
I made surprisingly good ECG from a single op-amp and 5 resistors! An ECG (electrocardiograph, sometimes called EKG) is a graph of the electrical potential your heart produces as it beats. Seven years ago I posted DIY ECG Machine on the Cheap which showed a discernible ECG I obtained using an op-amp, two resistors, and a capacitor outputting to a PC sound card’s microphone input.
DIY ECG with 1 op-amp – [Link]