NodeMCU <-------> AD8232
3.3V <-------> 3.3V
Gnd <-------> Gnd
D5 <-------> LO+
D6 <-------> LO-
A0 <-------> Output
One of the problems was that the green and yellow wires were swapped.
RED: Rigth Arm
GREEN: Left Arm
YELLOW: Rigth Leg
I've seen a lot of example code for the NodeMCU board that reads the analog output of the AD8232 circuit.
Even so, I couldn't get a clean ECG.
So here's the code I've developed implementing all the lessons learned in the way.
In summary, NodeMCU creates an AP and a web server that displays an interface that receives data from the NodeMCU via websocket; the main page's JavaScript code receives, processes, and displays the data, both in the time domain and a fast FFT showing the frequency domain.
A button for downloading data to a csv file added.