SR1 and IC2A on EKG/EMG shield

[ellecieffe]

Hello,
please, could you briefly explain me the functioning of SR1 and IC2A blocks on the EKG/EMG shield?

Thanks

[ellecieffe]

Ok ... I've figured out the functioning of the two circuits.

The voltage reference (SR1) sets the voltage at its cathode by shunting the right amount of current through itself, causing a controlled voltage drop over R19, exactly 3V.

R22 and R23 divides the 3.0V in two, creating an unbuffered 1.5 volt reference for the VGND net.

After that it is buffered by IC2A (the part A of the dual op-amp IC2).

Now my (newbie) questions are:

1) Why you choose 3V for AREF and 1.5 for V_REF and not 3.3V for AREF (wiring AREF to 3.3V power pin) and 1.65V for V_REF?

2) Why do you need SR1 ? 3.3V is regulated by Arduino, not enough?


Thanks youuu