EKG Shield - signal path

[danvol23]

Hello,

I bought Olimex EKG Shield and I managed some measurement of the path which the signal goes through the board according to the schematic in the datasheet. It was done because it seems to me that the signal is still very noisy at the output. With the oscilloscope, I discovered that the signal firstly appears on the C9. How does the signal go for example through the instrumental amplifier or the gain after that when the R30 and R31 are missing. Through the V_REF? I do not really understand it. Should I add some components? The signal still has the baseline wander at the output as well. If you could describe to me this, I would be grateful.

Thank you,
Daniel

[LubOlimex]

R30 and R31 are not missing, these are board mounted meaning there is connection (short-circuit between the pads).

This is done so that you can place additional low pass filter if you decide (using the pads for resistors R30 and R31 and C28 and C29 the capacitors - remember to cut the wire in R30 and R31 before solder placing anything over it).

[MarcusHue]

For which applications do you deem it reasonable to place a low-pass filter in this place?

Thanks for your help!

[LubOlimex]

When the power supply or the environment are very "noisy" and input high frequencies into the readings. The logic behind the low pass filter on the operational amplifier is well explained here:

https://www.electronics-notes.com/articles/analogue_circuits/operational-amplifier-op-amp/low-pass-active-filter.php