usually not many noise by Bluetooth to brain-duino board.

however depend on electrode contact condition this noise maybe increase.

this small noise will happened in case put Bluetooth interface to brain-duino.

Following shows how to reduce noise by Bluetooth interface.

cut VCC and GND connection of 4 PIN socket from brain-duino PCB.

then connect by two wire as following.

Bluetooth VCC to SJ1 L.

Bluetooth GND to C32 GND

this way we can eliminate noise from Bluetooth interface very nice.