UNO + EKG/EMG noise on Laptip charger on/off

[uudis]

Settings for Olimex EKG/EMG Shield:

Ref E      Closed
3V/5V      5V
AIN SEL    A5(1,2 Closed)
D4/D9      D9

Im getting lot of noise when reading data form USB while Laptop is charging.
When Laptop power supply are unplugged USB reading noise goes away and diagram gets clear readings.
On PC there is no chance on clear reading via USB.

Does someone get the same experience with USB cable connection?

[uudis]

I tied to cut USB cable +5 and GND wires off (and leave both data wires) and test while UNO powered from 7.5V/1000mA or 12V/500mA chargers. In all cases signal is full with noise, same as regular USB to PC connection.

So... might be DATA + and DATA - makes some interference ?

[LubOlimex]

This is normal. You can't filter the noise from the mains power supply completely.  There is a hardware filter that takes effect at 40Hz indeed, however the filter this filter has a 19.2dB rolloff per octave.

I recommend you to think of a software filter!

I also highly recommend you the document that we used as inspiration for the shied: http://openeeg.sourceforge.net/doc/modeeg/modeeg_design.html -
especially the part "A. Filter specifications" (of course, the EEG-EMG has higher cut-off frequency at 59Hz, which in SHIELD-EKG-EMG is 40Hz).

Best regards,
Lub/OLIMEX

[joe50]

Hi LubOlimex,

Do you have any idea how I could implement a 50Hz Notch Filter for my raw data from the shield? In ElectricGuru I have massive frequency peaks at 50Hz (presumably from background noise). I'd love to cut them out in the visual display.