Once again: Arduino + ECG = Lots of noise

Connection, ECG, EMG, EDA, etc.
MrFloppy
Posts: 10
Joined: Tue Oct 11, 2016 12:59 pm

Once again: Arduino + ECG = Lots of noise

Postby MrFloppy » Mon Oct 17, 2016 1:40 pm

Hi there,

i am having issues with the Bitalino ECG. I connected it to an Arduino, using a 3.7V 700mAh Battery to provide power to the breadboard. There's a cable from +(on the Breadboard) to Vin on the Arduino, and one from - to Gnd on the Arduino. For VSS I am using a voltage divider made of two 100kOhm Resistors. I put an analog highpass filter between vss and A3. This is where I pick up the signal and read it from the Arduino. The Arduino is connected to the USB Port of my iMac and sends data via Serial Bus.
I am using the Bitalino 3 lead electrode cable und reusable non-gelled electrodes. Placements for testing purposes is Ref:Right index finger, -:right middle finger, +:left index finger.
I have a very noisy signal, there even is a lot of noise when the electrodes are free of anything and not being moved. Any idea what i could do?

Here are the results:
Attachments
Bildschirmfoto 2016-10-17 um 3.24.55 PM Kopie.png
Raw data with no transfer function
Bildschirmfoto 2016-10-17 um 3.24.55 PM Kopie.png (243.03 KiB) Viewed 2287 times
Bildschirmfoto 2016-10-17 um 3.26.03 PM.png
With transfer function applied
Bildschirmfoto 2016-10-17 um 3.26.03 PM.png (130.22 KiB) Viewed 2287 times

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby BITalino » Mon Oct 17, 2016 1:45 pm

Hi there,

The noise source in your setup may be the USB connection to the computer if the computer is connected to the charger... please check the recommendations in the following thread: http://forum.bitalino.com/viewtopic.php?t=236

Best regards,
The BITalino Team

MrFloppy
Posts: 10
Joined: Tue Oct 11, 2016 12:59 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby MrFloppy » Mon Oct 17, 2016 2:34 pm

Hey there,

I tried to implement the advices that were given in this article. I even wrapped the cables and the sensor in paper and aluminium foil. I used a cable of 120 cm length. There is still noise in the signal. I know that there will always be some noise, so is this a reasonable amount of noise or do you see a chance to optimize my circuit?
Attachments
LaptopDistance.png
recorded via Laptop with a distance of 120 cm.
LaptopDistance.png (23 KiB) Viewed 2282 times

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby BITalino » Mon Oct 17, 2016 3:10 pm

The plot in this last picture shows indeed a reasonable amount of noise. Using our BITalino hardware base as ADC and transmitter generally we get better signals.

The main reasons for this are the battery operation, wireless transmission and regulated power supply to the sensors (independent from digital parts of the circuit such as the Bluetooth transmitter).

Nevertheless the signals you are obtaining now seem to be fairly manageable. If you run them through a digital filter on the receiver (either in real time or post processing) you can even reduce the noise further.

Best regards,
The BITalino Team

MrFloppy
Posts: 10
Joined: Tue Oct 11, 2016 12:59 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby MrFloppy » Tue Oct 25, 2016 3:12 pm

Thanks a lot for your answers. I could also get further improvements by changing the rc-component.

Now I have another question regarding the EDA sensor. I recorded some EDA data of two people watching the same youtube clip (https://www.youtube.com/watch?v=WyT0If4jRPI). I was expecting similar results but the data doesn't show much similarity. There is even a huge difference in the value range. Could please take a look and my data and tell me if this is typical EDA data or if I did something wrong?

Also, I have a data set where the value is below 0 in the beginning. Why is that?

Thanks a lot!
Attachments
EDAPart2.png
Participant 2
EDAPart2.png (18.65 KiB) Viewed 2194 times
EDAPart1.png
Participant 1
EDAPart1.png (25.53 KiB) Viewed 2194 times

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby BITalino » Tue Oct 25, 2016 9:46 pm

Glad to hear that our suggestions have worked out for the ECG. Regarding from the EDA plots it appears indeed to be a typical signal trace.

Note that the EDA greatly varies amongst people as each individual has differences in the way his/her sympathetic nervous system works.

Furthermore, the baseline is usually different as well due to skin moisture, temperature and other subject-specific factors.

As such, it is somehow expected that different users have different EDA profiles. You should seek relative measures like even amplitude, etc.

For in-depth information about this signal source, please refer to the following book: http://www.springer.com/us/book/9781461411253

As for the value below zero, further support will be provided. For now, please confirm that you're using the correct transfer function for your sensor:
http://bitalino.com/datasheets/REVOLUTION_EDA_Sensor_Datasheet.pdf
http://bitalino.com/datasheets/EDA_Sensor_Datasheet.pdf

Best regards,
The BITalino Team

MrFloppy
Posts: 10
Joined: Tue Oct 11, 2016 12:59 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby MrFloppy » Mon Oct 31, 2016 11:53 am

Thanks for your reply. You were right, I was using the transfer function for the wrong EDA sensor. Now I got rid of values below zero, thank you!

I faced another problem when using ECG and EDA together at the same time but I opened a new thread for this: viewtopic.php?f=12&t=412

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Once again: Arduino + ECG = Lots of noise

Postby BITalino » Wed Nov 02, 2016 2:35 pm

Glad to hear that one of the suggestions has worked out for you. We'll follow-up on the EDA issue shortly through the other thread that you have opened.

Best regards,
Hugo Silva


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