Recieving bad quality EDA signal using Emotibit
aaltfer
Valencia
Hello,
In my research lab, we have acquired several EmotiBit sensors for studies involving human subjects. Initially, the EmotiBit EDA signals seemed to work fine, as shown in the example below:
In this image, the EDA signals exhibit good quality, with a visible tonic component and identifiable phasic peaks.
However, we have increasingly been registering poor quality signals, which mainly consist of noise or lack the expected tonic and phasic variations, as shown in the images below:
These images represent the raw EDA signals from different experiments. We have visually confirmed that data collection appears to be functioning correctly through the EmotiBit Oscilloscope.
Interestingly, we do occasionally register good quality signals, though this is inconsistent. Additionally, the EmotiBit sensors respond to movements in the bracelet or artificial manipulation, indicating that they are reading and transmitting data, but not reliably capturing physiological EDA responses.
In order to solve this bad quality EDA signal problem, we have tested several solutions, including:
• Changing the EmotiBit device (Two different Adafruit Feather M0 WiFi, and one Adafruit Feather ESP32 Huzzah).
• Replacing EmotiBit electrodes with new ones
• Updating and reinstalling EmotiBit software (versions 1.11.1, 1.8.4, 1.8.1)
• Measuring EDA signals from different individuals
• Adjusting the EmotiBit bracelet (tightening and loosening)
• Measuring EDA signals from different parts of the arm and hands
• Thoroughly cleaning the area where the EmotiBit is placed
• Trying to elicit high arousal and low arousal stimuli
• Using EmotiBit with low battery (30%, 10%) and high battery (70%, 90%)
• Directly feeding the EmotiBit with a power bank through the USB connection.
None of these attempts have resolved the issue.
Has anyone encountered this problem with EmotiBit? If so, were you able to resolve it, and what steps did you follow?
Comments
Hi, Aaltfer,
I notified our customer support staff and they may reach out either via email or here on the Forum. Mentioning @Shirley.
William
Hi @aaltfer,
Thanks for reaching out. Also, thank you for provided a detailed list of things you have tried.
Some questions to better assist you:
1. You mention you have several EmotiBits. Are you seeing this behavior on a single EmotiBit or all of them?
2. Regarding your comment on changing the EmotiBit device, do I understand it correctly that you tried different Feathers on the same EmotiBit that was showing this spurious noise?
3. While I don't suspect it, just asking to be thorough, was the EmotiBit connected to a host computer using a USB cable during these measurement? We don't recommend it since that creates a direct path for noise to enter the EmotiBit and it may causing the noise you are seeing.
4. Do you see similar instance of noise in other sensors, for example the PPG or IMU data?
Awaiting your response.
Best,
Nitin
Hi @nitin,
Thank you for your fast response.
1. We are seing this behavior in all tested EmotiBits (3 devices).
2. Among the 3 tested Emotibits, we have tried a total of 2 different Feathers.
3. We have tried to connect it directly through a USB cable once, with similar results. Nevertheless, our standard connection is through Wifi, with a UDP connection to recieve the data.
4. Other sensors such as PPG or IMU seem to be working correctly.
Hope these answers give you a more accurate picture of our testing methodology.
Best,
Alberto.
Hi Alberto,
Thanks for your response. It is definitely an interesting issue. We have never seen this before and we are trying to figure out how to help identify the problem. We have a list of possible root-causes but before we discuss them, I just wanted to touch on your comment about "occasionally getting good data". Can you share if in your experience, doing things a certain way leads to good data? If not, have you tried creating ideal conditions for collecting data, which would include:
If you can re-create near ideal conditions and test if you get good data, that could definitely provide more insight into how to solve any possible problem. Do note that I am suggesting "near ideal" conditions just for a test scenario because I'm interested to see if we can get good data with the best conditions possible. Once we establish the outcome, either way, we would have valuable knowledge to proceed with.
Regarding the possible root-causes, here are some things that can cause noisy data:
Relating to EmotiBit's contact with the skin
I noticed that all instances of bad data show the EDA at ~0.1uS, which indicates the skin resistance in the order of 10's of Mega Ohms. Although, this circuit should still not create noise at those resistance level, I'm interested to see if you have noticed the noise going away with the skin resistance going down due to sweat buildup. Additionally, note that applying lotion or having very cold or very dry skin will impact the EDA values, so just being aware of these things while testing may give additional insights.
Something in the Analog front end of the circuitry
This can include any abnormality from the snap sockets to the ADC (Analog to Digital Converter). These are very sensitive signals and can get affected by damage to any part of the board. For example, if the EmotiBit is strapped too tight causing the board to bend or flex beyond a stress point, it may damage the board which can lead to introduction of noise. Additionally, any flexion of the board can cause stress points along contacts where any IC is soldered to the board. Do you think excessive force may have caused damage to the board? This could also explain the spurious good data.
Issues with Power supply
The EmotiBit has independent supply ICs on board, that provide separate voltages for digital and analog sub-systems. It is unlikely that this is the cause, because every EmotiBit is tested in our factory and is shipped to customers only after passing a battery of tests. Also, your comments on other sensors working find and you getting intermittent "good data" go against this hypothesis. Additionally, all 3 EmotiBits showing noise makes it less likely that this is the issue.
On a high level, we are trying to figure out if it’s a hardware issue or something else. Since you can replicate it on all 3 EmotiBits, it looks unlikely that it is. If you can run a test with near ideal conditions and share your results & thoughts on if doing certain things mitigates the noise, we can get closer to a solution.
Waiting for your response on the questions above.
Thanks,
Nitin