Why am I getting a "shark finn"-like signal?

AI Thread Summary
The discussion revolves around a team experiencing unexpected "shark fin" shaped spikes in the signal from their Arduino-based tapping device and pneumatic pump setup, which utilizes the triboelectric effect. Participants suggest that the observed pattern may be due to sampling aliasing, noise from USB communication, or grounding issues. They request additional details such as schematics, component datasheets, and oscilloscope readings to better diagnose the problem. One recommendation includes altering the resonant frequency by applying water to the triboelectric devices for further insights. The conversation emphasizes the need for more data to understand the signal anomalies effectively.
matteo_ianna
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Hello! My collegue and I are having hard time to understand what is happening. Basically we have a tapping device that work with Arduino and a pneumatic pump. The pump allows the tapping of two surfaces which perform triboelectric effect. We are connecting to those a logic analyzer (Seleae), to detect the signal and eventually quantifying the voltage produced. When we do it, we occour in this "shark finn" shape of the spikes, which pattern repeats all the time after n taps (see highlighted area in the picture). Do you have any idea why we are getting this pattern and no constant spikes?

Thank you so much in advance, really!

tribo problem.png
 
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Welcome to PF.

Ca you zoom in more on the signal? It may just be that you are getting some sampling aliasing in the displayed waveform.

Also, do you have a schematic and links to the datasheets for your components that you can share with us? Thanks.
 
matteo_ianna said:
logic analyzer
What does your (desktop) oscilloscope says?
What's your grounding setup?

Ps.: for me this looks like noise from regular USB communication.
 
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Is that trace of
1) one device
1) both of them electrically combined
2) both of the mechanically (acoustically) combined

Try putting a drop of water on one of the triboelectric devices to change its resonant frequency. That may well give clues to the cause.

Post the screen shot here so we can take some more wilda*s guesses.
 

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