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

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Discussion Overview

The discussion centers around the unexpected "shark fin" signal pattern observed when using a tapping device connected to an Arduino and a pneumatic pump, which is intended to produce a triboelectric effect. Participants are exploring the nature of the signal captured by a logic analyzer and seeking to understand the reasons behind the observed waveform characteristics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that the "shark fin" pattern may be due to sampling aliasing in the displayed waveform and requests a zoomed-in view of the signal.
  • Another participant inquires about the readings from a desktop oscilloscope and the grounding setup, proposing that the observed pattern might be noise from regular USB communication.
  • A different participant asks for clarification on whether the signal trace is from one device, both devices electrically combined, or both combined mechanically, and suggests experimenting with a drop of water on one of the triboelectric devices to alter its resonant frequency for further insights.
  • There is a request for a screenshot of the signal to facilitate more informed guesses about the issue.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the cause of the "shark fin" signal pattern, and multiple competing views and hypotheses are presented regarding potential explanations.

Contextual Notes

Limitations include the lack of detailed information about the experimental setup, such as schematics and component datasheets, as well as the absence of specific measurements from the oscilloscope.

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.
 
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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.
 
Last edited:
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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