Very strange accidental proximity sensor - Explanation wanted

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Discussion Overview

The discussion revolves around an unusual behavior observed in an LED during an electronics project, specifically its activation in response to the user's proximity after being away for a period of time. Participants explore potential explanations for this phenomenon, including electrical charging and capacitive sensing, while sharing personal anecdotes related to similar experiences.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that the user may become electrically charged when leaving the room, creating an electric field that makes the LED conductive upon return.
  • Another explanation proposed is that the LED's behavior could be due to a capacitive sensor that requires time to charge between activations.
  • A third participant humorously suggests that the LED may have an emotional attachment to the user, lighting up more the longer the user is away.
  • One participant notes that similar phenomena can occur with CMOS components, recalling an experience where a device was actuated by hand proximity.
  • Another participant shares a personal experience with a microcontroller where an LED would illuminate slightly when approached, and interestingly, dimmed when the user grounded themselves.

Areas of Agreement / Disagreement

Participants present multiple competing explanations for the observed behavior of the LED, with no consensus reached on a single explanation. The discussion remains unresolved as participants explore different hypotheses and share related experiences.

Contextual Notes

Some explanations depend on assumptions about electrical charge and capacitive sensing, which are not fully explored or defined in the discussion. The lack of a schematic may limit the ability to provide more concrete advice.

Ngineer
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Hello everybody,

I was working on an electronics project, and one of the LEDs (actually I'm using only one) started acting really strange!

It will light up when I come close to it, ONLY if I have been out of the room for some time!

And that's not all, the period for which it will light up is proportional to how much I have been away (i.e. the longer I stay far from it the longer it will light when I return)


I was thinking of 2 possible explanations how this can happen,

Explanation 1. When I get out of the room I somehow get electrically charged, and this creates an E-field around the led when I return, making it conductive.
(But it will do this even if I go the other way (i.e. what matters is that I stay out of range, not where I go))

Explanation 2. The accidental sensor (be it capacitive or otherwise) is dependent on a capacitor that needs time to charge between "activations." But in this case it has a really wide range because I have to move 3~4 meters to get it to light again for a second or two!

Any input on this is appreciated, thanks!
 
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I think there's a third explanation. Could it be that the LED is in love with you and the longer you are away the more it misses you?
 
No possible way to give you any advice on this unless we see a schematic.
 
This gives me a grin. This is a classic when using CMOS components. When I was but a wee lad, my boss showed me a machine that he could actuate / de-actuate by waving his hand. It had an open gate and was picking up charge from his proximity (assumable he was charged).
 
I had a similar event recently - something I could not explain but seems simpler than your situation.

I was working with a microcontroller and had an isolated LED/resistor tied to ground. If I came close to the anode of the LED, it would very slightly eluminated. I made sure that I was not touching any charged electronics.

More interestingly, if I firmly placed my feet on the ground then the LED would become dimmer. It seems that I was somehow conducting charge whilst sitting there.
 

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