Why is the Small LED on my Screwdriver Lighting Up?

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Discussion Overview

The discussion revolves around the functioning of a small LED in a screwdriver, particularly when it lights up upon contact with the user's skin. Participants explore the mechanisms behind this phenomenon, including the possibility of a battery, the role of human electrical signals, and the nature of voltage detection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant hypothesizes that the LED lighting up indicates a potential difference between fingers, suggesting the presence of a battery in the screwdriver.
  • Another participant confirms that the screwdriver is a Voltage Detector, implying it has an internal battery.
  • A different participant considers the possibility that the LED requires very little voltage to illuminate and questions the longevity of the battery in an old screwdriver.
  • One participant shares experiences with electrical signals from the human body, noting phenomena observed with an oscilloscope and an iPod docking station, suggesting that the body emits electrical signals that might affect the LED.
  • Another participant mentions that the human heart generates a small electrical field, which is relevant to heart rate monitors and defibrillation.

Areas of Agreement / Disagreement

Participants express varying hypotheses about the LED's operation, with some agreeing on the presence of a battery while others question the mechanics of voltage detection and the role of the human body's electrical signals. No consensus is reached regarding the exact cause of the LED lighting up.

Contextual Notes

Participants acknowledge uncertainties regarding the voltage drop between fingers and the specific mechanisms by which the screwdriver detects voltage. The discussion includes assumptions about the electrical properties of the human body and the functioning of the screwdriver.

Mephisto
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I have a small screwdriver which has a small LED in it. When you stick it into something like an outlet, and hold your finger on the other end, the LED lights up. Today though I held both ends of the screwdriver and the LED lighted up. This confuses me tremendously... Doesn't that indicate there is a potential difference between the two fingers? Otherwise what makes electricity flow and light up the LED? Does anyone know these screwdrivers? My best hypothesis is that it must have a battery in it or something, and some type of a small ammeter or something?
 
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It actually does have a battery inside. Lol, you thought you could obtain energy from your fingers? Thats great. Such a device is chiefly called a Voltage Detector or Voltage detection screwdriver.
C.f.: Patent 6100679 - Abstract & Schematics

(google is sortof starting to scare me with its versatility)
 
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no i thought that the LED just requires VERY little voltage to start shining... And it's pretty dim too so i thought it was a possibility that I was charged or something... but not uniformly? sounded weird. Anyway the thing that confused me the most was that the screwdriver is REALLY old, and the battery would have to last a really long time as well.
ok cool good to know... and i was right :p
thanks for the link

there still is the issue however of why it lights up on contact with my skin...
"A tool for indicating the presence of potentially dangerous voltages to the user includes circuitry for detecting the presence of an AC voltage..."
i'm still not exactly sure how it works. it's probably easy to detect high voltages, but the voltage drop between my two fingers should be pretty much 0.
 
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Mephisto said:
i'm still not exactly sure how it works. it's probably easy to detect high voltages, but the voltage drop between my two fingers should be pretty much 0.

When I hold the tip of an oscilloscope probe between thumb and forefinger, I see a periodic trace on the scope.

Similarly, I have an iPod docking station with speakers. It includes a cable (mini plug to mini plug) for connecting auxiliary devices other than the iPod to its speakers. When I connect myself to it (i.e. I turn on the unit, plug one end of the cable into the mini jack, and hold the contact of other end between thumb and forefinger), I hear a buzzing noise over the speakers.

The human body emits some type of electrical signal. I think it's related to what keeps one's heart beating, but I don't know too much about this topic.

I also am not sure if that is what is lighting your LED.

Can anyone explain the cause of these phenomena in more detail?
 
The human heart gives off a small electrical field. Thats how most heart rate moniters work, by picking up this field. Also has to do with why they shock you to get your heart started agian.
 

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