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I have bought a webcam from which I would like to remove an LED (burning it is also fine for me).

By doing so, I could obviously change the way the circuit works, so my questions are:

  1. Should I remove the LED (or its resistor) or burn it?
  2. Is a burnt LED short circuit or open?
  3. How can you be sure of what to do? Is there a convention for connecting LEDs?

By the way, the guy here just snapped the LED right off, but I couldn't understand how did he figure out that that won't damage the camera.

Also, there's this project, which shows the insides of another camera (which looks very much the same as mine)

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Why don't you just cover the LED with something? It would be the least risky thing to do. Tape a piece of aluminum foil over it and you're done. –  Adam Davis May 21 at 17:50
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@AdamDavis As I understand it, that is why black fingernail polish was invented. –  Wayfaring Stranger May 21 at 17:58
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Another idea would be to replace the LED with a non light emitting diode (i.e. regular diode) that has the same electrical properties (forward current voltage, resistance, etc) –  Wavy Crab May 21 at 18:43
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How many Electrical Engineers does it take to disable an LED? –  Robert Harvey May 21 at 20:24
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I don't see any responses here taking note of the fact that the LED on a webcam is intended to indicate that the camera is currently on, and may actually be designed to fail hard. As in, no LED, no camera. This helps prevent people from watching you sleep if the laptop is left open, for example. –  Jason_L_Bens May 22 at 1:30
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4 Answers 4

up vote 14 down vote accepted

Actually, I'd say that both of the other answers are half-wrong. The true answer is:

it depends.

Basically, there are 3 possible options (although they aren't the only ones possible):

1a) (most common) a LED receives a current through a current-limiting resistor, the current path ends after the LED (ground etc);

In this case you can safely remove the LED, making it open-circuit. You can keep the resistor, the current won't flow through it anyway.

1b) a LED receives a limited current through a constant or current-limited current supply, the current path ends after the LED.

In this case, you won't find a current-limiting resistor - but you can still remove the LED without any side effects other than small overall current consumption reduction.

2) a LED receives a unlimited current, but with a limited voltage. You may find this solution in some low-end electronics OR in cases where the supply voltage is about Vd of the diode.

In this case, since the entire voltage drop happens on the diode, it's rather impossible that the current powers anything else, so you can usually safely unplug/unsolder it.

3) a LED receives a current and the current path doesn't end after the LED. It may be used as a rectifier or voltage dropper.

In this case, removing a LED with disable and/or damage the whole circuit dependent on the current. It is rare, but not entirely impossible to find. The current will probably not be limited by resistor in this case, but rather by some current driving IC, although you may find a limiting resistor in this case (note that since it actually reduces the maximum current of the whole path, it is even rarer IMO). You may consider replacing it with a series of non-LE diodes, usually 3 or 4 would be okay, depending on the exact colour of LED etc.

Also, bear in mind that the visual signal from the LED may be used by an optic receiver somewhere (computer mouse LEDs come to mind here), so you may (although unlikely) end with an appliance not sending required feedback signal, thus not working properly or at all.

Now, how to distinguish those cases? The simplest way is to unplug/unsolder the diode, check the results. In 99% of the cases everything will work as usual.

NB, Doing a short circuit would damage solution 2), increase current consumption slightly (due to omission of diode's internal resistance) in cases 1a/b) and 3) and possibly stress/damage (although unlikely) some components in cases 1b) & 3). Doing an open circuit would disable all parts in series with the diode in case 3).

btw, burnt LEDs behaviour depends on the actual damage done to LED - although they usually simply increase their internal resistance heavily, so they approach open circuit after some time (like a fuse).

tl;dr in 99% of the cases simply remove the LED and don't worry about anything else. If the circuit malfunctions and the removal was done properly, either reattach the diode and cover it mechanically/visually OR replace it with a single non-LE diode (if rectification was used in original circuit) OR use a series of non-LE diodes with Vd ~equal to Vd of your diode. YMMV.

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This should be the accepted answer as it addresses all the possible circuit configurations, details how to test, and why chopping the LED out is a bad idea. –  Jason_L_Bens May 22 at 7:24
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I've seen some schematics where the LED is on a path used to power a circuit (or part of). It means if you remove the LED, the current won't flow, and the circuit won't work anymore. Look at this one:

enter image description here

If you remove the LED, the circuit that is connected to CNTLED won't be powered by IC22C anymore. So, it depends on how it is implemented.

If you don't know the schematics, I would advise you to replace the LED by a short circuit instead of an open circuit.

Why? Because when the LED is ON, it has a small resistance (much lower than the current limiting resistor in series with it). And when the LED is OFF, the voltage across the LED is too low (under the its threshold voltage). So a short circuit wouldn't hurt in this case.

I don't know if a burnt LED is likely to be like an open circuit or a short circuit.

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2  
ain't CNTLED is just a... control LED? I highly doubt if anyone would like to power anything other than another LED through a LED... –  vaxquis May 21 at 17:09
    
You're right, in this case it´s a LED, but in the invisible range (UV) –  RawBean May 21 at 20:47
    
Would it be a good idea to replace the LED with a diode in the same polarity? A jumper would be simpler, but wouldn't block reverse current the way the LED did. I'm guessing in most applications it wouldn't matter because LEDs are rarely used for their diode properties. –  mouseas May 21 at 22:07
    
@mouseas see my answer for details. In general, yes. –  vaxquis May 21 at 23:25
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I've seen some circuits where the LED is an integral part of the circuit. I had a Fender guitar amp that used LEDs for their clipping the audio. LEDs can also be used in single-bipolar current source circuits.

The lowest-risk way to disable an LED is to paint it with some black paint.

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For the best opacity, use a synthetic paint. Vinyl if the camera is positioned where it may receive sunlight, or latex if indoors. Use a couple of coats and you should be good. If you need a fool-proof long term solution, simply coat the paint with epoxy to make sure it can't separate or bubble over time. –  David Wilkins May 21 at 19:14
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A LED is connected in series with a current limiting resistor. The LED-resistor circuit is connected across the power supply in parallel with other circuits.

So removing the LED or the current limiter resistor shouldn't affect other circuit.

Better remove the LED, instead of burning it. It may get closed circuit and increase the current drawn and heat of resistors.

Only if the webcam isn't working anymore, make a closed circuit (place a jumper across LED terminals) - see vaxquis' answer. But it is unlikely in this situation, where you have a LED used for making light.

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Are there scenarios in which you would connect a led in series with other components (besides other leds, limiting resistors, etc) –  Nitay May 21 at 10:09
    
@Nitay yes if it can be controlled via software, then the LED is connected through a transistor driver. But there is no problem if you remove the LED in this case. –  Cornelius May 21 at 10:12
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Ok, anyway I removed the LED. All is well –  Nitay May 22 at 12:37
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