LEDs in Mouse & Resistors

[Bruce]

Hi,

I want to add some LEDs to my mouse. The output of the mouse is 5v. I
have heard that there is really no such thing as a 5v LED, even if the
LED is labeled as 5v. I'm thinking of using 3v (20ma) LEDs with
resistors. What size resistors should I use? I have already tried a 3v
(20ma) LED without a resistor, but the LED quickly overheats and changes
color.

I have another question. If the output of the mouse is 5v, does a 3v LED
use 3 of the 5v, therefor leaving only 2v of output left? In other
words, let's just pretend there are such things as 5v LEDs...Can I attach
three 5v LEDs to a 5v power source? Or does one 5v LED use all the power
by itself? If it does use all the power, is there a way to get around
this problem?

Thanks,

Jeff

 

[John Doe]

Hi,
Lo,

I want to add some LEDs to my mouse. The output of the mouse is
5v. I have heard that there is really no such thing as a 5v LED,
even if the LED is labeled as 5v. I'm thinking of using 3v (20ma)
LEDs with resistors. What size resistors should I use?

You must use a series resistor, looking for some "5 V LED" is a
waste of time. Use an ordinary LED.

The LED foreword voltage drop helps determine resistor value, don't
waste your time trying to match it with the supply voltage. That's
not going to happen.

To determine the correct resistor value goes something like this.
Given a 5 V supply and an LED with a 1.5 V (or whatever it is
specified) forward voltage drop, first subtract the voltage drop
from the supply voltage. In this example, that leaves you with 3.5
V. Then if you want 15 milliamps flowing through your LED, divide
that into 3.5 to get approximately 233 ohms, and use the next higher
available resistor value.

I have already tried a 3v (20ma) LED without a resistor, but the
LED quickly overheats and changes color.

That should have quickly destroyed the LED.

If the output of the mouse is 5v, does a 3v LED

Do not try to match LED voltage with supply voltage. If I were you,
I would ask a few basic electronics questions in the basic
electronics group.

Good luck.