On Mon, 02 Feb 2009 14:51:36 GMT, John
wrote:

On Mon, 02 Feb 2009 14:40:24 +0000, John wrote:

I would like to change the led's in a old pc I recovered amber=power
green=hd from there factory color to different colors like blue and
super red led's.
I use to play electronic hobbies years ago so I’m concerned that if I
just solder the defferent color led’s to the leads I might fry
something.
Any help welcome

Sorry amber is HD and green is power.

---
Measure the supply voltage and get the voltage and current specs for the
new LEDs and then figure out what the values need to be for the new
series resistors, like this:


Vcc - Vled
R = ------------
Iled

Where R is the resistance of the resistor, in ohms,
Vcc is the supply voltage, in volts,
Vled is the LED forward voltage, (from the data sheet) and
Iled is the LED forward current. (from the data sheet.

Then determine how much power the resistors will be dissipating, like
this:


P = (Vcc - Vled) * Iled


where P is the power dissipated, in watts.

A convenient rule-of-thumb to follow is to use a resistor which is rated
to dissipate 2P.

Once you've done all that and you have the parts on hand, carefully
unsolder the old LEDs and resistors and solder in the new ones making
sure you don't get the LED polarities backwards.


JF