LED guides for complete noobie! Working out voltages?

[gizmo1990]

First off apologies if this question or similar has already been asked but Ive searched and couldnt find anything?

I'd like to replace some LED's inside an internal card reader with some nice blue ones to match the rest of my set-up. Problem is I admit to knowing nothing about LED's and my electrical knowledge is very limited... However, I'm pretty nifty with a solder iron!

With this in mind does anyone know of any good guides explaining the principals involved in correctly replacing/rewiring LED's, such as correct voltages, using resistors etc??

I'd like to think it would be as easy as cutting off the old LED and soldering on a replacement but I know this isnt the case. I know LED's can require different currents etc but don't know how to work this out? How would I find out what voltage LED's my card reader uses?

Again Im sorry if this sounds really simple stuff but hey we've all got to start somewhere right...!?

Jim.

[subucni]

this might be obvious but it's worth saying,
one thing to remember is that LED's are diodes, so they'll only let current pass in one direction which could cause you problems, because it'll mean before you even get into currents and voltages you'll need to know what direction the current is flowing in the existing curcuit before you take off the old LED, so you know which way the new one will need to go.

with all that said though, i suppose if you're not worried about damaging the curcuit you could always just solder it on, try it, if it doesn't work unsolder (is that a word or is it de-solder,nevermind) it and solder back the right way

[emul8]

Multimeter sudenly srings to mind! check your volts and amps then go and buy the correct LED

[unrealrocks]

BitTech have an LED Calculator IIRC.

Normally you can get away with simply taking out the old LED and putting a new one in as long as your changing like for likeish (IE not upgrading it to a 12,000MCD )

[Steve]

Multimeters are the way forward. You can work out the voltage, and the polarity of the existing LED, then buy similar and put it in the right way.

Sorted!