Noob needs really basic LED/electronics help

[insound]

Hey

I've been a fan of this site for ages, but only have just joined up now because I need some help. I'm modding a keyboard; just the aesthetics, the case and everything, I had not planned to touch the electronics because... well I don't know what I'm doing.

But, I have messed up the design a little, and now need to do some basic tinkering - I need to remove 3 LED's, replace them with new ones (of a different colour) and also move them a few mm from where they are now.

The keyboard is very old, and the LED's look like this-

http://img690.imageshack.us/img690/5278/ledonkeyboard.jpg (http://imageshack.us/photo/my-images/690/ledonkeyboard.jpg/)

What kind of LED's should I replace them with? Is one LED as good as another? Surely the voltage and whatever affects which LED's I need to buy?

If I were to just de-solder them from the board and then solder in LED's like this (http://www.rshelectronics.co.uk/product.php?id_product=683), would that be all I need to do?

It just seems a little too easy! Don't I need to match them up somehow? Get the same type? or something?

Sorry if these are such basic questions, I'm just a real beginner with electronics and so want to make absolutely sure before I start ripping stuff up.

[NotNero]

without schematics and everything, nothing's gonna be 100% safe to do. That said, the basic function of a diode is to transmit electricity in one direction and not the other. Therefore, It's very important to make sure you get your + and - in the right direction. Unlike resistors, LED's have poles and will cause problems if soldered the wrong way. It would help if you knew the wattage of the LED's you're replacing, but as it's a keyboard, you can bet they're gonna be very low wattage. If you can match or approximate the wattages, are careful with polarity, and are sure handed enough to not bridge any traces with solder, you should be good to go.

I don't want to scare you, this is a relatively simple mod to undertake, and a great place to start getting comfortable with this kind of work, assuming the keyboard doesn't have a lot of personal, sentimental significance (just in case)! Just make sure you take it slow and practice the solder moves on something before trying it on the keyboard.

also, it looks like those LED's are just plugged into a socket so they may just pull out. That would make it really easy to replace, but not move, what you've got there!

[insound]

Thanks, that was exactly what I needed to know.

On some closer inspection of the board, I notice little tiny '+' signs on the left side of the LED's (you can see one behind the middle LED in the photo I posted, just about) so I guess that solves the polarity problem.

The only thing left then is the wattage. Do you have any advice on how I could find out the wattage? Is it safe to just take a guess? Any recommendations? The keyboard is a 20 year old mechanical board.

Also, no, I'm afraid they are not in sockets, it just looks like that. The white bit is just a ring of plastic from what I can make out, probably to stop the legs of the LEDs bending. It would be a lot easier if they did just slot out!

[NotNero]

well.. frankly, I don't want to recommend anything because i'm not sure.. I don't want to give bad advice!

..if it's old, I'm gonna guess ps/2 port connection. spec on that is 5v at a max of 250mA. That works out to a theoretical max of 1.25w. But depending on the circuitry, could be and is probably much,much lower..

If it were me, i'd bet at that low power, they're sold by mA or V. I'd get a ~4v or 20ma LED and see how it works. But you are not me and that is not my board. You should google keyboard mod forums and communities.. there seem to be a few from which you could cull rather specific advice and information.

Again, please use my reco as a starting place and not as a final answer. I have no way of knowing how your keyboards circuitry delivers power to those LEDs..

[insound]

Cool, thanks.

What would happen if I attached an LED with a voltage that was too high? or too low?

I mean, how badly could I mess things up? Is it just that the light simply wouldn't come on, or are we talking about real damage?

[NotNero]

I certainly can't rule anything out, when you talk about damage, you're talking about current or amperage. In this case, the max draw across the ps/2 plug .25 amps (250mA) So we're talking about a very small amount of current, nothing's gonna blow up, nothing's gonna melt. LED's come with a resistor value and a max current. The current is the voltage of the LED you're lookin for and resistor value is just a byproduct of the energy going into the emission of light. Most likely scenario is that it'll get noticeably hot if it's drawing too much or it'll be dim/not work if it's not getting enough.

IF you wanna see maths:
http://www.kpsec.freeuk.com/components/led.htm

[Bobnova]

You should be able to plop pretty much any LED in there and have it work, really.
It may be dim if the LED wants more voltage than the PCB is set up for, but it won't explode.
(Blue LEDs for instance want more voltage than red ones)

Worst case from just swapping LEDs is that the new LED dies.

[CompuTamer]

If you overvolt an LED, it'll either be the wrong color and die quickly, or it'll just have a shorter life span. (Green LEDs turn red at very high voltage)

If you undervolt it, it'll be dim.

Just find something that fits and try it. Maybe solder some temporary leads and try a few different LEDs. They're pretty cheap.