Changing LED's for beginner

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BuudWeizErr

Gawd
Joined
Jan 14, 2002
Messages
856
Hi guys,

I have a device that flashes a red LED, I'd like to replace the LED's with LED's of a different color.

I'm more of a hardware guy; I know my way around an iron and desoldering wire, what I don't know is how to tell what the specifications are on my existing LED's are, in order to buy new ones.

Here is the PCB with LED's I speak of; there is no writing on the PCB at all that might help.

IMG00058.jpg

IMG00059.jpg


Can someone point me in the right direction? TIA!

edit: +10 points if you can figure out what its from.
 
They're either 3mm or 5mm in size. Looks like 5mm in the blurry photo.

Nearly all 5mm LEDS want a forward current of 30 to 50mA, so you should be set there. Some different colors have a different forward voltage drop, which shouldn't be a problem if they're being driven properly with a current source. It's possible another color may be dimmer than the red ones.

http://superbrightleds.com/leds.htm
Or there's a bunch of distributors on eBay as well.

Polarity does matter, as with most components the longer lead is the positive one. If the polarity is not marked on the silkscreen of your circuit board, you can look closely at them to tell. Notice the flat edge on the negative side, and the shape of the junction inside the LED itself.
image_preview
 
It looks to me like the only things on that circuit board are the two LEDs and a pair of resistors. Since the original LEDs are red, you can safely drop in any other LED in their place.

(The reason it's safe is a bit more on the technical side--red LEDs have a smaller voltage drop, and since they are in series with the resistors, the resistors therefore have a higher voltage drop. If you put in a blue or white or green LED, the new LED will have a higher voltage drop, which means a lower voltage drop for the resistors. Lower voltage drop means you'll get less current, and less current is always safe when you're dealing with LEDs. If you want to get the same amount of current through the new LEDs, you'll need to swap out the resistors, which becomes a bit more involved, as the one on the PCB are surface-mount and rather small)
 
great, thanks for the info guys. i'll bump this thread if i have questions later, but I think this is a good jumping off point.
 
Why don't they just make them like this, so that even after clipping the leeds there is no doubt?

 
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