What resistor value should I use for LEDS

Design Concepts
1

Am I doing this right?:

I bought several LEDS at radioshack and I am using a 220 ohms resistor, for testing,

am doing backlit bottons (about 20 T1 Leds), could I use the same resistor value for each, also could I use the power out of the core??? for it.

2

try different values see what is acceptable.  Run it through a meter and see how much current you a drawing and its low with acceptable light level, you should be OK to run off of the core.  I got acceptable results with my clear blue LED’s using a 1k (which reduced the current draw from 120 mA per LED down to about 2.6 mA)

3

it’s in German, but you should be fine with that calculator:

http://www.elektronik-kompendium.de/sites/praxis/led-vorwiderstand.htm

If you have normal LEDs, each LED is using ~20 mA …there are also low current LEDs that just need about 2mA per LED;

Just add the mA and you’ll know how much current is needed. I’m not so sure about but (depending on the power supply you use) I’d say everything below 400 mA should be fine… if your 5V regulator gets too hot, you’ll know that it’s too much.

Regards,

Michael

4

thank you guys , i dont have a multimeter right now, could you tell me what values should I look for if am planing to put 31 LEDS all to be on at the same time I was thinking of getting voltage directly out of the wall adapter before it gets to the core, ?

any suggestions as far as led -resistor conbinations for 31 leds?