What value resistor to use with blue LED?

[kloan]

I was using a 10k ohm resistor on the (+) signal to a blue LED in my cmoy. Is this ok, or should I be using another value resistor so that it doesn't draw too much power?

 

[Daroid]

Well, do you know the voltage drop over the LED and suggested current rating ? Blue LEDs tend to have a higher voltage rop than e.g. red, yellow, green.
3.5V is not attypical, and give it 20 mA so it will not be too bright again...

R=U/I

If you have a 9V source then that's:

R=(9-3.5V)/0.020 = 275 Ohm. It will be safe and plenty bright in most cases

Give it around 200 Ohm if you're using an alkaline or 250 Ohm if you're using a 8.4V NiMH IMO

EDIT: 10k will work yes, but you might find that it is not bright enough. It will be fine in cases where you don't want to draw much power - but depending on it's characteristics on luminousity it might not be bright enough... a datasheet would help

 

[Nisbeth]

Well, erm what is your PSU/battery voltage? The voltage drop across a blue LED is typically 3V and you would normally like to have something like 3 mA (0.003A) through the LED. If you're using a 9V battery, the resistor should be (9V-3V)/0.003A = 2000 ohms. Depending on desired battery life, desired LED brightness and avaialble supply voltage, you'll have to modify these numbers for yourself.

/U.

 

[kloan]

I'm using a 9V battery.. I know the LED is 3V min. but not sure about the other stuff.. using a 10K was plenty bright so I guess I'll stick with it..

thanks

 

[AMZ-FX]

Use my online calculator for LED resistors:

http://www.muzique.com/schem/led.htm

regards, Jack

 

[kloan]

cool, thanks