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Topic: Arduino Pro Mini - Resistor(R11) before PWR LED - why 10K?? (Read 2040 times) previous topic - next topic

bob4432

as title states, why is the resistor(R11) before the pwr led on the arduino/sparkfun pro mini 10K??



just seems so high even if somebody put in 16V which the schematic claims is possible.

thanks in advance,
bob



CrossRoads

Well, ideally the 16V is only applied to RAW, not the VCC pin, which would smoke the atmega.
The 10K just limits current draw by the LED, to ~(5V-2V)/10K = 0.3mA.
That way you're not sucking lots of battery life when using it in a portable device.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

bob4432

so, if you are not worried about batt life, one could use a 330? instead of using the more expensive low power leds if you were to build your own (plus i have lots of 330? R and 12mcd .20mA leds on hand :))?

CrossRoads

Yes.
20mA to get 12mcd - sounds barely viewable after using 4000mcd LEDs!
I don't even bother with power LED when I build my free standing arduino-based designs.
LEDs elsewhere make it obvious that power has been applied.

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

bob4432

will give it a try on my next one i build.  4000mcd, i would be blind, haha.  still using the leds to verify pwr is getting to certain places and i haven't made a mistake.  i hear you though, 20mA for 12mcd is not a good tradeoff, but i am running these on multirotors so i have 2.2-3+A batts so i am not too concerned about the efficiency, but in other areas i am starting to see how the leds add up, especially if you want to run stuff from a atmega pin where you are really limited

was a fun way to use/see if i could do 0402 only to realize the sparkfun info stated 0402 but used 0603  :smiley-eek:


these sure are fun to build, now am starting to make organic designs :)

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