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Topic: trouble getting leds to light on 3.3v arduino pro mini with Lipo supply (Read 1 time) previous topic - next topic

Katzmatt

so when the led it supposed to light up (digitalWrite(5,HIGH) it lights but very dimly
the resistors are proper and the voltage when it is connected pin led resistor ground is about 1.6 volts to 1.8 volts

but when the pin is disconnected from the led it gives me 3.3 volts as it should im very confused because the power supply is able to handle this and if i hook directly to VCC>led>resistor>gnd it lights up really bright as it should
i am not sure why the voltage drops so much because i know i am within limitations because my decimilia works fine when i do this

i was thinking of putting in a transistor but i really dont have enough space to put it in
any help would be much appreciated

Grumpy_Mike

Quote
the resistors are proper

Yes but what was the value? And what was the forward voltage drop of the LED?

Katzmatt

330 ohm and about that.. i dont know it and it s not on the datasheet
http://www.sparkfun.com/products/10442
thats what i have the datasheet only gives info on the button not the led in the button people say about 2 something volts is best and current is about 50ma but its strange how the voltage on the pin drops so much

Docedison

reduce the value of the series resistor. Assume 10 ma @ 2V and a red led with a (Typical) Vfwd of 1.8V. Therefore R = E/I  = 180 ohms based on 2 volts port voltage and a max of 20 ma... IMO

Doc
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Katzmatt

i have even tried removing the resistor and it still lights at the exact same brightness ok?
and when i supply it direcly with 3.3 volts with the resistor and led it lights up as it should

Osgeld

are you setting the pin to output? if not it will do exactly what you describe
http://arduino.cc/forum/index.php?action=unread;boards=2,3,4,5,67,6,7,8,9,10,11,66,12,13,15,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,86,87,89,1;ALL

Katzmatt


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