Controlling a led, pull up resistor value

Questions and discussion about The WiPy 1.0 board and CC3200 boards.
Target audience: Users with a WiPy 1.0 or CC3200 board.
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danicampora
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Re: Controlling a led, pull up resistor value

Post by danicampora » Mon Nov 09, 2015 12:48 pm

While it may work, as a general rule NEVER drive a LED directly from a microcontroller port.
I was never suggesting that a series resistor was not needed. Normally I use something between 100 Ohm and 1K.

blmorris
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Re: Controlling a led, pull up resistor value

Post by blmorris » Mon Nov 09, 2015 3:22 pm

@bmarkus @danicampora:
bmarkus wrote:While it may work, as a general rule NEVER drive a LED directly from a microcontroller port.
My first thought on reading this was "wait a minute, why not? I've put something like 10K boards of various designs into production doing exactly that!"

Then I read the part about using a series resistor. Yes, always use a series resistor :lol:

-Bryan

AJWIFI
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Joined: Sun May 29, 2016 5:30 am

Re: Controlling a led, pull up resistor value

Post by AJWIFI » Sat Jul 23, 2016 2:39 pm

If using a Blue LED I have measured Vf at 2.7Volts (quite a bit higher than the Red/Orange/Yellow) and I believe white are similar to blue.

For Blue LED
(3.3-2.7)/0.005 = 120ohms min R required to draw max GPIO current

That said using a 330ohm with Blue LED which in this case would draw 1.8mA to me is bright enough

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