Re: [beagleboard] Re: I cannot output to GPIO pins.

[Chad Baker]

If you have an led with a forward current of 2ma and a forward voltage 
of 1.6v, connecting to the gpio pin directly, you would need a resistor 
of (3.3 - 1.6)/.002 = 850Ohms, a 1K resistor would probably work.
If you have an led with a forward current of 20ma you need to add a 
transistor to get the needed current boost because the gpio current 
output is limited to either 4ma or 6ma. Check the Device Summary for the 
AM335x from TI for the current limits of your gpio pin.
Chad

On 3/25/15 8:21 PM, cpp-...@hotmail.co.jp wrote:

    Thank you so much!!


I can do that.

But I had new problem.

The pin P8_3 that GPIO number is 38  can't output voltage...

I connected a LED through the resistance to P8_3 from GND.

But the LED don't light...

I wrong how to connect the LED?
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Chad Baker
Professor Emeritus
Electrical and Computer Engineering
Christian Brothers University
cmba...@cbu.edu

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