Thanks Dave But,
I connect a 4.8V led to CN6 ST-UART GND and transmit data, but when i set
GPIO i see no light :( . Ok i expect only a small light not a bright one.
What did i do wrong? I used following commands:
echo "GPIO out set" > /proc/gpio/GPIO47
echo "GPIO out clear" > /proc/gpio/GPIO47
On 6/4/06, Dave Hylands <dhylands@...> wrote:
> hi Deniz,
> > I will try to light a LED with Breakout-gs, but before i try i
> think it
> > is better to ask the list. Are there any difference using any CN? I will
> > connect the LED directly to GPIO and GND I guess, and echo set and
> > the GPIO. I affraid to burn gumstix becouse of possible high current.
> Can i
> > try this scenario directly? What are the things that i must care about?
> You'll also need a current limiting resistor, otherwise the LED will
> live a very short life.
> Here's a page that walks you through figuring out the correct value:
> A typical run of the mill red led will have a voltage drop around
> 1.7v. The GPIO pins on the PXA255 are only rated to 10 mA, so we can't
> exceed that. 15 mA would be a bit better, but you should use a
> transistor or buffer driver if you're going to exceed the specs.
> So now, we use ohms law. V = I x R, where V = 3.3 - 1.7, I = 0.010,
> and we're trying to find R. So R = V/I = 1.6 / 0.010 = 160 ohms.
> So you need a resistor with at least 160 ohms. Higher is fine, it will
> just cause the LED to be a bit dimmer. 180, 220, 270, 330, 390, and
> 470 are common values above 160.
> As far as which CN to use, no it doesn't really make any difference. I
> would avoid the FFUART.
> Dave Hylands
> Vancouver, BC, Canada
> gumstix-users mailing list