From: Deniz P. <ap...@gm...> - 2006-06-04 19:29:27
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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 Best Regards, DEniz On 6/4/06, Dave Hylands <dhy...@gm...> 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 > clear > > 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: > http://members.misty.com/don/ledd.html > > 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 > http://www.DaveHylands.com/ > > > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users > |