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BE15000090

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The Light Emitting Diode, also known by the acronym LED is used for light emission and instruments in locations where it is more convenient to use in place of a lamp. Especially used in microelectronics products as warnings flag, can also be found in larger, as in some models of traffic lights. It is also used in LED panels, LED curtains, LED trails and street lamps, allowing a significant reduction in electricity consumption.

 

 

As the LED, the LED can not directly receive voltage between its terminals, since the current must be limited so that the junction is not damaged. Thus, the use of a limiting resistor in series with the LED is common in systems that use it. To calculate the value of the resistor is used the following formula: R = (Vfonte-VLED) / ILED where Vfonte is available tension, VLED is the correct tension for LED in question and ILED is the current that he can support with safety.

Typically, LEDs large (approximately 5 mm in diameter when round) working with currents of the order of 12 to 30 mA and the small (approximately 3 mm in diameter) operate with half of this value.

Like this:

We adopt I1 and I2 = 15 mA = 8 mA, Vsource = 12 V, VLED = 2 V:

R1 = (12 - 2) / 10 = 0.015 / 0.015 = 680 *

R2 = (12 - 2) / 10 = 0.008 / 0.008 = 1K2 *

We approach the results for the closer commercial values.

LEDs do not support reverse voltage (VR) of significant value, being able to damage them with only 5V voltage accordingly. Therefore, when powered by AC voltage, the LED is usually accompanied by a rectifier diode in antiparallel (reversed polarity in relation to the LED), in order to drive the half cycles in which it - the LED - is the sectional limiting this reverse voltage around 0.7V (maximum forward voltage of diode), a sufficiently low value so that its junction is not damaged. Also can adopt a series connection between the diode protection and LED.

 

Arduino Conecction:

 

Code:

/*
Fade

This example shows how to fade an LED on pin 9
using the analogWrite() function.

The analogWrite() function uses PWM, so if
you want to change the pin you're using, be
sure to use another PWM capable pin. On most
Arduino, the PWM pins are identified with
a "~" sign, like ~3, ~5, ~6, ~9, ~10 and ~11.

This example code is in the public domain.
*/

int led = 9; // the PWM pin the LED is attached to
int brightness = 0; // how bright the LED is
int fadeAmount = 5; // how many points to fade the LED by

// the setup routine runs once when you press reset:
void setup() {
// declare pin 9 to be an output:
pinMode(led, OUTPUT);
}

// the loop routine runs over and over again forever:
void loop() {
// set the brightness of pin 9:
analogWrite(led, brightness);

// change the brightness for next time through the loop:
brightness = brightness + fadeAmount;

// reverse the direction of the fading at the ends of the fade:
if (brightness == 0 || brightness == 255) {
fadeAmount = -fadeAmount ;
}
// wait for 30 milliseconds to see the dimming effect
delay(30);
}

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