Led

What is a LED?

1. A LED is a semiconductor device that emits light when an electric current flows through it.
2. Unlike traditional incandescent bulbs, LEDs don’t have a filament. Instead, they rely on the movement of electrons within the semiconductor material.

LED Structure:

A LED consists of several layers:

1. N-Type Semiconductor Layer: This layer has an excess of electrons.
2. P-Type Semiconductor Layer: This layer has an excess of “holes” (electron vacancies).
3. Active Layer (Quantum Well): Located between the N-type and P-type layers, this thin layer is where light emission occurs.
4. Metal Contacts: These allow current flow into and out of the LED.

How Does It Emit Light?

1. When a voltage is applied across the LED (usually around 1.5 to 3.3 volts, depending on the LED type):
2. Electrons from the N-type layer move into the active layer.
3. Holes from the P-type layer move into the active layer.
4. Electrons recombine with holes in the active layer.
5. During recombination, energy is released in the form of photons (light).
6. The color of the emitted light depends on the semiconductor material used (e.g., red, green, blue, etc.).

Polarity and Pins:

LEDs have two pins:

1. Cathode (-): Connect this pin to the ground (GND) or negative terminal.
2. Anode (+): Connect this pin to the positive voltage (VCC).

Reverse polarity (swapping the pins) won’t damage the LED but will prevent it from lighting up.

Forward Voltage and Current:

1. Each LED has a specific forward voltage (Vf) requirement (e.g., 2.0V for a red LED, 3.3V for a blue LED).
2. To prevent burning out the LED, use a current-limiting resistor (e.g., 220 ohms) in series with it.

Controlling Brightness:

1. To control brightness, use Pulse Width Modulation (PWM):
2. Rapidly turning the LED on and off at varying duty cycles.
3. Higher duty cycle = brighter light.

int led = 13; // the pin the LED is connected to
void setup() {
  pinMode(led, OUTPUT); // Declare the LED as an output
}

void loop() {
  digitalWrite(led, HIGH); // Turn the LED on
}