## PWM
***Pulse Width Modulation*** / Modulación por ancho de pulso

[Arduino.cc](https://docs.arduino.cc/learn/microcontrollers/analog-output)

| Placa | Pines PWM | Frecuencia PWM |
| -     | -         | -              |
| Uno, Nano, Mini | 3, 5, 6, 10, 11 | 490Hz (pines 5 y 6:980 Hz) |
| Mega | 2 -13, 44-46 | 490Hz (pines 4 y 13:980 Hz) |
| Micro | 3, 5, 6, 9, 10, 11, 13 | 490Hz (pines 3 y 11:980 Hz) |

[Arduino.cc](https://www.arduino.cc/reference/en/language/functions/analog-io/analogwrite/)

#### PWM pin 9
```c
#define LED 9

void setup() {
    pinMode(LED, OUTPUT);
}

void loop() {
    for (byte i=20; i<255; i++) {
        analogWrite(LED, i);
        delay(5);
    }
    for (byte i=255; i>20; i--) {
        analogWrite(LED, i);
        delay(5);
    }
}
```