# 板载 PWM：呼吸灯

## 硬件连线

| 模块角标            | 龙芯派接口     | Python 引脚常量名 |
| --------------- | --------- | ------------ |
| VCC/IN (LED 正极) | P45: PWM0 | PWM0         |
| GND (LED 负极)    | P9: GND   |              |

## 代码

```python
import time
import board
import pulseio

led = pulseio.PWMOut(board.PWM0, frequency=5000, duty_cycle=0)

while True:
    for i in range(100):
        # PWM LED up and down
        if i < 50:
            led.duty_cycle = int(i * 2 * 65535 / 100)  # Up
            print("up    ", end="\r")
        else:
            led.duty_cycle = 65535 - int((i - 50) * 2 * 65535 / 100)  # Down
            print("down  ", end="\r")
        time.sleep(0.01)
```

程序运行后，LED 灯将会循环逐渐变亮后变暗。
