# 4. 数字-模拟转换器

DAC的用途和ADC正好相反，DAC是将数字信号转换成模拟信号输出。

还记得NyBoard开机的那一段音乐？那是使用PWM发出的，PWM采用高速开关调节占空比来输出电压。

相比PWM，DAC会直接输出电压而无需计算占空比。ESP32集成了1个2路8位DAC，数值为 0 - 255。电压范围是 0 - 3.3V。所以DAC的输出电压计算公式如下：

$$
DAC = （int）TargetV / 3.3V \* 255
$$

例程如下：

```
#define DAC1 25 

void setup() {  
}

void loop() {
  
  // 8bit DAC, 255 = 3.3V, 0 = 0.0V 
  for(int i = 0; i < 255; i++){
    dacWrite(DAC1, i);
    delay(10);
  }
}
```


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