今天尝试使用PWM控制led和电机，按照教程写下如下程序：
int ledPin = 2; // 设定控制 LED 的数字 IO 脚
int val; //定义一个变量
void setup()
{
pinMode(ledPin, OUTPUT); // 设定数字 IO 口的模式， OUTPUT 为输出
}
void loop()
{
for(val=0;val<255;val++) //变量循环+1
{
analogWrite(ledPin, val); //PWM 输出
delay(50); //设定延时时间
}
for(val=255;val>0;val--) //变量循环-1
{
analogWrite(ledPin, val);
delay(50);
}
}
编译的时候提示error: 'analogWrite' was not declared in this scope
经多方查找以后发现esp32中并未实现analogWrite方法，详见analogWrite() not implemented #4
官方说法是这个函数正在搞，暂时可以用下面三个方法实现PWM：
16 channels LEDC which is PWM
8 channels SigmaDelta which uses SigmaDelta modulation
2 channels DAC which gives real analog output
下面是2个例子，分别使用SigmaDelta 和 LEDC
1、使用PWM：SigmaDelta实现呼吸灯效果，PIN2
int ledPin=2;
int val;
void setup() {
//设置 channel 0 频率为 312500 Hz
sigmaDeltaSetup(0, 312500);
//IO口 pin 18 附加到 channel 0
sigmaDeltaAttachPin(ledPin,0);
//channel 0 初始状态为关闭
sigmaDeltaWrite(0, 0);
}
void loop() {
for(val=0;val<255;val++)
{
sigmaDeltaWrite(0,val);
delay(50);
}
for(val=255;val>0;val--)
{
sigmaDeltaWrite(0,val);
delay(50);
}
}
2、使用LEDC控制led和电机
// use first channel of 16 channels (started from zero)
#define LEDC_CHANNEL_0 0
// use 13 bit precission for LEDC timer
#define LEDC_TIMER_13_BIT 13
// use 5000 Hz as a LEDC base frequency
#define LEDC_BASE_FREQ 20000
// fade LED PIN (replace with LED_BUILTIN constant for built-in LED)
#define LED_PIN 2
int brightness = 0; // how bright the LED is
int fadeAmount = 5; // how many points to fade the LED by
// Arduino like analogWrite
// value has to be between 0 and valueMax
void ledcAnalogWrite(uint8_t channel, uint32_t value, uint32_t valueMax = 255) {
// calculate duty, 8191 from 2 ^ 13 - 1
uint32_t duty = (8191 / valueMax) * min(value, valueMax);
// write duty to LEDC
ledcWrite(channel, duty);
}
void setup() {
// Setup timer and attach timer to a led pin
ledcSetup(LEDC_CHANNEL_0, LEDC_BASE_FREQ, LEDC_TIMER_13_BIT);
ledcAttachPin(LED_PIN, LEDC_CHANNEL_0);
}
void loop() {
// set the brightness on LEDC channel 0
ledcAnalogWrite(LEDC_CHANNEL_0, 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);
}
用上这段代码，nidec的无刷直流电机终于转动了
