Question

我正在尝试使用以下代码。我希望我的LED慢慢消失，比如2秒/ 2000ms。编写的此代码与循环digitalWrite(2,HIGH)和digitalWrite(2,LOW)无法区分。我怀疑处理器如此快速地拉过255步，以至于衰落持续时间难以察觉。

void setup () {                        # set pin 2 as output
    pinMode = (2,OUTPUT);
}

void loop () {
    (for int fi=0;fi<255;fi++) {   # fade IN pin2 from 0-254
    analogWrite(2,fi)
    }
    (for int fo=0;fo<255;fo--) {   # fade OUT pin2 from 0-254
    analogWrite(2,fo)
    }
}

我想要一个或两个关于如何减缓淡化和淡化的建议。我最初的想法是在每个步骤中添加delay(8) ......但是这会出现更多的阶梯性功率增加而不是平滑的线性淡入淡出？这是一种最佳做法还是有更可接受的方式？

还有其他想法吗？

Answer 1

我会使用micros函数来更好地控制发出写入时的内容：

http://arduino.cc/en/Reference/Micros

这不是一个延迟，但只是返回自董事会上线以来经过的微秒数，用它可以做到这样的逻辑：

setup()
{
     t0 = micros()
}


loop()
{
    t1 = micros();
    dt = t1 - t0;
    if (dt > SOME_SMALL_TIME_DELTA)
    {
         increment_or_decrement_led_value_by_one();
         t0 = t1
    }
}

Answer 2

是的，你是正确的，不可能用微控制器创建真正的线性衰落。输出将始终具有一些最小步长或分辨率。对你而言，问题是“PWM是否具有足够的分辨率，以至于不会察觉到步骤？”

PWN可以255步输出0到100％。这与显示器上每个像素的8位分辨率相同。查看任何监视器校准页面，您可以说服自己，8位分辨率提供的内容基本上是平滑的。 Example monitor gradient

所以这是你的样本每4秒开启和关闭一个LED。这向您展示了如何在后台执行任务的几种方法。

4秒更改为关闭使用Blink without Delay Arduino docs中描述的方法。每次通过循环（），检查自上次更改后经过的时间是否超过指定的时间间隔 - 如果是，则更改状态并标记当前时间。

淡化效果略有不同。您将留下下一次更改的时间。每次旋转循环（），你检查是否是下一个动作的时间。如果是，则进行更改，并存储何时进行下一次更改。

/* unfortunately standard LED on pin 13 does not have PWM
You will need to connect an LED and resistor */
const int pin = 3;

/* this is your step time between changes in light 
output in milliseconds */
const unsigned int tstep = 8;

/* this is the time then next change can be made.
The change will happen at or after this value. */
unsigned int tnext = 0;

/* this is the current and target light level 
The output will slowly ramp until the current value
meets the target.  So to request that the change start,
the code just sets a new target. */
unsigned int target = 0;
unsigned int current = 0;

/* These are from Blink without Delay 
Shows another way to execute delays. */
unsigned long previousMillis = 0;
unsigned long interval = 4000;

void setup() {
   pinMode(pin,OUTPUT);
   tnext = millis() + tstep;
   analogWrite(pin, current);
}

/* something in the code calls this
to request a change in the LED state 
Pass what you want to be the new value
and the LED will slowly change to that value. */
void newTarget(int value) {
   tnext = millis() + tstep;
   target = value;
}

/* call this frequently to update the LED 
If the time of the next action has been reached,
execute the change and setup when the following
change will occur. */
void driveLed() {
   unsigned int tnow = millis();

   if(target != current) {
      if(tnow >= tnext) {
         if(target > current) {
            current += 1;
         }
         else {
            current -= 1;
         }
         analogWrite(pin, current);
         tnext += tstep;
      }
   }
}


/* Note that the main loop has no delays.
Execution will spin rapidly through this, most times
checking and finding nothing to to.
You would add your other functionality here, and this 
LED would continue to happen.  As long as you don't pack 
anything that takes on the order of 8 ms, you won't notice
a change in the LED fade behavior.
void loop() {
   unsigned int tnow = millis();

   // some other logic here would decide when to change the LED state
   // For this sample, just toggle every 4 seconds
   if((tnow - previousMillis) >= interval) {        
      if(0 == target) {
         newTarget(255);
      }
      else {
         newTarget(0);
      }
      previousMillis = tnow;
   }

   driveLed();
}

减慢Arduino FOR循环

2 个答案: