c++ - 使用带有 PIR 传感器的毫秒检测连续运动

Question

我正在尝试检测 PIR 传感器何时触发连续运动超过 8 秒。这是我所拥有的。当传感器处于低电平时，显示“无 Action ...”，然后短 Action 会触发第一个“< 8 秒”IF 语句。当传感器返回到低电平时 - 没有显示应有的运动，但是当第二次检测到运动时，代码似乎卡住并且没有任何反应。

unsigned long startMillis;
boolean timingFlag  = false;
const int buttonPin = 2;
int buttonState = 0;

void setup() {
   pinMode(buttonPin, INPUT);
   Serial.begin(19200);
   delay(500);
}

void loop() {
  buttonState = digitalRead(buttonPin);
  if (buttonState == HIGH && millis() - startMillis <= 8000UL)
  {
    Serial.println("Motion Detected but less than 8");
    delay(1000);
    //the PIR timed out with in the three seconds so cancel timing
    timingFlag = false;    //disable timing 
  }

  if (buttonState == LOW)
  {   
    Serial.println("No Motion...");   
    delay(1000);
    timingFlag = true;     //enable timing       
  }
  //when nine seconds have gone by with consistant detection do something
  if (timingFlag == false && millis() - startMillis >= 9000UL)
  {
    //There has now been nine seconds of constant PIR detection
    Serial.println("Motion Detected and greater than 9 sec");
    delay(1000);
    //Do Something   
  }
}

Answer 1

正如 Scheff 在评论中提到的那样，您当前的代码存在一个非常明显的问题:您实际上从未设置过 startMillis任何东西，所以它们可能(但不一定)总是 0。

这意味着语句 if (buttonState == HIGH && millis() - startMillis <= 8000UL)将始终为false 8000 毫秒后(直到 millis() 流过，大约 50 天* 后)，所以 timingFlag永远不会重置为 false在那之后。这最终会导致您的“卡住”情况。

我试图找到一个设置 startMillis 的好地方在你的代码中，但老实说我觉得它有点困惑，所以我允许自己重写你的逻辑，希望你不介意。 (请注意，我还将变量名称从按钮更改为检测器，因为它看起来更适合我):

(此版本在从高电平到低电平的转换时触发)

// define the threshold, after which an action shall be triggered
const int detectionThreshold = 8000;
const int detectorPin = 2;

unsigned long startTime = 0;
int lastDetectorState = LOW;

void setup() {
   pinMode(detectorPin, INPUT);
   Serial.begin(19200);
   delay(500);
}

void triggerDetectionAction(){
    // do whatever needs to be done after 8 seconds of motion in here
}

void loop() {

    int currentDetectorState = digitalRead(detectorPin);

    // if detector is low, no motion is detected
    if( currentDetectorState == LOW ){
        // when the detector is LOW, we want to check if the last state was HIGH
        // because then we just arrived at the transition from HIGH to LOW =>
        // "something was detected" to "there is no longer something detected"
        if( lastDetectorState == HIGH ){
            // then, we can get the total duration, the detection lasted
            unsigned long detectionDuration = millis() - startTime;
            // and print it for easier debugging
            Serial.print("Detection ended after ");
            Serial.print(detectionDuration);
            Serial.println(" milliseconds");

           // finally, we check if the durations was more than
           // or equal to our threshold
           if( detectionDuration >= detectionThreshold ){
               // and trigger stuff if necessary
               triggerDetectionAction();
           }
        }

        // if last detector state was LOW too, 
        // we don't want to do anything

    }else{

        // here we wan't to check for the transition of LOW to HIGH, 
        // so we check our last detector state
        if( lastDetectorState == LOW ){
            // if we caught the transition, 
            // set the start time to the current millis
            startTime = millis();

            // we could also set an indicator LED
            // or Serial.print something here
            Serial.println("Detection started");
        }

        // otherwise, we don't wan't to do anything

    }

    // finally, we save our current state into the last state, 
    // so we have it available in the next loop
    lastDetectorState = currentDetectorState;

    // do your other loop stuff here

}

请注意，我在编写时无法测试代码，因此可能存在(语法)错误

*更多关于毫秒和溢出的信息:https://www.arduino.cc/reference/en/language/functions/time/millis/

---

更新:该版本会在达到阈值时立即触发。它还包含一个示例，说明如何在达到阈值后每次循环触发一次操作。

// define the threshold, after which an action shall be triggered
const int detectionThreshold = 8000;
const int detectorPin = 2;

unsigned long startTime = 0;
int lastDetectorState = LOW;
bool actionTriggered = false;

void setup() {
   pinMode(detectorPin, INPUT);
   Serial.begin(19200);
   delay(500);
}

void triggerOnce(){
    // this will be called once, when the threshold is reached
}

void triggerEveryLoop(){
    // this will be called every loop, after the threshold was reached
    // for as long as the detector stays high
}

void loop() {

    int currentDetectorState = digitalRead(detectorPin);

    if( currentDetectorState == LOW ){

        if( lastDetectorState == HIGH ){
            // since we want to trigger immediately when the threshold is reached,
            // we actually don't need this transition any longer.
            // We can still keep it for debugging reasons thought.
            // If you don't need this, you can simply remove the entire block
            unsigned long detectionDuration = millis() - startTime;
            Serial.print("Detection ended after ");
            Serial.print(detectionDuration);
            Serial.println(" milliseconds");
        }

    }else{

        // Check for LOW => HIGH transition change
        if( lastDetectorState == LOW ){
            // if we caught the transition, 
            // set the start time to the current millis
            startTime = millis();

            // and reset the flag
            actionTriggered = false;

            // we could also set an indicator LED
            // or Serial.print something here
            Serial.println("Detection started");

        }else{

            // otherwise we want to check the duration
            unsigned long detectionDuration = millis() - startTime;

            // and trigger immediatley when the threshold is reached
            if( detectionDuration >= detectionThreshold ){

               // as long as it wasn't already triggered before
               if( !actionTriggered ){

                   Serial.println("Threshold reached, triggering");

                   // now we also need to set a flag, so we know we already triggerd this action once
                   actionTriggered = true;

                   triggerOnce();
               }

               // we can also do something every loop
               // this can be handy for e.g. blinking a light or playing a sound or something
               triggerEveryLoop();

           }

        }

    }

    // finally, we save our current state into the last state, 
    // so we have it available in the next loop
    lastDetectorState = currentDetectorState;

    // do your other loop stuff here

}