使用Arduino的2个光电传感器读取速度，读取后显示速度

我有两个NPN输出的光电传感器：查看数据表，它可能实际上很低（第14页NPN输出）：第14页

两个传感器相距152.4 mm。基本上，我想在第一个闸门被触发时启动计时器，在第二个闸门被触发时结束计时器，然后将设定的距离（152.4 mm）除以每个闸门之间的行程时间，以米秒为单位输出速度。传感器由24 VDC电源供电，NPN输出电压可高达集电极的3 V DC。我首先测试了传感器，当传感器前面有物体并且能够触发LED时，传感器会触发车载LED闪烁：

    const int sensorPin = 3; // photoelectric sensor
    const int ledPin = 13;
    boolean state1 = LOW; // state at startup

    void setup() {
      pinMode(sensorPin, INPUT_PULLUP); // sensor input with internal pullup 
      resistor enabled
      pinMode(ledPin, OUTPUT); // initialize digital pin 13 as an output.
    }

    void loop() {
      state1 = digitalRead(sensorPin);
      if (state1 == HIGH) {
        digitalWrite(ledPin, HIGH);
      }
      else {
        digitalWrite(ledPin, LOW);
      }
    }

因此，看起来电压在正确的范围内，可以读取为高或低

接下来我试着读速度。 代码如下：

const int PE_01 = 2;
const int PE_02 = 3;
unsigned long start, finish, speed;
float elapsed;
boolean state1 = LOW; //state at startup
boolean state2 = LOW; //state at startup

void setup() {
  // Initialize the serial communication at 9600 bits per second:
  Serial.begin(9600);
  pinMode(PE_01, INPUT_PULLUP); //sensor input with internal pullup 
  resistor enabled
  pinMode(PE_02, INPUT_PULLUP); //sensor input with internal pullup 
  resistor enabled
 }

void loop() {
  state1 = digitalRead(PE_01);
  state2 = digitalRead(PE_02);
   // time = millis ();
  if (state1 == HIGH){

    start = millis();
  }
if (state2 == HIGH) {
  finish = millis();
}
elapsed = finish - start;
speed = 76200/elapsed; // unit distance (micro meters) and time (milli 
seconds)
Serial.print("initial time (ms) = ");
Serial.println(start);
Serial.print("final time (ms) = ");
Serial.println(finish);
Serial.print("Speed of object (M/s) = ");
Serial.println(speed);
 delay(500);
}

然而，我在串行监视器中看到的是：

10:31:07.632 -> initial time (ms) = 15502
10:31:07.666 -> final time (ms) = 15502
10:31:07.666 -> Speed of object (M/s) = 4294967295
10:31:08.109 -> initial time (ms) = 16002
10:31:08.144 -> final time (ms) = 15502
10:31:08.178 -> Speed of object (M/s) = 0

---

当没有对象存在时，4294967295显示，当有对象存在时，它似乎输出0。我已经对等式进行了几次调整，但似乎没有得到任何有意义的结果。非常感谢您的帮助。谢谢大家!

代码的逻辑似乎不正确。 根据您的解释，如果您确定触发状态为高，我的代码将如下所示

void loop() {

  if (digitalRead(PE_01)== HIGH){// Check if first sensor trigged
      unsigned long start = millis();
      while(digitalRead(PE_02)== LOW);// Wait until second sensor trigged
      unsigned long finish = millis();
      float speed = 76200.0f/float(finish - start ); 
      Serial.print("initial time (ms) = ");
      Serial.println(start);
      Serial.print("final time (ms) = ");
      Serial.println(finish);
      Serial.print("Speed of object (M/s) = ");
      Serial.println(speed);
      delay(500);
}

编辑 如果您的传感器处于低电平，则反转所有逻辑

void循环（）{

---

当我回来的时候，我会试试这个，看看它是否运行，让你知道，谢谢M labNow，它看起来像是倒计时，串行监视器输出只是打印速度每次下降，不管门是否触发。当触发时，传感器的输出是什么？电压输出是什么？这是什么意思？我是指传感器检测时的逻辑输出是高还是低？

  if (digitalRead(PE_01)== LOW){// Check if first sensor trigged
      unsigned long start = millis();
      while(digitalRead(PE_02)== HIGH);// Wait until second sensor trigged
      unsigned long finish = millis();
      float speed = 76200.0f/float(finish - start ); 
      Serial.print("initial time (ms) = ");
      Serial.println(start);
      Serial.print("final time (ms) = ");
      Serial.println(finish);
      Serial.print("Speed of object (M/s) = ");
      Serial.println(speed);
      delay(500);
}