[使用Arduino的2个光电传感器读取速度，读取后显示速度

Question

1. 我有2个带NPN输出的光电传感器。 2个传感器相距152.4毫米。基本上，我想在第一个闸门触发时启动一个计时器，在第二个闸门触发时完成一个计时器，然后将设置距离（152.4毫米）除以在每个闸门之间移动的时间，并以米为单位输出速度。传感器由24 VDC电源供电，收集器的NPN输出电压可高达3V DC。我首先对传感器进行了测试，以便当传感器前面有物体并能够触发LED时，触发板载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HIGH或LOW。

所以接下来，我尝试读取速度。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);
}

但是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

4294967295在没有对象存在并且似乎有输出0的情况下显示。我对等式进行了几次调整，但似乎没有任何意义。任何帮助是极大的赞赏。谢谢！

Answer 1

代码逻辑似乎不正确。根据您的解释，如果您确定触发状态为HIGH，则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);
}