我在Arduino Nano上运行了一个PID循环，我计划通过USB连接到Raspberry Pi。我正在我的笔记本电脑上做一些测试，我试图确保它工作，但它不工作。代码发布在下面。你可以看到我在下面的循环中注解掉了target = sin函数。当target = rpm被注解掉时，而target = sin则不是。程序运行得很完美。然而，当我注解掉target = sin并取消注解target = rpm时，它不起作用。我已经在串行监视器窗口中向nano发送了值，并且我知道它已经接收到该值，因为我在监视器中看到“Transmission received”。当target = sin处于活动状态时，目标值也会在串行监视器中更新，但是当我发送一个值给串行监视器时，它的目标值显示为零。有人能解释一下我做错了什么吗？

#include <CytronMotorDriver.h> 

  // Configure the motor driver.
CytronMD motorR(PWM_DIR, 3, 4);  // PWM 1 = Pin D3, DIR 1 = Pin D4.

// Configure encoder pins
#define EncoderA 6 // yellow wire 
#define EncoderB 7 // green wire

volatile int posi = 0;      // position of motor
long previousT = 0;
float eprevious = 0;
float eintegral = 0;

int rpm;
int rpm_correction_factor = 1;
float wheel_circumference = 0.090;

// The setup routine runs once when you press reset.
void setup() {
  Serial.begin(9600);
  pinMode(EncoderA, INPUT);
  pinMode(EncoderB, INPUT);
  attachInterrupt(digitalPinToInterrupt(EncoderA), readEncoder, RISING); //whenever encoder phase A is HIGH, readEncoder function is called
  Serial.println("target position");
  }

// setSpeed can be any number for -255 to 255 (negative means reverse)
void loop() {
   //check if arduino has received some data. if data has arrived, use readStringUntil to get the next line. All bytes received until /n are converted to useable communication data
    if (Serial.available() > 0) {
        String received_speed = Serial.readStringUntil('\n');
        int rpm = round(rpm_correction_factor * (received_speed.toInt())/(wheel_circumference * 3.14 * 60));
        Serial.print("transmission received");
    }
  
  
  //int target = 250*sin(previousT/1e6); //test target position for PID control loop
  int target = rpm; //target position from serial port 

  //PID constants (these values may have to be adjusted)
  float kp = 1;
  float kd = 0;
  float ki = 0;

  //finding the time difference
  long currentT = micros();
  float deltaT = ((float)(currentT-previousT))/1.0e6;
  previousT = currentT;  

  int motor_position = 0;
  noInterrupts();
  motor_position = posi;
  interrupts();

  //error calculation
  int e = motor_position - target; //position and target may have to be switched depending on how the motor leads are wired

  //derivative
  float dedt = (e - eprevious)/(deltaT);

  //integral
  eintegral = eintegral + e*deltaT;

  //control signal
  float u = kp*e + kd*dedt + ki*eintegral;

  //set motor power and limit it to between -255 and +255
  //float power = fabs(u);
  float power = u;
  if(power>255){
    power = 255;
  }
  if(power<-255){
    power = -255;
  }

  motorR.setSpeed(power);
  //store previous error
  eprevious = e;

  //print target and position to serial plotter
  Serial.print(target);
  Serial.print(",");
  Serial.println(motor_position);
  //Serial.println();

 
}

void readEncoder(){
  // called when EncoderA is high; If the motor is rotating counterclockwise, EncoderB should already be high, so we would add one to the position 
  int b = digitalRead(EncoderB);
  if(b>0) {
    posi ++;
    }
  else{
    posi --;
    }
  }