兩種Arduino環境下開環控制自平衡小車程序（只有直立環）

1.硬件電路

從左往右，依次是MPU6050陀螺儀模塊，Promin 開發板，DRV8833電機驅動，兩塊升壓板，將18650電池電壓升高至5V。減小干擾，驅動電路與控制電路分離，所以用了兩塊升壓板。依賴的庫在代碼頭部說明裏，代碼是在前人基礎上改的，文章最後有參考鏈接。

2.電機測試代碼

#define rightMotorPWMPin   5
#define rightMotorDirPin   4
#define leftMotorPWMPin   6
#define leftMotorDirPin   7

int output = 200;

void Forward() //Code to rotate the wheel forward 
{
    digitalWrite(rightMotorDirPin, 1);
    digitalWrite(leftMotorDirPin, 1);
    analogWrite(rightMotorPWMPin,255-output);
    analogWrite(leftMotorPWMPin,255-output);
    
    Serial.println("FORWARD"); //Debugging information 
}

void Back() //Code to rotate the wheel forward 
{
    digitalWrite(rightMotorDirPin, 0);
    digitalWrite(leftMotorDirPin, 0);
    analogWrite(rightMotorPWMPin,output);
    analogWrite(leftMotorPWMPin,output);   
    Serial.println("BACK"); //Debugging information 
}

void TrunLeft() //Code to rotate the wheel forward 
{
    digitalWrite(rightMotorDirPin, HIGH);
    analogWrite(rightMotorPWMPin,output);
    analogWrite(leftMotorPWMPin,output);
    digitalWrite(leftMotorDirPin, LOW);
    Serial.println("LEFT"); //Debugging information 
}

void TrunRight() //Code to rotate the wheel forward 
{
    digitalWrite(rightMotorDirPin, LOW);
    analogWrite(rightMotorPWMPin,output);
    analogWrite(leftMotorPWMPin,output);
    digitalWrite(leftMotorDirPin, HIGH);
    Serial.println("LEFT"); //Debugging information 
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(leftMotorPWMPin, OUTPUT);
  pinMode(leftMotorDirPin, OUTPUT);
  pinMode(rightMotorPWMPin, OUTPUT);
  pinMode(rightMotorDirPin, OUTPUT);
 
}

void loop() {

  Forward();
  delay(3000);
  Back();
  delay(3000);
  
  /*

while(Serial.available()>0){

   char teststring = Serial.read();
   if(teststring=='a')
   {
    output=output+5;
    
    if(output>255)
    output=10;
    }

   }
   if(output!=output)
   {
   Serial.println(output);
   }
  Back();
  */
  /*
  while(Serial.available()>0){

   char teststring = Serial.read();

   switch (teststring) {
    case 'F':    
      Serial.println("Move Forward");
      Forward();
      break;
    case 'B':    
      Serial.println("Move Back"); 
      Back(); 
      break;
    case 'L':    
      Serial.println("TrunLeft");
      TrunLeft();
      break;
    case 'R':    
      Serial.println("TrunRight");
      TrunRight();
      break;
  }
    Serial.println(teststring);

   delay(1000); 
   
  
 
  }*/
}

3.MPU6050座標軸

繞X軸旋轉roll，橫滾軸
繞Y軸旋轉pitch，俯仰軸
繞Z軸旋轉yaw，偏航角
這裏採用的是Y軸與前後運動方向平行的安裝方式，不一致的話，代碼一改的代碼量有點多，代碼二改個數組就行。

4.MPU6050校準

// MPU6050 offset-finder, based on Jeff Rowberg's MPU6050_RAW
// 2016-10-19 by Robert R. Fenichel ([email protected])

// I2C device class (I2Cdev) demonstration Arduino sketch for MPU6050 class
// 10/7/2011 by Jeff Rowberg <[email protected]>
// Updates should (hopefully) always be available at https://github.com/jrowberg/i2cdevlib
//
// Changelog:
//      2019-07-11 - added PID offset generation at begninning Generates first offsets 
//                 - in @ 6 seconds and completes with 4 more sets @ 10 seconds
//                 - then continues with origional 2016 calibration code.
//      2016-11-25 - added delays to reduce sampling rate to ~200 Hz
//                   added temporizing printing during long computations
//      2016-10-25 - requires inequality (Low < Target, High > Target) during expansion
//                   dynamic speed change when closing in
//      2016-10-22 - cosmetic changes
//      2016-10-19 - initial release of IMU_Zero
//      2013-05-08 - added multiple output formats
//                 - added seamless Fastwire support
//      2011-10-07 - initial release of MPU6050_RAW

/* ============================================
I2Cdev device library code is placed under the MIT license
Copyright (c) 2011 Jeff Rowberg

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

  If an MPU6050 
      * is an ideal member of its tribe, 
      * is properly warmed up, 
      * is at rest in a neutral position, 
      * is in a location where the pull of gravity is exactly 1g, and 
      * has been loaded with the best possible offsets, 
then it will report 0 for all accelerations and displacements, except for 
Z acceleration, for which it will report 16384 (that is, 2^14).  Your device 
probably won't do quite this well, but good offsets will all get the baseline 
outputs close to these target values.

  Put the MPU6050 on a flat and horizontal surface, and leave it operating for 
5-10 minutes so its temperature gets stabilized.

  Run this program.  A "----- done -----" line will indicate that it has done its best.
With the current accuracy-related constants (NFast = 1000, NSlow = 10000), it will take 
a few minutes to get there.

  Along the way, it will generate a dozen or so lines of output, showing that for each 
of the 6 desired offsets, it is 
      * first, trying to find two estimates, one too low and one too high, and
      * then, closing in until the bracket can't be made smaller.

  The line just above the "done" line will look something like
    [567,567] --> [-1,2]  [-2223,-2223] --> [0,1] [1131,1132] --> [16374,16404] [155,156] --> [-1,1]  [-25,-24] --> [0,3] [5,6] --> [0,4]
As will have been shown in interspersed header lines, the six groups making up this
line describe the optimum offsets for the X acceleration, Y acceleration, Z acceleration,
X gyro, Y gyro, and Z gyro, respectively.  In the sample shown just above, the trial showed
that +567 was the best offset for the X acceleration, -2223 was best for Y acceleration, 
and so on.

  The need for the delay between readings (usDelay) was brought to my attention by Nikolaus Doppelhammer.
===============================================
*/

// I2Cdev and MPU6050 must be installed as libraries, or else the .cpp/.h files
// for both classes must be in the include path of your project
#include "I2Cdev.h"
#include "MPU6050.h"

// Arduino Wire library is required if I2Cdev I2CDEV_ARDUINO_WIRE implementation
// is used in I2Cdev.h
#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
    #include "Wire.h"
#endif

// class default I2C address is 0x68
// specific I2C addresses may be passed as a parameter here
// AD0 low = 0x68 (default for InvenSense evaluation board)
// AD0 high = 0x69
MPU6050 accelgyro;
//MPU6050 accelgyro(0x69); // <-- use for AD0 high


const char LBRACKET = '[';
const char RBRACKET = ']';
const char COMMA    = ',';
const char BLANK    = ' ';
const char PERIOD   = '.';

const int iAx = 0;
const int iAy = 1;
const int iAz = 2;
const int iGx = 3;
const int iGy = 4;
const int iGz = 5;

const int usDelay = 3150;   // empirical, to hold sampling to 200 Hz
const int NFast =  1000;    // the bigger, the better (but slower)
const int NSlow = 10000;    // ..
const int LinesBetweenHeaders = 5;
      int LowValue[6];
      int HighValue[6];
      int Smoothed[6];
      int LowOffset[6];
      int HighOffset[6];
      int Target[6];
      int LinesOut;
      int N;
      
void ForceHeader()
  { LinesOut = 99; }
    
void GetSmoothed()
  { int16_t RawValue[6];
    int i;
    long Sums[6];
    for (i = iAx; i <= iGz; i++)
      { Sums[i] = 0; }
//    unsigned long Start = micros();

    for (i = 1; i <= N; i++)
      { // get sums
        accelgyro.getMotion6(&RawValue[iAx], &RawValue[iAy], &RawValue[iAz], 
                             &RawValue[iGx], &RawValue[iGy], &RawValue[iGz]);
        if ((i % 500) == 0)
          Serial.print(PERIOD);
        delayMicroseconds(usDelay);
        for (int j = iAx; j <= iGz; j++)
          Sums[j] = Sums[j] + RawValue[j];
      } // get sums
//    unsigned long usForN = micros() - Start;
//    Serial.print(" reading at ");
//    Serial.print(1000000/((usForN+N/2)/N));
//    Serial.println(" Hz");
    for (i = iAx; i <= iGz; i++)
      { Smoothed[i] = (Sums[i] + N/2) / N ; }
  } // GetSmoothed

void Initialize()
  {
    // join I2C bus (I2Cdev library doesn't do this automatically)
    #if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE
        Wire.begin();
    #elif I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_FASTWIRE
        Fastwire::setup(400, true);
    #endif

    Serial.begin(9600);

    // initialize device
    Serial.println("Initializing I2C devices...");
    accelgyro.initialize();

    // verify connection
    Serial.println("Testing device connections...");
    Serial.println(accelgyro.testConnection() ? "MPU6050 connection successful" : "MPU6050 connection failed");
    Serial.println("PID tuning Each Dot = 100 readings");
  /*A tidbit on how PID (PI actually) tuning works. 
    When we change the offset in the MPU6050 we can get instant results. This allows us to use Proportional and 
    integral of the PID to discover the ideal offsets. Integral is the key to discovering these offsets, Integral 
    uses the error from set-point (set-point is zero), it takes a fraction of this error (error * ki) and adds it 
    to the integral value. Each reading narrows the error down to the desired offset. The greater the error from 
    set-point, the more we adjust the integral value. The proportional does its part by hiding the noise from the 
    integral math. The Derivative is not used because of the noise and because the sensor is stationary. With the 
    noise removed the integral value lands on a solid offset after just 600 readings. At the end of each set of 100 
    readings, the integral value is used for the actual offsets and the last proportional reading is ignored due to 
    the fact it reacts to any noise.
  */
        accelgyro.CalibrateAccel(6);
        accelgyro.CalibrateGyro(6);
        Serial.println("\nat 600 Readings");
        accelgyro.PrintActiveOffsets();
        Serial.println();
        accelgyro.CalibrateAccel(1);
        accelgyro.CalibrateGyro(1);
        Serial.println("700 Total Readings");
        accelgyro.PrintActiveOffsets();
        Serial.println();
        accelgyro.CalibrateAccel(1);
        accelgyro.CalibrateGyro(1);
        Serial.println("800 Total Readings");
        accelgyro.PrintActiveOffsets();
        Serial.println();
        accelgyro.CalibrateAccel(1);
        accelgyro.CalibrateGyro(1);
        Serial.println("900 Total Readings");
        accelgyro.PrintActiveOffsets();
        Serial.println();    
        accelgyro.CalibrateAccel(1);
        accelgyro.CalibrateGyro(1);
        Serial.println("1000 Total Readings");
        accelgyro.PrintActiveOffsets();
     Serial.println("\n\n Any of the above offsets will work nice \n\n Lets proof the PID tuning using another method:"); 
  } // Initialize

void SetOffsets(int TheOffsets[6])
  { accelgyro.setXAccelOffset(TheOffsets [iAx]);
    accelgyro.setYAccelOffset(TheOffsets [iAy]);
    accelgyro.setZAccelOffset(TheOffsets [iAz]);
    accelgyro.setXGyroOffset (TheOffsets [iGx]);
    accelgyro.setYGyroOffset (TheOffsets [iGy]);
    accelgyro.setZGyroOffset (TheOffsets [iGz]);
  } // SetOffsets

void ShowProgress()
  { if (LinesOut >= LinesBetweenHeaders)
      { // show header
        Serial.println("\tXAccel\t\t\tYAccel\t\t\t\tZAccel\t\t\tXGyro\t\t\tYGyro\t\t\tZGyro");
        LinesOut = 0;
      } // show header
    Serial.print(BLANK);
    for (int i = iAx; i <= iGz; i++)
      { Serial.print(LBRACKET);
        Serial.print(LowOffset[i]),
        Serial.print(COMMA);
        Serial.print(HighOffset[i]);
        Serial.print("] --> [");
        Serial.print(LowValue[i]);
        Serial.print(COMMA);
        Serial.print(HighValue[i]);
        if (i == iGz)
          { Serial.println(RBRACKET); }
        else
          { Serial.print("]\t"); }
      }
    LinesOut++;
  } // ShowProgress

void PullBracketsIn()
  { boolean AllBracketsNarrow;
    boolean StillWorking;
    int NewOffset[6];
  
    Serial.println("\nclosing in:");
    AllBracketsNarrow = false;
    ForceHeader();
    StillWorking = true;
    while (StillWorking) 
      { StillWorking = false;
        if (AllBracketsNarrow && (N == NFast))
          { SetAveraging(NSlow); }
        else
          { AllBracketsNarrow = true; }// tentative
        for (int i = iAx; i <= iGz; i++)
          { if (HighOffset[i] <= (LowOffset[i]+1))
              { NewOffset[i] = LowOffset[i]; }
            else
              { // binary search
                StillWorking = true;
                NewOffset[i] = (LowOffset[i] + HighOffset[i]) / 2;
                if (HighOffset[i] > (LowOffset[i] + 10))
                  { AllBracketsNarrow = false; }
              } // binary search
          }
        SetOffsets(NewOffset);
        GetSmoothed();
        for (int i = iAx; i <= iGz; i++)
          { // closing in
            if (Smoothed[i] > Target[i])
              { // use lower half
                HighOffset[i] = NewOffset[i];
                HighValue[i] = Smoothed[i];
              } // use lower half
            else
              { // use upper half
                LowOffset[i] = NewOffset[i];
                LowValue[i] = Smoothed[i];
              } // use upper half
          } // closing in
        ShowProgress();
      } // still working
   
  } // PullBracketsIn

void PullBracketsOut()
  { boolean Done = false;
    int NextLowOffset[6];
    int NextHighOffset[6];

    Serial.println("expanding:");
    ForceHeader();
 
    while (!Done)
      { Done = true;
        SetOffsets(LowOffset);
        GetSmoothed();
        for (int i = iAx; i <= iGz; i++)
          { // got low values
            LowValue[i] = Smoothed[i];
            if (LowValue[i] >= Target[i])
              { Done = false;
                NextLowOffset[i] = LowOffset[i] - 1000;
              }
            else
              { NextLowOffset[i] = LowOffset[i]; }
          } // got low values
      
        SetOffsets(HighOffset);
        GetSmoothed();
        for (int i = iAx; i <= iGz; i++)
          { // got high values
            HighValue[i] = Smoothed[i];
            if (HighValue[i] <= Target[i])
              { Done = false;
                NextHighOffset[i] = HighOffset[i] + 1000;
              }
            else
              { NextHighOffset[i] = HighOffset[i]; }
          } // got high values
        ShowProgress();
        for (int i = iAx; i <= iGz; i++)
          { LowOffset[i] = NextLowOffset[i];   // had to wait until ShowProgress done
            HighOffset[i] = NextHighOffset[i]; // ..
          }
     } // keep going
  } // PullBracketsOut

void SetAveraging(int NewN)
  { N = NewN;
    Serial.print("averaging ");
    Serial.print(N);
    Serial.println(" readings each time");
   } // SetAveraging

void setup()
  { Initialize();
    for (int i = iAx; i <= iGz; i++)
      { // set targets and initial guesses
        Target[i] = 0; // must fix for ZAccel 
        HighOffset[i] = 0;
        LowOffset[i] = 0;
      } // set targets and initial guesses
    Target[iAz] = 16384;
    SetAveraging(NFast);
    
    PullBracketsOut();
    PullBracketsIn();
    
    Serial.println("-------------- done --------------");
  } // setup
 
void loop()
  {
  } // loop

5.代碼一

//原代碼有超聲波測距功能，我把這部分功能註釋掉了
#include "Wire.h"
#include "I2Cdev.h"
#include "MPU6050.h"
#include "math.h"
//#include <NewPing.h>
#define leftMotorPWMPin   6
#define leftMotorDirPin   7
#define rightMotorPWMPin  5
#define rightMotorDirPin  4
//#define TRIGGER_PIN 9
//#define ECHO_PIN 8
//#define MAX_DISTANCE 75
#define Kp  120
#define Kd  0.15
#define Ki  120
#define sampleTime  0.005
#define targetAngle -2.5
MPU6050 mpu;
//NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);
int16_t accY, accZ, gyroX;
volatile int motorPower, gyroRate;
volatile float accAngle, gyroAngle, currentAngle, prevAngle=0, error, prevError=0, errorSum=0;
volatile byte count=0;
//int distanceCm;
//setMotors()裏面leftMotorSpeed >= 0兩句是同時成立，所以只有直立環，沒有轉向環
void setMotors(int leftMotorSpeed, int rightMotorSpeed) {
  if(leftMotorSpeed >= 0) {
    analogWrite(leftMotorPWMPin, leftMotorSpeed);
    digitalWrite(leftMotorDirPin, LOW);
  }
  else {
    analogWrite(leftMotorPWMPin, 255 + leftMotorSpeed);
    digitalWrite(leftMotorDirPin, HIGH);
  }
  if(rightMotorSpeed >= 0) {
    analogWrite(rightMotorPWMPin, rightMotorSpeed);
    digitalWrite(rightMotorDirPin, LOW);
  }
  else {
    analogWrite(rightMotorPWMPin, 255 + rightMotorSpeed);
    digitalWrite(rightMotorDirPin, HIGH);
  }
}
void init_PID() {  
  // initialize Timer1
  cli();          // disable global interrupts
  TCCR1A = 0;     // set entire TCCR1A register to 0
  TCCR1B = 0;     // same for TCCR1B    
  // set compare match register to set sample time 5ms
  OCR1A = 9999;    
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS11 bit for prescaling by 8
  TCCR1B |= (1 << CS11);
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);
  sei();          // enable global interrupts
}
void setup() {
  // set the motor control and PWM pins to output mode
  pinMode(leftMotorPWMPin, OUTPUT);
  pinMode(leftMotorDirPin, OUTPUT);
  pinMode(rightMotorPWMPin, OUTPUT);
  pinMode(rightMotorDirPin, OUTPUT);
  // set the status LED to output mode 
  pinMode(13, OUTPUT);
  // initialize the MPU6050 and set offset values
  mpu.initialize();
  mpu.setYAccelOffset(1810);
  mpu.setZAccelOffset(858);
  mpu.setXGyroOffset(-332);
  // initialize PID sampling loop
  init_PID();
}
void loop() {
  // read acceleration and gyroscope values
  accY = mpu.getAccelerationY();
  accZ = mpu.getAccelerationZ();  
  gyroX = mpu.getRotationX();
  // set motor power after constraining it
  motorPower = constrain(motorPower, -255, 255);
  setMotors(motorPower, motorPower);
  // measure distance every 100 milliseconds
  /*if((count%20) == 0){
    distanceCm = sonar.ping_cm();
  }
  if((distanceCm < 20) && (distanceCm != 0)) {
    setMotors(-motorPower, motorPower);
  }*/
}
// The ISR will be called every 5 milliseconds
ISR(TIMER1_COMPA_vect)
{
  // calculate the angle of inclination
  accAngle = atan2(accY, accZ)*RAD_TO_DEG;
  gyroRate = map(gyroX, -32768, 32767, -250, 250);
  gyroAngle = (float)gyroRate*sampleTime;  
  currentAngle = 0.9934*(prevAngle + gyroAngle) + 0.0066*(accAngle);
  
  error = currentAngle - targetAngle;
  errorSum = errorSum + error;  
  errorSum = constrain(errorSum, -300, 300);
  //calculate output from P, I and D values
  motorPower = Kp*(error) + Ki*(errorSum)*sampleTime - Kd*(currentAngle-prevAngle)/sampleTime;
  prevAngle = currentAngle;
  // toggle the led on pin13 every second
  count++;
  if(count == 200)  {
    count = 0;
    digitalWrite(13, !digitalRead(13));
  }
}

6.代碼二

/*Arduino Self Balancing Robot
 * Code by: B.Aswinth Raj
 * Build on top of Lib: https://github.com/jrowberg/i2cdevlib/tree/master/Arduino/MPU6050
 * Website: circuitdigest.com 
 */

#include "I2Cdev.h"
#include <PID_v1.h> //From https://github.com/br3ttb/Arduino-PID-Library/blob/master/PID_v1.h
#include "MPU6050_6Axis_MotionApps20.h" //https://github.com/jrowberg/i2cdevlib/tree/master/Arduino/MPU6050

MPU6050 mpu(0x68);

#define INTERRUPT_PIN 2  // use pin 2 on Arduino Uno & most boards
#define LED_PIN 13 // (Arduino is 13, Teensy is 11, Teensy++ is 6)

bool blinkState = false;

// MPU control/status vars
bool dmpReady = false;  // set true if DMP init was successful
uint8_t mpuIntStatus;   // holds actual interrupt status byte from MPU
uint8_t devStatus;      // return status after each device operation (0 = success, !0 = error)
uint16_t packetSize;    // expected DMP packet size (default is 42 bytes)
uint16_t fifoCount;     // count of all bytes currently in FIFO
uint8_t fifoBuffer[64]; // FIFO storage buffer

// orientation/motion vars
Quaternion q;           // [w, x, y, z]         quaternion container
VectorFloat gravity;    // [x, y, z]            gravity vector
float ypr[3];           // [yaw, pitch, roll]   yaw/pitch/roll container and gravity vector

/*********Tune these 4 values for your BOT*********/
double setpoint= 180; //set the value when the bot is perpendicular to ground using serial monitor. 
//Read the project documentation on circuitdigest.com to learn how to set these values
double Kp = 42; //Set this first
double Kd = 0; //Set this secound
double Ki = 0; //Finally set this 
/******End of values setting*********/

double input, output;
PID pid(&input, &output, &setpoint, Kp, Ki, Kd, DIRECT);

volatile bool mpuInterrupt = false;     // indicates whether MPU interrupt pin has gone high
void dmpDataReady()
{
    mpuInterrupt = true;
}

void setup() {
  Serial.begin(115200);

  // initialize device
    Serial.println(F("Initializing I2C devices..."));
    mpu.initialize();

     // verify connection
    Serial.println(F("Testing device connections..."));
    Serial.println(mpu.testConnection() ? F("MPU6050 connection successful") : F("MPU6050 connection failed"));

    // load and configure the DMP
    devStatus = mpu.dmpInitialize();

    
    // supply your own gyro offsets here, scaled for min sensitivity
    mpu.setXGyroOffset(-332);
    mpu.setYGyroOffset(-18);
    mpu.setZGyroOffset(-34);
    //mpu.setXAccelOffset(115); 
    //mpu.setYAccelOffset(1810); 
    mpu.setZAccelOffset(858); 
      // make sure it worked (returns 0 if so)
    if (devStatus == 0)
    {
        // turn on the DMP, now that it's ready
        mpu.CalibrateAccel(6);
        mpu.CalibrateGyro(6);
        Serial.println();
        mpu.PrintActiveOffsets();
        Serial.println(F("Enabling DMP..."));
        mpu.setDMPEnabled(true);

        // enable Arduino interrupt detection
        Serial.println(F("Enabling interrupt detection (Arduino external interrupt 0)..."));
        attachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN), dmpDataReady, RISING);
        mpuIntStatus = mpu.getIntStatus();

        // set our DMP Ready flag so the main loop() function knows it's okay to use it
        Serial.println(F("DMP ready! Waiting for first interrupt..."));
        dmpReady = true;

        // get expected DMP packet size for later comparison
        packetSize = mpu.dmpGetFIFOPacketSize();
        
        //setup PID
        pid.SetMode(AUTOMATIC);
        pid.SetSampleTime(10);
        pid.SetOutputLimits(-255, 255);  
    }
    else
    {
        // ERROR!
        // 1 = initial memory load failed
        // 2 = DMP configuration updates failed
        // (if it's going to break, usually the code will be 1)
        Serial.print(F("DMP Initialization failed (code "));
        Serial.print(devStatus);
        Serial.println(F(")"));
    }

//Initialise the Motor outpu pins
    pinMode (4, OUTPUT);
    pinMode (5, OUTPUT);
    pinMode (6, OUTPUT);
    pinMode (7, OUTPUT);
    pinMode(LED_PIN, OUTPUT);

}

void loop() {
 
    // if programming failed, don't try to do anything
    if (!dmpReady) return;

    // wait for MPU interrupt or extra packet(s) available
    while (!mpuInterrupt && fifoCount < packetSize)
    {
        digitalWrite(LED_PIN,LOW);
        //no mpu data - performing PID calculations and output to motors     
        pid.Compute();   
        
        //Print the value of Input and Output on serial monitor to check how it is working.
        Serial.print(input); Serial.print(" =>"); Serial.println(output);
               
        if (input>150 && input<200){//If the Bot is falling 
          
        if (output>0) //Falling towards front 
        Forward(); //Rotate the wheels forward 
        else if (output<0) //Falling towards back
        Reverse(); //Rotate the wheels backward 
        }
        else //If Bot not falling
        Stop(); //Hold the wheels still
        digitalWrite(LED_PIN,HIGH);
        
    }

    // reset interrupt flag and get INT_STATUS byte
    mpuInterrupt = false;
    mpuIntStatus = mpu.getIntStatus();

    // get current FIFO count
    fifoCount = mpu.getFIFOCount();

    // check for overflow (this should never happen unless our code is too inefficient)
    if ((mpuIntStatus & 0x10) || fifoCount == 1024)
    {
        // reset so we can continue cleanly
        mpu.resetFIFO();
        Serial.println(F("FIFO overflow!"));
        digitalWrite(LED_PIN,HIGH);

    // otherwise, check for DMP data ready interrupt (this should happen frequently)
    }
    else if (mpuIntStatus & 0x02)
    {
        // wait for correct available data length, should be a VERY short wait
        while (fifoCount < packetSize) fifoCount = mpu.getFIFOCount();

        // read a packet from FIFO
        mpu.getFIFOBytes(fifoBuffer, packetSize);
        
        // track FIFO count here in case there is > 1 packet available
        // (this lets us immediately read more without waiting for an interrupt)
        fifoCount -= packetSize;

        mpu.dmpGetQuaternion(&q, fifoBuffer); //get value for q
        mpu.dmpGetGravity(&gravity, &q); //get value for gravity
        mpu.dmpGetYawPitchRoll(ypr, &q, &gravity); //get value for ypr
        //memset(fifoBuffer, 0, sizeof fifoBuffer); 

        input = ypr[2] * 180/M_PI + 180;             //根據你的安裝方式及前面的定義，改ypr[2]這個數組就可以。
        

   }
}

void Reverse() //Code to rotate the wheel forward 
{
    digitalWrite(4,LOW);
    digitalWrite(7,LOW);
    analogWrite(5,output);
    analogWrite(6,output); 
    Serial.println("R"); //Debugging information 
}

void Forward() //Code to rotate the wheel Backward  
{
    digitalWrite(4,HIGH);
    digitalWrite(7,HIGH); 
    analogWrite(5,-output);
    analogWrite(6,-output);
    Serial.println("F");
}

void Stop() //Code to stop both the wheels
{
    digitalWrite(4,0);
    digitalWrite(7,0); 
    analogWrite(5,0);
    analogWrite(6,0);  
    Serial.println("S");
}

7.總結

根據實際測試的情況來看，代碼一的效果較爲穩定。
參考鏈接