Parts list:
Arduino board
LCD 16×2
Gyroscope MPU-6050
Potentiometer 10K
Resistor 220 ohm
Breadbord
Connecting wire

Wiring:

Video:

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);

#include <Wire.h>

//Declaring some global variables
int gyro_x, gyro_y, gyro_z;
long acc_x, acc_y, acc_z, acc_total_vector;
int temperature;
long gyro_x_cal, gyro_y_cal, gyro_z_cal;
long loop_timer;
int lcd_loop_counter;
float angle_pitch, angle_roll;
int angle_pitch_buffer, angle_roll_buffer;
boolean set_gyro_angles;
float angle_roll_acc, angle_pitch_acc;
float angle_pitch_output, angle_roll_output;

//Initialize the LCD library
//LiquidCrystal_I2C lcd(0x27,16,2);

void setup() {
Wire.begin();                                                        //Start I2C as master
//Serial.begin(57600);                                               //Use only for debugging
pinMode(13, OUTPUT);                                                 //Set output 13 (LED) as output

setup_mpu_6050_registers();                                          //Setup the registers of the MPU-6050 (500dfs / +/-8g) and start the gyro

digitalWrite(13, HIGH);                                              //Set digital output 13 high to indicate startup

lcd.begin(16, 2);  //LCD order

lcd.setCursor(0,0);                                                  //Set the LCD cursor to position to position 0,0
lcd.print(“Spirit Level”);                                         //Print text to screen
lcd.setCursor(0,1);                                                  //Set the LCD cursor to position to position 0,1
lcd.print(”     V1.0″);                                              //Print text to screen

delay(1500);                                                         //Delay 1.5 second to display the text
lcd.clear();                                                         //Clear the LCD

lcd.setCursor(0,0);                                                  //Set the LCD cursor to position to position 0,0
lcd.print(“Calibrating gyro”);                                       //Print text to screen
lcd.setCursor(0,1);                                                  //Set the LCD cursor to position to position 0,1
for (int cal_int = 0; cal_int < 2000 ; cal_int ++){                  //Run this code 2000 times
if(cal_int % 125 == 0)lcd.print(“.”);                              //Print a dot on the LCD every 125 readings
read_mpu_6050_data();                                              //Read the raw acc and gyro data from the MPU-6050
gyro_x_cal += gyro_x;                                              //Add the gyro x-axis offset to the gyro_x_cal variable
gyro_y_cal += gyro_y;                                              //Add the gyro y-axis offset to the gyro_y_cal variable
gyro_z_cal += gyro_z;                                              //Add the gyro z-axis offset to the gyro_z_cal variable
delay(3);                                                          //Delay 3us to simulate the 250Hz program loop
}
gyro_x_cal /= 2000;                                                  //Divide the gyro_x_cal variable by 2000 to get the avarage offset
gyro_y_cal /= 2000;                                                  //Divide the gyro_y_cal variable by 2000 to get the avarage offset
gyro_z_cal /= 2000;                                                  //Divide the gyro_z_cal variable by 2000 to get the avarage offset

lcd.clear();                                                         //Clear the LCD

lcd.setCursor(0,0);                                                  //Set the LCD cursor to position to position 0,0
lcd.print(“Pitch:”);                                                 //Print text to screen
lcd.setCursor(0,1);                                                  //Set the LCD cursor to position to position 0,1
lcd.print(“Roll :”);                                                 //Print text to screen

digitalWrite(13, LOW);                                               //All done, turn the LED off

loop_timer = micros();                                               //Reset the loop timer
}

void loop(){

read_mpu_6050_data();                                                //Read the raw acc and gyro data from the MPU-6050

gyro_x -= gyro_x_cal;                                                //Subtract the offset calibration value from the raw gyro_x value
gyro_y -= gyro_y_cal;                                                //Subtract the offset calibration value from the raw gyro_y value
gyro_z -= gyro_z_cal;                                                //Subtract the offset calibration value from the raw gyro_z value

//Gyro angle calculations
//0.0000611 = 1 / (250Hz / 65.5)
angle_pitch += gyro_x * 0.0000611;                                   //Calculate the traveled pitch angle and add this to the angle_pitch variable
angle_roll += gyro_y * 0.0000611;                                    //Calculate the traveled roll angle and add this to the angle_roll variable

//0.000001066 = 0.0000611 * (3.142(PI) / 180degr) The Arduino sin function is in radians
angle_pitch += angle_roll * sin(gyro_z * 0.000001066);               //If the IMU has yawed transfer the roll angle to the pitch angel
angle_roll -= angle_pitch * sin(gyro_z * 0.000001066);               //If the IMU has yawed transfer the pitch angle to the roll angel

//Accelerometer angle calculations
acc_total_vector = sqrt((acc_x*acc_x)+(acc_y*acc_y)+(acc_z*acc_z));  //Calculate the total accelerometer vector
//57.296 = 1 / (3.142 / 180) The Arduino asin function is in radians
angle_pitch_acc = asin((float)acc_y/acc_total_vector)* 57.296;       //Calculate the pitch angle
angle_roll_acc = asin((float)acc_x/acc_total_vector)* -57.296;       //Calculate the roll angle

//Place the MPU-6050 spirit level and note the values in the following two lines for calibration
angle_pitch_acc -= 0.0;                                              //Accelerometer calibration value for pitch
angle_roll_acc -= 0.0;                                               //Accelerometer calibration value for roll

if(set_gyro_angles){                                                 //If the IMU is already started
angle_pitch = angle_pitch * 0.9996 + angle_pitch_acc * 0.0004;     //Correct the drift of the gyro pitch angle with the accelerometer pitch angle
angle_roll = angle_roll * 0.9996 + angle_roll_acc * 0.0004;        //Correct the drift of the gyro roll angle with the accelerometer roll angle
}
else{                                                                //At first start
angle_pitch = angle_pitch_acc;                                     //Set the gyro pitch angle equal to the accelerometer pitch angle
angle_roll = angle_roll_acc;                                       //Set the gyro roll angle equal to the accelerometer roll angle
set_gyro_angles = true;                                            //Set the IMU started flag
}

//To dampen the pitch and roll angles a complementary filter is used
angle_pitch_output = angle_pitch_output * 0.9 + angle_pitch * 0.1;   //Take 90% of the output pitch value and add 10% of the raw pitch value
angle_roll_output = angle_roll_output * 0.9 + angle_roll * 0.1;      //Take 90% of the output roll value and add 10% of the raw roll value

write_LCD();                                                         //Write the roll and pitch values to the LCD display

while(micros() – loop_timer < 4000);                                 //Wait until the loop_timer reaches 4000us (250Hz) before starting the next loop
loop_timer = micros();                                               //Reset the loop timer
}

void read_mpu_6050_data(){                                             //Subroutine for reading the raw gyro and accelerometer data
Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
Wire.write(0x3B);                                                    //Send the requested starting register
Wire.endTransmission();                                              //End the transmission
Wire.requestFrom(0x68,14);                                           //Request 14 bytes from the MPU-6050
while(Wire.available() < 14);                                        //Wait until all the bytes are received
acc_x = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_x variable
acc_y = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_y variable
acc_z = Wire.read()<<8|Wire.read();                                  //Add the low and high byte to the acc_z variable
temperature = Wire.read()<<8|Wire.read();                            //Add the low and high byte to the temperature variable
gyro_x = Wire.read()<<8|Wire.read();                                 //Add the low and high byte to the gyro_x variable
gyro_y = Wire.read()<<8|Wire.read();                                 //Add the low and high byte to the gyro_y variable
gyro_z = Wire.read()<<8|Wire.read();                                 //Add the low and high byte to the gyro_z variable

}

void write_LCD(){                                                      //Subroutine for writing the LCD
//To get a 250Hz program loop (4us) it’s only possible to write one character per loop
//Writing multiple characters is taking to much time
if(lcd_loop_counter == 14)lcd_loop_counter = 0;                      //Reset the counter after 14 characters
lcd_loop_counter ++;                                                 //Increase the counter
if(lcd_loop_counter == 1){
angle_pitch_buffer = angle_pitch_output * 10;                      //Buffer the pitch angle because it will change
lcd.setCursor(6,0);                                                //Set the LCD cursor to position to position 0,0
}
if(lcd_loop_counter == 2){
if(angle_pitch_buffer < 0)lcd.print(“-“);                          //Print – if value is negative
else lcd.print(“+”);                                               //Print + if value is negative
}
if(lcd_loop_counter == 3)lcd.print(abs(angle_pitch_buffer)/1000);    //Print first number
if(lcd_loop_counter == 4)lcd.print((abs(angle_pitch_buffer)/100)%10);//Print second number
if(lcd_loop_counter == 5)lcd.print((abs(angle_pitch_buffer)/10)%10); //Print third number
if(lcd_loop_counter == 6)lcd.print(“.”);                             //Print decimal point
if(lcd_loop_counter == 7)lcd.print(abs(angle_pitch_buffer)%10);      //Print decimal number

if(lcd_loop_counter == 8){
angle_roll_buffer = angle_roll_output * 10;
lcd.setCursor(6,1);
}
if(lcd_loop_counter == 9){
if(angle_roll_buffer < 0)lcd.print(“-“);                           //Print – if value is negative
else lcd.print(“+”);                                               //Print + if value is negative
}
if(lcd_loop_counter == 10)lcd.print(abs(angle_roll_buffer)/1000);    //Print first number
if(lcd_loop_counter == 11)lcd.print((abs(angle_roll_buffer)/100)%10);//Print second number
if(lcd_loop_counter == 12)lcd.print((abs(angle_roll_buffer)/10)%10); //Print third number
if(lcd_loop_counter == 13)lcd.print(“.”);                            //Print decimal point
if(lcd_loop_counter == 14)lcd.print(abs(angle_roll_buffer)%10);      //Print decimal number
}

void setup_mpu_6050_registers(){
//Activate the MPU-6050
Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
Wire.write(0x6B);                                                    //Send the requested starting register
Wire.write(0x00);                                                    //Set the requested starting register
Wire.endTransmission();                                              //End the transmission
//Configure the accelerometer (+/-8g)
Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
Wire.write(0x1C);                                                    //Send the requested starting register
Wire.write(0x10);                                                    //Set the requested starting register
Wire.endTransmission();                                              //End the transmission
//Configure the gyro (500dps full scale)
Wire.beginTransmission(0x68);                                        //Start communicating with the MPU-6050
Wire.write(0x1B);                                                    //Send the requested starting register
Wire.write(0x08);                                                    //Set the requested starting register
Wire.endTransmission();                                              //End the transmission
}