Wakeup Arduino Uno con interrupt da MPU6050

L'accelerometro MPU6050 (altrimenti conosciuto come Gy-521) ha un pin interrupt che puo' essere programmato per risvegliare una Arduino Uno
Ho semplificato un po' il codice ritrovato a questo link

si possono personalizzare le soglie di attivazione dell'interrupt modificando il valore di MOT_THR e MOT_DUR


-----------------------------------------------------------------------
#include <avr/sleep.h>  
#include <Wire.h>


#define SIGNAL_PATH_RESET  0x68
#define I2C_SLV0_ADDR      0x37
#define ACCEL_CONFIG       0x1C 
#define MOT_THR            0x1F  // Motion detection threshold bits [7:0]
#define MOT_DUR            0x20  // Duration counter threshold for motion interrupt generation, 1 kHz rate, LSB = 1 ms
#define MOT_DETECT_CTRL    0x69
#define INT_ENABLE         0x38
#define WHO_AM_I_MPU6050   0x75 // Should return 0x68
#define INT_STATUS 0x3A
//when nothing connected to AD0 than address is 0x68
#define ADO 0
#if ADO
#define MPU6050_ADDRESS 0x69  // Device address when ADO = 1
#else
#define MPU6050_ADDRESS 0x68  // Device address when ADO = 0
#endif

int wakePin = 2;                 // pin used for waking up  


void wakeUpNow() 
{       
}  


void writeByte(uint8_t address, uint8_t subAddress, uint8_t data)
{
  Wire.begin();
  Wire.beginTransmission(address);  // Initialize the Tx buffer
  Wire.write(subAddress);           // Put slave register address in Tx buffer
  Wire.write(data);                 // Put data in Tx buffer
  Wire.endTransmission();           // Send the Tx buffer
}

uint8_t readByte(uint8_t address, uint8_t subAddress)
{
  uint8_t data;                            // `data` will store the register data   
  Wire.beginTransmission(address);         // Initialize the Tx buffer
  Wire.write(subAddress);                  // Put slave register address in Tx buffer
  Wire.endTransmission(false);             // Send the Tx buffer, but send a restart to keep connection alive
  Wire.requestFrom(address, (uint8_t) 1);  // Read one byte from slave register address 
  data = Wire.read();                      // Fill Rx buffer with result
  return data;                             // Return data read from slave register
}


void setup() 
{  
    Serial.begin(9600);
    writeByte( MPU6050_ADDRESS, 0x6B, 0x00);
    writeByte( MPU6050_ADDRESS, SIGNAL_PATH_RESET, 0x07);//Reset all internal signal paths in the MPU-6050 by writing 0x07 to register 0x68;
    writeByte( MPU6050_ADDRESS, I2C_SLV0_ADDR, 0x20);//write register 0x37 to select how to use the interrupt pin. For an active high, push-pull signal that stays until register (decimal) 58 is read, write 0x20.
    writeByte( MPU6050_ADDRESS, ACCEL_CONFIG, 0x01);//Write register 28 (==0x1C) to set the Digital High Pass Filter, bits 3:0. For example set it to 0x01 for 5Hz. (These 3 bits are grey in the data sheet, but they are used! Leaving them 0 means the filter always outputs 0.)
    writeByte( MPU6050_ADDRESS, MOT_THR, 20);  //Write the desired Motion threshold to register 0x1F (For example, write decimal 20).  
    writeByte( MPU6050_ADDRESS, MOT_DUR, 40 );  //Set motion detect duration to 1  ms; LSB is 1 ms @ 1 kHz rate  
    writeByte( MPU6050_ADDRESS, MOT_DETECT_CTRL, 0x15); //to register 0x69, write the motion detection decrement and a few other settings (for example write 0x15 to set both free-fall and motion decrements to 1 and accelerometer start-up delay to 5ms total by adding 1ms. )   
    writeByte( MPU6050_ADDRESS, INT_ENABLE, 0x40 ); //write register 0x38, bit 6 (0x40), to enable motion detection interrupt.     
    writeByte( MPU6050_ADDRESS, 0x37, 160 ); // now INT pin is active low

    pinMode(2, INPUT);        // sets the digital pin 7 as input
    pinMode(wakePin, INPUT_PULLUP);  // wakePin is pin no. 2
}  

void sleepNow() 
{  
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);    
    sleep_enable();                        
    delay(500);  
    attachInterrupt(0,wakeUpNow, LOW); 
    delay(500);
    sleep_mode();     

     //ritorno da interrupt
     delay(500);

     sleep_disable();         
     delay(500);  
     detachInterrupt(0);   
                                
}  

uint16_t readdata;
void loop() 
{     
      sleepNow();     
      /*readdata = readByte(MPU6050_ADDRESS,0x3A);
      Serial.print(readdata);Serial.print("-");
      readdata = readByte(MPU6050_ADDRESS,0x37);
      Serial.println(readdata);*/
      Serial.println("Movimento registrato");     

}