Bonjour,

Je dois créer une station météo connectée via Arduino et un capteur MPL3115A2.
J'ai réussi à obtenir une température correcte cependant le problème est dans l'initialisation du capteur.
En effet, j'habite dans une région élevée pour cela je dois initialiser l'altitude ou la pression (je ne sais pas encore) afin d'avoir une pression ainsi qu'une altitude correcte.

Voici mon code :

/*

MPL3115A2 Altitude Sensor One Shot Mode Example
Henry Lahr, 2013-02-27
There is no warranty for this code; feel free to use this code for your projects.
Hardware Connections: VCC = 3.3V; SDA = A4; SCL = A5; INT pins not connected
Usage:
- Serial terminal at 115200bps
- Prints altitude in meters or temperature in degrees C, depending on whether ALTMODE is defined
*/

#include <Wire.h> // for I2C communication

#define ALTMODE; //comment out for barometer mode; default is altitude mode
#define ALTBASIS 18 //start altitude to calculate mean sea level pressure in meters
//this altitude must be known (or provided by GPS etc.)

const int SENSORADDRESS = 0x60; // address specific to the MPL3115A1, value found in datasheet

float altsmooth = 0; //for exponential smoothing
byte IICdata[5] = {0,0,0,0,0}; //buffer for sensor data

void setup(){
  Wire.begin(); // join i2c bus
  Serial.begin(115200); // start serial for output
  Serial.println("Setup");
  if(IIC_Read(0x0C) == 196); //checks whether sensor is readable (who_am_i bit)
  else Serial.println("i2c bad");

  IIC_Write(0x2D,0); //write altitude offset=0 (because calculation below is based on offset=0)
  //calculate sea level pressure by averaging a few readings
  Serial.println("Pressure calibration...");
  float buff[4];
  for (byte i=0;i<4;i++){
    IIC_Write(0x26, 0b00111011); //bit 2 is one shot mode, bits 4-6 are 128x oversampling
    IIC_Write(0x26, 0b00111001); //must clear oversampling (OST) bit, otherwise update will be once per second
    delay(550); //wait for sensor to read pressure (512ms in datasheet)
    IIC_ReadData(); //read sensor data
    buff[i] = Baro_Read(); //read pressure
    Serial.println(buff[i]);
  }
  float currpress=(buff[0]+buff[1]+buff[2]+buff[3])/4; //average over two seconds

  Serial.print("Current pressure: "); Serial.print(currpress); Serial.println(" Pa");
  //calculate pressure at mean sea level based on a given altitude
  float seapress = currpress/pow(1-ALTBASIS*0.0000225577,5.255877);
  Serial.print("Sea level pressure: "); Serial.print(seapress); Serial.println(" Pa");
  Serial.print("Temperature: ");
  Serial.print(IICdata[3]+(float)(IICdata[4]>>4)/16); Serial.println(" C");

  // This configuration option calibrates the sensor according to
  // the sea level pressure for the measurement location (2 Pa per LSB)
  IIC_Write(0x14, (unsigned int)(seapress / 2)>>8);//IIC_Write(0x14, 0xC3); // BAR_IN_MSB (register 0x14):
  IIC_Write(0x15, (unsigned int)(seapress / 2)&0xFF);//IIC_Write(0x15, 0xF3); // BAR_IN_LSB (register 0x15):

  //one reading seems to take 4ms (datasheet p.33);
  //oversampling 32x=130ms interval between readings seems to be best for 10Hz; slightly too slow
  //first bit is altitude mode (vs. barometer mode)

  //Altitude mode
  IIC_Write(0x26, 0b10111011); //bit 2 is one shot mode //0xB9 = 0b10111001
  IIC_Write(0x26, 0b10111001); //must clear oversampling (OST) bit, otherwise update will be once per second
  delay(550); //wait for measurement
  IIC_ReadData(); //
  altsmooth=Alt_Read();
  Serial.print("Altitude now: "); Serial.println(altsmooth);
  Serial.println("Done.");
}

void loop(){
  sensor_read_data();
  // your code here
}

void sensor_read_data(){
  // This function reads the altitude (or barometer) and temperature registers, then prints their values
  // variables for the calculations
  int m_temp;
  float l_temp;
  float altbaro, temperature;

  //One shot mode at 0b10101011 is slightly too fast, but better than wasting sensor cycles that increase precision
  //one reading seems to take 4ms (datasheet p.33);
  //oversampling at 32x=130ms interval between readings seems to be optimal for 10Hz
  #ifdef ALTMODE //Altitude mode
    IIC_Write(0x26, 0b10111011); //bit 2 is one shot mode //0xB9 = 0b10111001
    IIC_Write(0x26, 0b10111001); //must clear oversampling (OST) bit, otherwise update will be once per second
  #else //Barometer mode
    IIC_Write(0x26, 0b00111011); //bit 2 is one shot mode //0xB9 = 0b10111001
    IIC_Write(0x26, 0b00111001); //must clear oversampling (OST) bit, otherwise update will be once per second
  #endif
  delay(1000); //read with 10Hz; drop this if calling from an outer loop

  IIC_ReadData(); //reads registers from the sensor
  m_temp = IICdata[3]; //temperature, degrees
  l_temp = (float)(IICdata[4]>>4)/16.0; //temperature, fraction of a degree
  temperature = (float)(m_temp + l_temp);

  #ifdef ALTMODE //converts byte data into float; change function to Alt_Read() or Baro_Read()
    altbaro = Alt_Read();
  #else
    altbaro = Baro_Read();
  #endif

  altsmooth=(altsmooth*3+altbaro)/4; //exponential smoothing to get a smooth time series

  Serial.println("Pressure and Altitude");
  Serial.print(altbaro); // in meters or Pascal
  Serial.print(",");
  Serial.print(altsmooth); // exponentially smoothed
  Serial.print(",");
  Serial.println("Temperature");
  Serial.println(temperature); // in degrees C
}

float Baro_Read(){
  //this function takes values from the read buffer and converts them to pressure units
  unsigned long m_altitude = IICdata[0];
  unsigned long c_altitude = IICdata[1];
  float l_altitude = (float)(IICdata[2]>>4)/4; //dividing by 4, since two lowest bits are fractional value
  return((float)(m_altitude<<10 | c_altitude<<2)+l_altitude); //shifting 2 to the left to make room for LSB
}

float Alt_Read(){
  //Reads altitude data (if CTRL_REG1 is set to altitude mode)
  int m_altitude = IICdata[0];
  int c_altitude = IICdata[1];
  float l_altitude = (float)(IICdata[2]>>4)/16;
  return((float)((m_altitude << 8)|c_altitude) + l_altitude);
}

byte IIC_Read(byte regAddr){
  // This function reads one byte over I2C
  Wire.beginTransmission(SENSORADDRESS);
  Wire.write(regAddr); // Address of CTRL_REG1
  Wire.endTransmission(false); // Send data to I2C dev with option for a repeated start. Works in Arduino V1.0.1
  Wire.requestFrom(SENSORADDRESS, 1);
  return Wire.read();
}

void IIC_ReadData(){  //Read Altitude/Barometer and Temperature data (5 bytes)
  //This is faster than reading individual register, as the sensor automatically increments the register address,
  //so we just keep reading...
  byte i=0;
  Wire.beginTransmission(SENSORADDRESS);
  Wire.write(0x01); // Address of CTRL_REG1
  Wire.endTransmission(false);
  Wire.requestFrom(SENSORADDRESS,5); //read 5 bytes: 3 for altitude or pressure, 2 for temperature
  while(Wire.available()) IICdata[i++] = Wire.read();
}

void IIC_Write(byte regAddr, byte value){
  // This function writes one byto over I2C
  Wire.beginTransmission(SENSORADDRESS);
  Wire.write(regAddr);
  Wire.write(value);
  Wire.endTransmission(true);
  }

Si vous avez une idée de comment modifier le code afin de calibrer mon capteur.

Je vous remercie d'avance de votre réponse.

Claire

Edit Coll : forum modifié ; initialement posté au niveau supérieur-École d'ingénieurs