Arduino_Datalogger.ino

// Dataacquisition and analysis
// by Raphael Nagel
// 10032284 - University of the West of England, Bristol
// Created 24 Januar 2013

// This software contacts the MPL3115A2 barometer via I2C and reads a single barometer value with 20bits
// accuracy. It calculates the averages over a 30 sample long period


#include <I2C.h>
#define CP_OK 1
#define CP_ERROR 0


/*Barometer registers*/
#define baro 0x60
#define OUT_P_MSB  0x01
#define OUT_P_CSB 0x02
#define OUT_P_LSB 0x03
#define CTRL_REG1 0x26 
#define set_OST 0x02
#define set_OST_OS 0x3A

#define Period500Hz 2000

#if 0
/*Temperature Registers - currently not needed*/
char OUT_T_MSB = 0x04;
char OUT_T_LSB = 0x05;  
#endif



unsigned long raw = 0; //the raw input value in binary
unsigned long input[30]; //the 32 word FIFO buffer
unsigned long averaged[2]; //the averaged value
int derivative;
int devav[30];
int output = 0; //the output value after it has been worked - in binary

unsigned int counter = 1;
unsigned int i;
unsigned int delay_val = 1800;
unsigned int time = 0;

/********************FUNCTION PROTOTYPES************************************/
void PrintSignedNumber(unsigned long );
unsigned int SingleBarometerRead(unsigned long *);


/******************** VOID SETUP ******************************************/
void setup()
{
  I2c.begin();        // join i2c bus (address optional for master)
  TWBR = 12;         //set the I2C frequency to 400kHz 
  I2c.pullup(1);
  Serial.begin(9600);  // start serial for output
}


/******************** VOID Loop ******************************************/

void loop()
{

  time = micros(); //store the start time of our reads
  SingleBarometerRead(&raw);


  //30 element FIFO buffer
  for(i = 29;i>=1;i--){
    input[i]=input[i-1];
  }
  input[0] = raw;


  /*************average the output and ************************/

  if(counter <=30){
    output = input[0];  
    PrintSignedNumber(output);
    counter++;

  }
  else{
    averaged[1] = averaged[0];
    averaged[0] = 0;

    for(i = 0;i<30;i++){
      averaged[0] = averaged[0]+input[i];
    }  
    averaged[0] =(unsigned long) (averaged[0]/30);


    /* find the derivative.....*/
    derivative = averaged[1]-averaged[0];




    //30 element FIFO buffer to collect the derivatives 
    for(i = 29;i>=1;i--){
      devav[i]=devav[i-1];
    }
    devav[0] = derivative;

    output = 0;
    for(i = 0;i<30;i++){
      output = output + devav[i];
    }  
    output =(output/30);
/************************************************************ OUTPUT ********************************************/
   Serial.println(raw,DEC);
    
/************************************************************ OUTPUT ********************************************/

    //  PrintSignedNumber(derivative);
  }

#if 0
  /*ensure a sample rate of about 500Hz*/
  time = (micros()-time); //how much time has evolved since we started the read and
  if((Period500Hz-time)> 0){ 
    delayMicroseconds(Period500Hz-time); 
  }
  else{
    for(i = 0; i>10;i++){
      Serial.print("cannot run at 500Hz sampling rate");  
      delay(1000);  
    }  
  }
#endif

}




void PrintSignedNumber(unsigned long rawin){
  unsigned long bin_nofract;
  unsigned long fract;

  //otherwise its positive
  Serial.print(PSTR(" "));  
  bin_nofract = (rawin>>2)&0x03FFFF;
  fract = (rawin & 0x03)*0x19;


  Serial.print(bin_nofract, DEC);
  Serial.print(".");
  Serial.println(fract,DEC);

}


unsigned int SingleBarometerRead(unsigned long *raw){


  /*Temporary output data*/
  unsigned long MSB_Data = 0; 
  unsigned long CSB_Data = 0; 
  unsigned long LSB_Data = 0; 


  I2c.write(baro,CTRL_REG1,set_OST_OS); //initiates a single barometer read.  
  delay(0); /*The typical data rate in OST - one shot mode is 100Hz*/
  
  I2c.read(baro,OUT_P_MSB,8);
  MSB_Data = I2c.receive();//these are the 8 MSB out of the total of 20-bit

  I2c.read(baro,OUT_P_CSB,8);
  CSB_Data = I2c.receive();//these are the 8 CSB out of a total of 20-bits

  I2c.read(baro,OUT_P_LSB,8);
  LSB_Data = (I2c.receive());//these are the 4 LSB of the 20-bit output. 
  //The bitmap of the value received from the barometer however places these at the 4 MSB positions of the 8-bit word received. 
  //The lower 4-bits are '0'. THus we rightshift to get rid of these.
  //CHANGED: we ignore the fraction now...
   //Serial.println(((MSB_Data<<10)|(CSB_Data<<2)|LSB_Data>>6),DEC);


  *raw = (unsigned long)((MSB_Data<<10)|(CSB_Data<<2)|LSB_Data>>6);   //all output data put together. 
  if(raw != 0){
    return CP_OK;
  }
  else{
    return CP_ERROR;
  }

}