Engineering 6maibarra: Lab 21 - BMP 180 Pressure and Altitude Sensor

CLASSWORK:

BMP 180 Pressure and Temperature Program:

// This is the top of the program

#include <Wire.h>

#include "BMP180Lib.c"

#define BMP180_ADDRESS 0x77 // I2C address of BMP180

//OSS = 0; // Oversampling Setting

short temperature;

long pressure;

// Use these for altitude conversions

const float p0 = 101325; // Pressure at sea level (Pa)

float altitude;

void setup()

{

Serial.begin(9600);

Wire.begin();

bmp180Calibration();

}

// Stores all of the bmp180's calibration values into global variables

// Calibration values are required to calculate temp and pressure

// This function should be called at the beginning of the program

void bmp180Calibration()

{

ac1 = bmp180ReadInt(0xAA);

ac2 = bmp180ReadInt(0xAC);

ac3 = bmp180ReadInt(0xAE);

ac4 = bmp180ReadInt(0xB0);

ac5 = bmp180ReadInt(0xB2);

ac6 = bmp180ReadInt(0xB4);

b1 = bmp180ReadInt(0xB6);

b2 = bmp180ReadInt(0xB8);

mb = bmp180ReadInt(0xBA);

mc = bmp180ReadInt(0xBC);

md = bmp180ReadInt(0xBE);

}

// Read 1 byte from the BMP180 at 'address'

char bmp180Read(unsigned char address)

{

unsigned char data;

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 1);

while(!Wire.available())

;

return Wire.read();

}

// Read 2 bytes from the BMP180

// First byte will be from 'address'

// Second byte will be from 'address'+1

int bmp180ReadInt(unsigned char address)

{

unsigned char msb, lsb;

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 2);

while(Wire.available()<2)

;

msb = Wire.read();

lsb = Wire.read();

return (int) msb<<8 | lsb;

}

// Read the uncompensated temperature value

unsigned int bmp180ReadUT()

{

unsigned int ut;

// Write 0x2E into Register 0xF4

// This requests a temperature reading

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF4);

Wire.write(0x2E);

Wire.endTransmission();

// Wait at least 4.5ms

delay(5);

// Read two bytes from registers 0xF6 and 0xF7

ut = bmp180ReadInt(0xF6);

return ut;

}

// Read the uncompensated pressure value

unsigned long bmp180ReadUP()

{

unsigned char msb, lsb, xlsb;

unsigned long up = 0;

// Write 0x34+(OSS<<6) into register 0xF4

// Request a pressure reading w/ oversampling setting

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF4);

Wire.write(0x34 + (OSS<<6));

Wire.endTransmission();

// Wait for conversion, delay time dependent on OSS

delay(2 + (3<<OSS));

// Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF6);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 3);

// Wait for data to become available

while(Wire.available() < 3)

;

msb = Wire.read();

lsb = Wire.read();

xlsb = Wire.read();

up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);

return up;

}

void loop()

{

temperature = bmp180GetTemperature(bmp180ReadUT());

pressure = bmp180GetPressure(bmp180ReadUP());

altitude = (float)44330 * (1 - pow(((float) pressure/p0), 0.190295));

Serial.print("Altitude: ");

Serial.print(altitude, 2);

Serial.println(" m");

Serial.print("Temperature: ");

Serial.print(temperature, DEC);

Serial.println(" *0.1 deg C");

Serial.print("Pressure: ");

Serial.print(pressure, DEC);

Serial.println(" Pa");

Serial.println();

delay(1000);

}

Header File: BMP180Lib.c

Note: This file should be included with the program above on a separate tab.

// Calibration values

int ac1;

int ac2;

int ac3;

unsigned int ac4;

unsigned int ac5;

unsigned int ac6;

int b1;

int b2;

int mb;

int mc;

int md;

// b5 is calculated in bmp180GetTemperature(...), this variable is also used in bmp180GetPressure(...)

// so ...Temperature(...) must be called before ...Pressure(...).

long b5;

// Calculate temperature given ut.

// Value returned will be in units of 0.1 deg C

const unsigned char OSS = 2; // Oversampling Setting

short bmp180GetTemperature(unsigned int ut)

{

long x1, x2;

x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;

x2 = ((long)mc << 11)/(x1 + md);

b5 = x1 + x2;

return ((b5 + 8)>>4);

}

// Calculate pressure given up

// calibration values must be known

// b5 is also required so bmp180GetTemperature(...) must be called first.

// Value returned will be pressure in units of Pa.

long bmp180GetPressure(unsigned long up)

{

long x1, x2, x3, b3, b6, p;

unsigned long b4, b7;

b6 = b5 - 4000;

// Calculate B3

x1 = (b2 * (b6 * b6)>>12)>>11;

x2 = (ac2 * b6)>>11;

x3 = x1 + x2;

b3 = (((((long)ac1)*4 + x3)<<OSS) + 2)>>2;

// Calculate B4

x1 = (ac3 * b6)>>13;

x2 = (b1 * ((b6 * b6)>>12))>>16;

x3 = ((x1 + x2) + 2)>>2;

b4 = (ac4 * (unsigned long)(x3 + 32768))>>15;

b7 = ((unsigned long)(up - b3) * (50000>>OSS));

if (b7 < 0x80000000)

p = (b7<<1)/b4;

else

p = (b7/b4)<<1;

x1 = (p>>8) * (p>>8);

x1 = (x1 * 3038)>>16;

x2 = (-7357 * p)>>16;

p += (x1 + x2 + 3791)>>4;

return p;

}

HOMEWORK:

Note: Could be optimized to write data at a higher rate:

//Reading Temperature, Pressure, and Altitude and writing to SD card

//Include the TimerOne library

#include <TimerOne.h>

#include <SD.h>

#include <Wire.h>

#include "BMP180Lib.c"

#define BMP180_ADDRESS 0x77 // I2C address of BMP180

//OSS = 0; // Oversampling Setting

short temperature;

long pressure;

//Set by default for the SD card library

const int CS_PIN = 10;

const int POW_PIN = 8;

// Use these for altitude conversions

const float p0 = 101325; // Pressure at sea level (Pa)

float altitude;

int count = 0;

long refresh_rate = 0; // in ms

//Volatile variables can change inside interrupts

volatile long timeStamp;

void setup()

{

//Set up Serial

Serial.begin(115200);

Wire.begin();

bmp180Calibration();

Serial.println("Initializing Card");

//CS pin is an output

pinMode(CS_PIN, OUTPUT);

pinMode(POW_PIN, OUTPUT);

digitalWrite(POW_PIN, HIGH);

if (!SD.begin(CS_PIN))

{

Serial.println("Card Failure");

return;

}

Serial.println("Card Ready");

//Read the configuration info (speed.txt)

File commandFile = SD.open("speed.txt");

if (commandFile)

{

Serial.println("Reading Command File");

while(commandFile.available())

{

refresh_rate = commandFile.parseInt();

}

Serial.print("Refresh Rate = ");

Serial.print(refresh_rate);

Serial.println(" ms");

commandFile.close(); //Close the file when finished

File dataFile = SD.open("sensor1.csv", FILE_WRITE);

dataFile.println("---------New Data Set--------");

dataFile.println("Time(s),Temp(C),Pressure(Pa),Altitude(m)");

dataFile.close();

Serial.println("--------New Data Set--------");

Serial.println("Time\t\tTempC\t\tPressure\tAltitude");

}

else

{

Serial.println("Could not read command file.");

return;

}

//Set up timer interrupt

Timer1.initialize(refresh_rate*1000); //Set a timer of length .02 seconds

Timer1.attachInterrupt(printData); //Runs "printData function" on each

//time interrupt

}

// Stores all of the bmp180's calibration values into global variables

// Calibration values are required to calculate temp and pressure

// This function should be called at the beginning of the program

void bmp180Calibration()

{

ac1 = bmp180ReadInt(0xAA);

ac2 = bmp180ReadInt(0xAC);

ac3 = bmp180ReadInt(0xAE);

ac4 = bmp180ReadInt(0xB0);

ac5 = bmp180ReadInt(0xB2);

ac6 = bmp180ReadInt(0xB4);

b1 = bmp180ReadInt(0xB6);

b2 = bmp180ReadInt(0xB8);

mb = bmp180ReadInt(0xBA);

mc = bmp180ReadInt(0xBC);

md = bmp180ReadInt(0xBE);

}

// Read 1 byte from the BMP180 at 'address'

char bmp180Read(unsigned char address)

{

unsigned char data;

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 1);

while(!Wire.available())

;

return Wire.read();

}

// Read 2 bytes from the BMP180

// First byte will be from 'address'

// Second byte will be from 'address'+1

int bmp180ReadInt(unsigned char address)

{

unsigned char msb, lsb;

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(address);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 2);

while(Wire.available()<2)

;

msb = Wire.read();

lsb = Wire.read();

return (int) msb<<8 | lsb;

}

// Read the uncompensated temperature value

unsigned int bmp180ReadUT()

{

unsigned int ut;

// Write 0x2E into Register 0xF4

// This requests a temperature reading

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF4);

Wire.write(0x2E);

Wire.endTransmission();

// Wait at least 4.5ms

delay(5);

// Read two bytes from registers 0xF6 and 0xF7

ut = bmp180ReadInt(0xF6);

return ut;

}

// Read the uncompensated pressure value

unsigned long bmp180ReadUP()

{

unsigned char msb, lsb, xlsb;

unsigned long up = 0;

// Write 0x34+(OSS<<6) into register 0xF4

// Request a pressure reading w/ oversampling setting

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF4);

Wire.write(0x34 + (OSS<<6));

Wire.endTransmission();

// Wait for conversion, delay time dependent on OSS

delay(2 + (3<<OSS));

// Read register 0xF6 (MSB), 0xF7 (LSB), and 0xF8 (XLSB)

Wire.beginTransmission(BMP180_ADDRESS);

Wire.write(0xF6);

Wire.endTransmission();

Wire.requestFrom(BMP180_ADDRESS, 3);

// Wait for data to become available

while(Wire.available() < 3)

;

msb = Wire.read();

lsb = Wire.read();

xlsb = Wire.read();

up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);

Engineering 6maibarra

Friday, December 15, 2017

Lab 21 - BMP 180 Pressure and Altitude Sensor

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