Hello,
I think I have a problem with my code. I am trying to take temperature and pressure readings from a BMP085 Bosch pressure sensor and an Arduino Nano and then trying to display the results in a 16x2 LCD screen with an LCD Interface. All my hardware is wired properly and I am getting readings to the LCD. The problem is my temperature is measuring properly and my pressure is not measuring properly. I’m getting 30,900 Pa instead of 101,325 Pa. I don’t know if I need to re-calibrate or reset the original settings? Maybe my code is wrong? Someone please help me! I have a big competition at my school tomorrow and I am trying to get this measuring tonight.
Here is my code:
#include <Wire.h>
#include <LiquidCrystal.h>
#define BMP085_ADDRESS 0x77 // I2C address of BMP085
#define MPTH 0x40 >> 1
const unsigned char OSS = 2; // Oversampling Setting
// 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 bmp085GetTemperature(…), this variable is also used in bmp085GetPressure(…)
// so …Temperature(…) must be called before …Pressure(…).
long b5;
void setup(){
Serial.begin(9600);
Wire.begin();
bmp085Calibration();
}
void loop()
{
float temperature = bmp085GetTemperature(bmp085ReadUT()); //MUST be called first
float pressure = bmp085GetPressure(bmp085ReadUP());
float atm = pressure / 101325; // “standard atmosphere”
float altitude = calcAltitude(pressure); //Uncompensated caculation - in Meters
clearText();
putText("Temp: ");
char tempString[8];
itoa((int) temperature, tempString, 10);
putText(tempString);
putText(" C");
delay(1000);
clearText();
putText("P.: ");
itoa((int) pressure, tempString, 10);
putText(tempString);
putText(" Pa");
/*
clearText();
putText("Temp: ");
char tempString[8];
itoa((int) temperature, tempString, 10);
putText(tempString);
putText(" C");
gotoLine2();
putText("P.: ");
itoa((int) pressure, tempString, 10);
putText(tempString);
putText(" Pa");
*/
delay(1000); //wait a second and get values again.
}
// Stores all of the bmp085’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 bmp085Calibration()
{
Serial.write("\n\nCalibrating … ");
ac1 = bmp085ReadInt(0xAA);
ac2 = bmp085ReadInt(0xAC);
ac3 = bmp085ReadInt(0xAE);
ac4 = bmp085ReadInt(0xB0);
ac5 = bmp085ReadInt(0xB2);
ac6 = bmp085ReadInt(0xB4);
b1 = bmp085ReadInt(0xB6);
b2 = bmp085ReadInt(0xB8);
mb = bmp085ReadInt(0xBA);
mc = bmp085ReadInt(0xBC);
md = bmp085ReadInt(0xBE);
Serial.write(“Calibrated\n\n”);
}
// Calculate temperature in deg C
float bmp085GetTemperature(unsigned int ut){
long x1, x2;
x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
x2 = ((long)mc << 11)/(x1 + md);
b5 = x1 + x2;
float temp = ((b5 + 8)>>4);
temp = temp /10;
return temp;
}
// Calculate pressure given up
// calibration values must be known
// b5 is also required so bmp085GetTemperature(…) must be called first.
// Value returned will be pressure in units of Pa.
long bmp085GetPressure(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;
long temp = p;
return temp;
}
// Read 1 byte from the BMP085 at ‘address’
char bmp085Read(byte address)
{
Wire.beginTransmission(BMP085_ADDRESS);
Wire.write(address);
Wire.endTransmission();
Wire.requestFrom(BMP085_ADDRESS, 1);
while(!Wire.available()) {
};
return Wire.read();
}
// Read 2 bytes from the BMP085
// First byte will be from ‘address’
// Second byte will be from ‘address’+1
int bmp085ReadInt(byte address)
{
Serial.println(“Started bmpReadInt()”);
unsigned char msb, lsb;
Serial.println(“\tBeginning transmission”);
Wire.beginTransmission(BMP085_ADDRESS);
Serial.println(“\tWriting…”);
Wire.write(address);
Serial.println(“\tWrote”);
Wire.endTransmission();
Serial.println(“\tFinished transmission. Requesting…”);
Wire.requestFrom(BMP085_ADDRESS, 2);
Serial.println(“\tRequested”);
while(Wire.available()<2)
;
Serial.println(“\tReady”);
msb = Wire.read();
lsb = Wire.read();
Serial.println(“Finished”);
return (int) msb<<8 | lsb;
}
// Read the uncompensated temperature value
unsigned int bmp085ReadUT(){
unsigned int ut;
// Write 0x2E into Register 0xF4
// This requests a temperature reading
Wire.beginTransmission(BMP085_ADDRESS);
Wire.write((byte)0xF4);
Wire.write((byte)0x2E);
Wire.endTransmission();
// Wait at least 4.5ms
delay(5);
// Read two bytes from registers 0xF6 and 0xF7
ut = bmp085ReadInt(0xF6);
return ut;
}
// Read the uncompensated pressure value
unsigned long bmp085ReadUP(){
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(BMP085_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)
msb = bmp085Read(0xF6);
lsb = bmp085Read(0xF7);
xlsb = bmp085Read(0xF8);
up = (((unsigned long) msb << 16) | ((unsigned long) lsb << 8) | (unsigned long) xlsb) >> (8-OSS);
return up;
}
void writeRegister(int deviceAddress, byte address, byte val) {
Wire.beginTransmission(deviceAddress); // start transmission to device
Wire.write(address); // send register address
Wire.write(val); // send value to write
Wire.endTransmission(); // end transmission
}
int readRegister(int deviceAddress, byte address){
int v;
Wire.beginTransmission(deviceAddress);
Wire.write(address); // register to read
Wire.endTransmission();
Wire.requestFrom(deviceAddress, 1); // read a byte
while(!Wire.available()) {
// waiting
}
v = Wire.read();
return v;
}
float calcAltitude(float pressure){
float A = pressure/101325;
float B = 1/5.25588;
float C = pow(A,B);
C = 1 - C;
C = C /0.0000225577;
return C;
}
void putText(char* txt) {
for (int i = 0; txt != ‘\0’; i++) {
I2C_TX(MPTH,txt);
}
}
void gotoLine2()
{
MPTHCOMMANDI2C(128,8,16);
}
void clearText()
{
MPTHCOMMANDI2C(128,5,1);
}
void I2C_TX(byte device, byte tx_data) // Transmit I2C Data (Use to send characters to the MPTH)
{
Wire.beginTransmission(device); // Send Slave (device) address
Wire.write(tx_data); // Send the data
Wire.endTransmission();
}
void MPTHCOMMANDI2C(byte MPSTART, byte MPCOM, byte MPSETTING) // Use to send commands to the MPTH
{
byte MPsend[3] = {
0,0,0 };
MPsend[0] = MPSTART;
MPsend[1] = MPCOM;
MPsend[2] = MPSETTING;
Wire.beginTransmission(MPTH); // Send Slave (device) address
Wire.write(MPsend, 3); // Send 3 bytes of data (Start - Command - value)
Wire.endTransmission();
}