Multiple BMP180 Sensors using I2C multiplexer

sandbee · November 27, 2017, 1:36pm

I am trying to get to Multiple BMP180 using I2C TCA9548A multiplexer connected to one Arduino Uno. Please see the code and library, wiring below. The following code printing "0" to the right when I'm using one BMp180. Am I missing something, Please let me know

Library MultiBMP085.h

#ifndef MultiBMP085_h
#define MultiBMP085_h

#include "Arduino.h"

class MultiBMP085 {
  public:
    MultiBMP085(int assignPin);
    boolean BMP085_begin();
    float getTemperature();
    short getPressure();
  private:
    int _pin;
    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;
    long b5; 
	const unsigned char OSS = 0;
    void Calibrate();
    unsigned int ReadUT();
    int ReadInt(unsigned char address);
    unsigned long ReadUP();
  
} ;


#endif

Library MultiBMP085.cpp

 #include "Arduino.h"
 #include "MultiBMP085.h"
 #include <Wire.h>

 #define BMP085_ADDRESS 0x77 //I2C address of BMP085
 

 MultiBMP085::MultiBMP085(int assignPin)  // Used when creating the class variables, assigned what pin the BMP085 XCLR is in
 {
    pinMode(assignPin, OUTPUT);
    _pin = assignPin; 
    digitalWrite(_pin, LOW);
 }
 
 boolean MultiBMP085 :: BMP085_begin(){
  digitalWrite(_pin, HIGH);
  delay(10);
  
  ac1 = ReadInt(0xAA);
  ac2 = ReadInt(0xAC);
  ac3 = ReadInt(0xAE);
  ac4 = ReadInt(0xB0);
  ac5 = ReadInt(0xB2);
  ac6 = ReadInt(0xB4);
  b1  = ReadInt(0xB6);
  b2  = ReadInt(0xB8);
  mb  = ReadInt(0xBA);
  mc  = ReadInt(0xBC);
  md  = ReadInt(0xBE);
  
  digitalWrite(_pin,LOW);
 }
 
 float MultiBMP085 :: getTemperature(){
    digitalWrite(_pin,HIGH);
    delay(5);
    unsigned int ut = ReadUT();
    long x1, x2;
  
    x1 = (((long)ut - (long)ac6)*(long)ac5) >> 15;
    x2 = ((long)mc << 11)/(x1 + md);
    b5 = x1 + x2;

    digitalWrite(_pin,LOW);
	delay(5);
	
	float toReturn = ((b5 +8)>>4)/10.0;
	
    return toReturn;  
   
 }

 short MultiBMP085:: getPressure(){
	 digitalWrite(_pin,HIGH);
    delay(5);
    short na = getTemperature(); //Need to make sure b5 is set before getting pressure
	unsigned long up = ReadUP(); 
    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));              //HERE
  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;
  
      digitalWrite(_pin,LOW);
  
  return p;
  
 }

 unsigned int MultiBMP085 :: ReadUT(){
  unsigned int ut;
  
  // Write 0x2E into Register 0xF4
  // This requests a temperature reading
  Wire.beginTransmission(BMP085_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 = ReadInt(0xF6);
  return ut;
 }

 int MultiBMP085 :: ReadInt(unsigned char address){
  unsigned char msb, lsb;
  
  Wire.beginTransmission(BMP085_ADDRESS);
  Wire.write(address);
  Wire.endTransmission();
  
  Wire.requestFrom(BMP085_ADDRESS, 2);
  while(Wire.available()<2){
  Serial.print(Wire.available());  
  delay(100); }
  ;
  msb = Wire.read();
  lsb = Wire.read();
  
  return (int) msb<<8 | lsb; 
 }

 unsigned long MultiBMP085 :: ReadUP(){
  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)
  Wire.beginTransmission(BMP085_ADDRESS);
  Wire.write(0xF6);
  Wire.endTransmission();
  Wire.requestFrom(BMP085_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;
 }

sandbee · November 27, 2017, 1:41pm

This is code which I'm testing

#include <Wire.h>

#define BMP085_ADDRESS 0x77  // I2C address of BMP085


int count=0;

const unsigned char OSS = 0;  // Oversampling Setting

// Calibration values
const int numBMP085=3;      //Number of BMP085 sensors being used, used to make array sizes
int BMPpin[numBMP085];

int ac1[numBMP085];
int ac2[numBMP085]; 
int ac3[numBMP085]; 
unsigned int ac4[numBMP085];
unsigned int ac5[numBMP085];
unsigned int ac6[numBMP085];
int b1[numBMP085]; 
int b2[numBMP085];
int mb[numBMP085];
int mc[numBMP085];
int md[numBMP085];

// b5 is calculated in bmp085GetTemperature(...), this variable is also used in bmp085GetPressure(...)
// so ...Temperature(...) must be called before ...Pressure(...).
long b5; 

short temperature;
long pressure;

void setup()
{
  Serial.begin(9600);
  Wire.begin();
    delay(1000);
   
for(int i=0;i<numBMP085;i++){

   BMPpin[i]=12-i;                    //Set a pin number for each sensor, first is 13, 2nd is 12, etc
   pinMode(BMPpin[i],OUTPUT);         //Use BMPpin[0] to HIGH to turn on sensor 1, attached to pin 13
   //Serial.println(BMPpin[i]);
}                                     
   
  for(int i=0;i<numBMP085;i++){
      
    Serial.print("Calibrate sensor #");
    Serial.println(i);
    
    useSensor(i);
    

    bmp085Calibration(i);                //Calibrate the sensor for pin i
  }    

    delay(500);



  
}

void loop()
{
  
if(count==numBMP085){
  count=0;
}

  int sensor=count;                      //The sensor being used will be determined by loop count,
                                         //reset to 0 at numBMP085
  useSensor(sensor);
  Serial.print("Sensor #");
  Serial.print(sensor);
  Serial.print(": ");
  
  
  delay(5);
  count++;
  
  temperature = bmp085GetTemperature(bmp085ReadUT(),sensor);
  pressure = bmp085GetPressure(bmp085ReadUP(),sensor);
  Serial.print("Temperature: ");
  Serial.print(temperature/10.,1);
  Serial.print(" deg C");
  Serial.print("\tPressure: ");
  Serial.print(pressure, DEC);
  Serial.println(" Pa");
//  Serial.println();
// delay(1000);
}

// 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(int sensorNum)
{
  ac1[sensorNum] = bmp085ReadInt(0xAA);
  ac2[sensorNum] = bmp085ReadInt(0xAC);
  ac3[sensorNum] = bmp085ReadInt(0xAE);
  ac4[sensorNum] = bmp085ReadInt(0xB0);
  ac5[sensorNum] = bmp085ReadInt(0xB2);
  ac6[sensorNum] = bmp085ReadInt(0xB4);
  b1[sensorNum] = bmp085ReadInt(0xB6);
  b2[sensorNum] = bmp085ReadInt(0xB8);
  mb[sensorNum] = bmp085ReadInt(0xBA);
  mc[sensorNum] = bmp085ReadInt(0xBC);
  md[sensorNum] = bmp085ReadInt(0xBE);
/*Serial.print("Sensor number ");
  Serial.println(sensorNum);
  Serial.println(ac1[sensorNum]);
  Serial.println(ac2[sensorNum]);
  Serial.println(ac3[sensorNum]);
  Serial.println(ac4[sensorNum]);
  Serial.println(ac5[sensorNum]);
  Serial.println(ac6[sensorNum]);
  Serial.println(b1[sensorNum]);
  Serial.println(b2[sensorNum]);
  Serial.println(mb[sensorNum]);
  Serial.println(mc[sensorNum]);
  Serial.println(md[sensorNum]);*/
}

// Calculate temperature given ut.
// Value returned will be in units of 0.1 deg C
short bmp085GetTemperature(unsigned int ut, int sensor)
{
  long x1, x2;
  
  x1 = (((long)ut - (long)ac6[sensor])*(long)ac5[sensor]) >> 15;
  x2 = ((long)mc[sensor] << 11)/(x1 + md[sensor]);
  b5 = x1 + x2;

  return ((b5 + 8)>>4);  
}

// 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,int sensor)
{
  long x1, x2, x3, b3, b6, p;
  unsigned long b4, b7;
  
  b6 = b5 - 4000;
  // Calculate B3
  x1 = (b2[sensor] * (b6 * b6)>>12)>>11;
  x2 = (ac2[sensor] * b6)>>11;
  x3 = x1 + x2;
  b3 = (((((long)ac1[sensor])*4 + x3)<<OSS) + 2)>>2;
  
  // Calculate B4
  x1 = (ac3[sensor] * b6)>>13;
  x2 = (b1[sensor] * ((b6 * b6)>>12))>>16;
  x3 = ((x1 + x2) + 2)>>2;
  b4 = (ac4[sensor] * (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;
}

// Read 1 byte from the BMP085 at 'address'
char bmp085Read(unsigned char address)
{
  unsigned char data;
  
  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(unsigned char address)
{
  unsigned char msb, lsb;
  
  Wire.beginTransmission(BMP085_ADDRESS);
  Wire.write(address);
  Wire.endTransmission();
  
  Wire.requestFrom(BMP085_ADDRESS, 2);
  while(Wire.available()<2){
  Serial.print(Wire.available());  
  delay(100); }
;
  msb = Wire.read();
  lsb = Wire.read();
  
  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(0xF4);
  Wire.write(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)
  Wire.beginTransmission(BMP085_ADDRESS);
  Wire.write(0xF6);
  Wire.endTransmission();
  Wire.requestFrom(BMP085_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 useSensor(int sensorNum)
{
  

for(int i=0;i<numBMP085;i++){            //Set all pins to low, turn off all sensors
      digitalWrite(BMPpin[i],LOW);
    }
    
digitalWrite(BMPpin[sensorNum],HIGH);    //Set the pin to be calibrated to high
  delay(1);                              //<-- DON'T REMOVE THIS
                                         //I don't know why, but without this the pressures are too high

}

pylon · November 27, 2017, 3:36pm

In this code you're not using the library at all.

The BMP085 has an XCLR pin to select the chip. The BMP180 doesn't have such a pin. How did you connect the pins 10-12 to the your BMP180?
I cannot find any code that uses the TCA9548A.

wvmarle · November 28, 2017, 3:39am

The BMP085 and BMP180 are supposed fully software/firmware compatible, as long as you don't try to use the XCLR pin that is. Without circuit diagram no way to tell.

Also indeed code doesn't even use the library posted above.

The idea seems correct. Use pins to power the sensors one by one (making sure you give them enough time to start up - see data sheet on how to first initialise the sensor, you'll have to do this over and over again).

sandbee · November 28, 2017, 4:25am

Thanks for the reply, This is wiring I followed as shown in this

I knew it's for BME280 but I didn't find anything BMP180. Any suggestions on the wiring will be helpful.

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