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lib/SFE_BMP180/SFE_BMP180.cpp

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+/*
+	SFE_BMP180.cpp
+	Bosch BMP180 pressure sensor library for the Arduino microcontroller
+	Mike Grusin, SparkFun Electronics
+
+	Uses floating-point equations from the Weather Station Data Logger project
+	http://wmrx00.sourceforge.net/
+	http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
+
+	Forked from BMP085 library by M.Grusin
+
+	version 1.0 2013/09/20 initial version
+
+	Our example code uses the "beerware" license. You can do anything
+	you like with this code. No really, anything. If you find it useful,
+	buy me a (root) beer someday.
+*/
+
+#include <SFE_BMP180.h>
+#include <Wire.h>
+#include <stdio.h>
+#include <math.h>
+
+
+SFE_BMP180::SFE_BMP180()
+// Base library type
+{
+}
+
+
+char SFE_BMP180::begin()
+// Initialize library for subsequent pressure measurements
+{
+	double c3,c4,b1;
+	
+	// Start up the Arduino's "wire" (I2C) library:
+	
+	Wire.begin();
+
+	// The BMP180 includes factory calibration data stored on the device.
+	// Each device has different numbers, these must be retrieved and
+	// used in the calculations when taking pressure measurements.
+
+	// Retrieve calibration data from device:
+	
+	if (readInt(0xAA,AC1) &&
+		readInt(0xAC,AC2) &&
+		readInt(0xAE,AC3) &&
+		readUInt(0xB0,AC4) &&
+		readUInt(0xB2,AC5) &&
+		readUInt(0xB4,AC6) &&
+		readInt(0xB6,VB1) &&
+		readInt(0xB8,VB2) &&
+		readInt(0xBA,MB) &&
+		readInt(0xBC,MC) &&
+		readInt(0xBE,MD))
+	{
+
+		// All reads completed successfully!
+
+		// If you need to check your math using known numbers,
+		// you can uncomment one of these examples.
+		// (The correct results are commented in the below functions.)
+
+		// Example from Bosch datasheet
+		// AC1 = 408; AC2 = -72; AC3 = -14383; AC4 = 32741; AC5 = 32757; AC6 = 23153;
+		// B1 = 6190; B2 = 4; MB = -32768; MC = -8711; MD = 2868;
+
+		// Example from http://wmrx00.sourceforge.net/Arduino/BMP180-Calcs.pdf
+		// AC1 = 7911; AC2 = -934; AC3 = -14306; AC4 = 31567; AC5 = 25671; AC6 = 18974;
+		// VB1 = 5498; VB2 = 46; MB = -32768; MC = -11075; MD = 2432;
+
+		/*
+		Serial.print("AC1: "); Serial.println(AC1);
+		Serial.print("AC2: "); Serial.println(AC2);
+		Serial.print("AC3: "); Serial.println(AC3);
+		Serial.print("AC4: "); Serial.println(AC4);
+		Serial.print("AC5: "); Serial.println(AC5);
+		Serial.print("AC6: "); Serial.println(AC6);
+		Serial.print("VB1: "); Serial.println(VB1);
+		Serial.print("VB2: "); Serial.println(VB2);
+		Serial.print("MB: "); Serial.println(MB);
+		Serial.print("MC: "); Serial.println(MC);
+		Serial.print("MD: "); Serial.println(MD);
+		*/
+		
+		// Compute floating-point polynominals:
+
+		c3 = 160.0 * pow(2,-15) * AC3;
+		c4 = pow(10,-3) * pow(2,-15) * AC4;
+		b1 = pow(160,2) * pow(2,-30) * VB1;
+		c5 = (pow(2,-15) / 160) * AC5;
+		c6 = AC6;
+		mc = (pow(2,11) / pow(160,2)) * MC;
+		md = MD / 160.0;
+		x0 = AC1;
+		x1 = 160.0 * pow(2,-13) * AC2;
+		x2 = pow(160,2) * pow(2,-25) * VB2;
+		y0 = c4 * pow(2,15);
+		y1 = c4 * c3;
+		y2 = c4 * b1;
+		p0 = (3791.0 - 8.0) / 1600.0;
+		p1 = 1.0 - 7357.0 * pow(2,-20);
+		p2 = 3038.0 * 100.0 * pow(2,-36);
+
+		/*
+		Serial.println();
+		Serial.print("c3: "); Serial.println(c3);
+		Serial.print("c4: "); Serial.println(c4);
+		Serial.print("c5: "); Serial.println(c5);
+		Serial.print("c6: "); Serial.println(c6);
+		Serial.print("b1: "); Serial.println(b1);
+		Serial.print("mc: "); Serial.println(mc);
+		Serial.print("md: "); Serial.println(md);
+		Serial.print("x0: "); Serial.println(x0);
+		Serial.print("x1: "); Serial.println(x1);
+		Serial.print("x2: "); Serial.println(x2);
+		Serial.print("y0: "); Serial.println(y0);
+		Serial.print("y1: "); Serial.println(y1);
+		Serial.print("y2: "); Serial.println(y2);
+		Serial.print("p0: "); Serial.println(p0);
+		Serial.print("p1: "); Serial.println(p1);
+		Serial.print("p2: "); Serial.println(p2);
+		*/
+		
+		// Success!
+		return(1);
+	}
+	else
+	{
+		// Error reading calibration data; bad component or connection?
+		return(0);
+	}
+}
+
+
+char SFE_BMP180::readInt(char address, int &value)
+// Read a signed integer (two bytes) from device
+// address: register to start reading (plus subsequent register)
+// value: external variable to store data (function modifies value)
+{
+	unsigned char data[2];
+
+	data[0] = address;
+	if (readBytes(data,2))
+	{
+		value = (((int)data[0]<<8)|(int)data[1]);
+		//if (*value & 0x8000) *value |= 0xFFFF0000; // sign extend if negative
+		return(1);
+	}
+	value = 0;
+	return(0);
+}
+
+
+char SFE_BMP180::readUInt(char address, unsigned int &value)
+// Read an unsigned integer (two bytes) from device
+// address: register to start reading (plus subsequent register)
+// value: external variable to store data (function modifies value)
+{
+	unsigned char data[2];
+
+	data[0] = address;
+	if (readBytes(data,2))
+	{
+		value = (((unsigned int)data[0]<<8)|(unsigned int)data[1]);
+		return(1);
+	}
+	value = 0;
+	return(0);
+}
+
+
+char SFE_BMP180::readBytes(unsigned char *values, char length)
+// Read an array of bytes from device
+// values: external array to hold data. Put starting register in values[0].
+// length: number of bytes to read
+{
+	char x;
+
+	Wire.beginTransmission(BMP180_ADDR);
+	Wire.write(values[0]);
+	_error = Wire.endTransmission();
+	if (_error == 0)
+	{
+		Wire.requestFrom(BMP180_ADDR,length);
+		while(Wire.available() != length) ; // wait until bytes are ready
+		for(x=0;x<length;x++)
+		{
+			values[x] = Wire.read();
+		}
+		return(1);
+	}
+	return(0);
+}
+
+
+char SFE_BMP180::writeBytes(unsigned char *values, char length)
+// Write an array of bytes to device
+// values: external array of data to write. Put starting register in values[0].
+// length: number of bytes to write
+{
+	char x;
+	
+	Wire.beginTransmission(BMP180_ADDR);
+	Wire.write(values,length);
+	_error = Wire.endTransmission();
+	if (_error == 0)
+		return(1);
+	else
+		return(0);
+}
+
+
+char SFE_BMP180::startTemperature(void)
+// Begin a temperature reading.
+// Will return delay in ms to wait, or 0 if I2C error
+{
+	unsigned char data[2], result;
+	
+	data[0] = BMP180_REG_CONTROL;
+	data[1] = BMP180_COMMAND_TEMPERATURE;
+	result = writeBytes(data, 2);
+	if (result) // good write?
+		return(5); // return the delay in ms (rounded up) to wait before retrieving data
+	else
+		return(0); // or return 0 if there was a problem communicating with the BMP
+}
+
+
+char SFE_BMP180::getTemperature(double &T)
+// Retrieve a previously-started temperature reading.
+// Requires begin() to be called once prior to retrieve calibration parameters.
+// Requires startTemperature() to have been called prior and sufficient time elapsed.
+// T: external variable to hold result.
+// Returns 1 if successful, 0 if I2C error.
+{
+	unsigned char data[2];
+	char result;
+	double tu, a;
+	
+	data[0] = BMP180_REG_RESULT;
+
+	result = readBytes(data, 2);
+	if (result) // good read, calculate temperature
+	{
+		tu = (data[0] * 256.0) + data[1];
+
+		//example from Bosch datasheet
+		//tu = 27898;
+
+		//example from http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
+		//tu = 0x69EC;
+		
+		a = c5 * (tu - c6);
+		T = a + (mc / (a + md));
+
+		/*		
+		Serial.println();
+		Serial.print("tu: "); Serial.println(tu);
+		Serial.print("a: "); Serial.println(a);
+		Serial.print("T: "); Serial.println(*T);
+		*/
+	}
+	return(result);
+}
+
+
+char SFE_BMP180::startPressure(char oversampling)
+// Begin a pressure reading.
+// Oversampling: 0 to 3, higher numbers are slower, higher-res outputs.
+// Will return delay in ms to wait, or 0 if I2C error.
+{
+	unsigned char data[2], result, delay;
+	
+	data[0] = BMP180_REG_CONTROL;
+
+	switch (oversampling)
+	{
+		case 0:
+			data[1] = BMP180_COMMAND_PRESSURE0;
+			delay = 5;
+		break;
+		case 1:
+			data[1] = BMP180_COMMAND_PRESSURE1;
+			delay = 8;
+		break;
+		case 2:
+			data[1] = BMP180_COMMAND_PRESSURE2;
+			delay = 14;
+		break;
+		case 3:
+			data[1] = BMP180_COMMAND_PRESSURE3;
+			delay = 26;
+		break;
+		default:
+			data[1] = BMP180_COMMAND_PRESSURE0;
+			delay = 5;
+		break;
+	}
+	result = writeBytes(data, 2);
+	if (result) // good write?
+		return(delay); // return the delay in ms (rounded up) to wait before retrieving data
+	else
+		return(0); // or return 0 if there was a problem communicating with the BMP
+}
+
+
+char SFE_BMP180::getPressure(double &P, double &T)
+// Retrieve a previously started pressure reading, calculate abolute pressure in mbars.
+// Requires begin() to be called once prior to retrieve calibration parameters.
+// Requires startPressure() to have been called prior and sufficient time elapsed.
+// Requires recent temperature reading to accurately calculate pressure.
+
+// P: external variable to hold pressure.
+// T: previously-calculated temperature.
+// Returns 1 for success, 0 for I2C error.
+
+// Note that calculated pressure value is absolute mbars, to compensate for altitude call sealevel().
+{
+	unsigned char data[3];
+	char result;
+	double pu,s,x,y,z;
+	
+	data[0] = BMP180_REG_RESULT;
+
+	result = readBytes(data, 3);
+	if (result) // good read, calculate pressure
+	{
+		pu = (data[0] * 256.0) + data[1] + (data[2]/256.0);
+
+		//example from Bosch datasheet
+		//pu = 23843;
+
+		//example from http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf, pu = 0x982FC0;	
+		//pu = (0x98 * 256.0) + 0x2F + (0xC0/256.0);
+		
+		s = T - 25.0;
+		x = (x2 * pow(s,2)) + (x1 * s) + x0;
+		y = (y2 * pow(s,2)) + (y1 * s) + y0;
+		z = (pu - x) / y;
+		P = (p2 * pow(z,2)) + (p1 * z) + p0;
+
+		/*
+		Serial.println();
+		Serial.print("pu: "); Serial.println(pu);
+		Serial.print("T: "); Serial.println(*T);
+		Serial.print("s: "); Serial.println(s);
+		Serial.print("x: "); Serial.println(x);
+		Serial.print("y: "); Serial.println(y);
+		Serial.print("z: "); Serial.println(z);
+		Serial.print("P: "); Serial.println(*P);
+		*/
+	}
+	return(result);
+}
+
+
+double SFE_BMP180::sealevel(double P, double A)
+// Given a pressure P (mb) taken at a specific altitude (meters),
+// return the equivalent pressure (mb) at sea level.
+// This produces pressure readings that can be used for weather measurements.
+{
+	return(P/pow(1-(A/44330.0),5.255));
+}
+
+
+double SFE_BMP180::altitude(double P, double P0)
+// Given a pressure measurement P (mb) and the pressure at a baseline P0 (mb),
+// return altitude (meters) above baseline.
+{
+	return(44330.0*(1-pow(P/P0,1/5.255)));
+}
+
+
+char SFE_BMP180::getError(void)
+	// If any library command fails, you can retrieve an extended
+	// error code using this command. Errors are from the wire library: 
+	// 0 = Success
+	// 1 = Data too long to fit in transmit buffer
+	// 2 = Received NACK on transmit of address
+	// 3 = Received NACK on transmit of data
+	// 4 = Other error
+{
+	return(_error);
+}
+