1/*
2 SFE_BMP180.cpp
3 Bosch BMP180 pressure sensor library for the Arduino microcontroller
4 Mike Grusin, SparkFun Electronics
5 Uses floating-point equations from the Weather Station Data Logger project
7 http://wmrx00.sourceforge.net/
8 http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
9 Forked from BMP085 library by M.Grusin
11 version 1.0 2013/09/20 initial version
13 Verison 1.1.2 - Updated for Arduino 1.6.4 5/2015
14 Our example code uses the "beerware" license. You can do anything
16 you like with this code. No really, anything. If you find it useful,
17 buy me a (root) beer someday.
18*/
19#include <SFE_BMP180.h>
21#include <Wire.h>
22#include <stdio.h>
23#include <math.h>
24SFE_BMP180::SFE_BMP180()
27// Base library type
28{
29}
30char SFE_BMP180::begin()
33// Initialize library for subsequent pressure measurements
34{
35 double c3,c4,b1;
36
37 // Start up the Arduino's "wire" (I2C) library:
38
39 Wire.begin();
40 // The BMP180 includes factory calibration data stored on the device.
42 // Each device has different numbers, these must be retrieved and
43 // used in the calculations when taking pressure measurements.
44 // Retrieve calibration data from device:
46
47 if (readInt(0xAA,AC1) &&
48 readInt(0xAC,AC2) &&
49 readInt(0xAE,AC3) &&
50 readUInt(0xB0,AC4) &&
51 readUInt(0xB2,AC5) &&
52 readUInt(0xB4,AC6) &&
53 readInt(0xB6,VB1) &&
54 readInt(0xB8,VB2) &&
55 readInt(0xBA,MB) &&
56 readInt(0xBC,MC) &&
57 readInt(0xBE,MD))
58 {
59 // All reads completed successfully!
61 // If you need to check your math using known numbers,
63 // you can uncomment one of these examples.
64 // (The correct results are commented in the below functions.)
65 // Example from Bosch datasheet
67 // AC1 = 408; AC2 = -72; AC3 = -14383; AC4 = 32741; AC5 = 32757; AC6 = 23153;
68 // B1 = 6190; B2 = 4; MB = -32768; MC = -8711; MD = 2868;
69 // Example from http://wmrx00.sourceforge.net/Arduino/BMP180-Calcs.pdf
71 // AC1 = 7911; AC2 = -934; AC3 = -14306; AC4 = 31567; AC5 = 25671; AC6 = 18974;
72 // VB1 = 5498; VB2 = 46; MB = -32768; MC = -11075; MD = 2432;
73 /*
75 Serial.print("AC1: "); Serial.println(AC1);
76 Serial.print("AC2: "); Serial.println(AC2);
77 Serial.print("AC3: "); Serial.println(AC3);
78 Serial.print("AC4: "); Serial.println(AC4);
79 Serial.print("AC5: "); Serial.println(AC5);
80 Serial.print("AC6: "); Serial.println(AC6);
81 Serial.print("VB1: "); Serial.println(VB1);
82 Serial.print("VB2: "); Serial.println(VB2);
83 Serial.print("MB: "); Serial.println(MB);
84 Serial.print("MC: "); Serial.println(MC);
85 Serial.print("MD: "); Serial.println(MD);
86 */
87
88 // Compute floating-point polynominals:
89 c3 = 160.0 * pow(2,-15) * AC3;
91 c4 = pow(10,-3) * pow(2,-15) * AC4;
92 b1 = pow(160,2) * pow(2,-30) * VB1;
93 c5 = (pow(2,-15) / 160) * AC5;
94 c6 = AC6;
95 mc = (pow(2,11) / pow(160,2)) * MC;
96 md = MD / 160.0;
97 x0 = AC1;
98 x1 = 160.0 * pow(2,-13) * AC2;
99 x2 = pow(160,2) * pow(2,-25) * VB2;
100 y0 = c4 * pow(2,15);
101 y1 = c4 * c3;
102 y2 = c4 * b1;
103 p0 = (3791.0 - 8.0) / 1600.0;
104 p1 = 1.0 - 7357.0 * pow(2,-20);
105 p2 = 3038.0 * 100.0 * pow(2,-36);
106 /*
108 Serial.println();
109 Serial.print("c3: "); Serial.println(c3);
110 Serial.print("c4: "); Serial.println(c4);
111 Serial.print("c5: "); Serial.println(c5);
112 Serial.print("c6: "); Serial.println(c6);
113 Serial.print("b1: "); Serial.println(b1);
114 Serial.print("mc: "); Serial.println(mc);
115 Serial.print("md: "); Serial.println(md);
116 Serial.print("x0: "); Serial.println(x0);
117 Serial.print("x1: "); Serial.println(x1);
118 Serial.print("x2: "); Serial.println(x2);
119 Serial.print("y0: "); Serial.println(y0);
120 Serial.print("y1: "); Serial.println(y1);
121 Serial.print("y2: "); Serial.println(y2);
122 Serial.print("p0: "); Serial.println(p0);
123 Serial.print("p1: "); Serial.println(p1);
124 Serial.print("p2: "); Serial.println(p2);
125 */
126
127 // Success!
128 return(1);
129 }
130 else
131 {
132 // Error reading calibration data; bad component or connection?
133 return(1);
134 }
135}
136char SFE_BMP180::readInt(char address, int16_t &value)
139// Read a signed integer (two bytes) from device
140// address: register to start reading (plus subsequent register)
141// value: external variable to store data (function modifies value)
142{
143 unsigned char data[2];
144 data[0] = address;
146 if (readBytes(data,2))
147 {
148 value = (int16_t)((data[0]<<8)|data[1]);
149 //if (*value & 0x8000) *value |= 0xFFFF0000; // sign extend if negative
150 return(1);
151 }
152 value = 0;
153 return(0);
154}
155char SFE_BMP180::readUInt(char address, uint16_t &value)
158// Read an unsigned integer (two bytes) from device
159// address: register to start reading (plus subsequent register)
160// value: external variable to store data (function modifies value)
161{
162 unsigned char data[2];
163 data[0] = address;
165 if (readBytes(data,2))
166 {
167 value = (((uint16_t)data[0]<<8)|(uint16_t)data[1]);
168 return(1);
169 }
170 value = 0;
171 return(0);
172}
173char SFE_BMP180::readBytes(unsigned char *values, char length)
176// Read an array of bytes from device
177// values: external array to hold data. Put starting register in values[0].
178// length: number of bytes to read
179{
180 char x;
181 Wire.beginTransmission(BMP180_ADDR);
183 Wire.write(values[0]);
184 _error = Wire.endTransmission();
185 if (_error == 0)
186 {
187 Wire.requestFrom(BMP180_ADDR,length);
188 while(Wire.available() != length) ; // wait until bytes are ready
189 for(x=0;x<length;x++)
190 {
191 values[x] = Wire.read();
192 }
193 return(1);
194 }
195 return(0);
196}
197char SFE_BMP180::writeBytes(unsigned char *values, char length)
200// Write an array of bytes to device
201// values: external array of data to write. Put starting register in values[0].
202// length: number of bytes to write
203{
204 char x;
205
206 Wire.beginTransmission(BMP180_ADDR);
207 Wire.write(values,length);
208 _error = Wire.endTransmission();
209 if (_error == 0)
210 return(1);
211 else
212 return(0);
213}
214char SFE_BMP180::startTemperature(void)
217// Begin a temperature reading.
218// Will return delay in ms to wait, or 0 if I2C error
219{
220 unsigned char data[2], result;
221
222 data[0] = BMP180_REG_CONTROL;
223 data[1] = BMP180_COMMAND_TEMPERATURE;
224 result = writeBytes(data, 2);
225 if (result) // good write?
226 return(5); // return the delay in ms (rounded up) to wait before retrieving data
227 else
228 return(0); // or return 0 if there was a problem communicating with the BMP
229}
230char SFE_BMP180::getTemperature(double &T)
233// Retrieve a previously-started temperature reading.
234// Requires begin() to be called once prior to retrieve calibration parameters.
235// Requires startTemperature() to have been called prior and sufficient time elapsed.
236// T: external variable to hold result.
237// Returns 1 if successful, 0 if I2C error.
238{
239 unsigned char data[2];
240 char result;
241 double tu, a;
242
243 data[0] = BMP180_REG_RESULT;
244 result = readBytes(data, 2);
246 if (result) // good read, calculate temperature
247 {
248 tu = (data[0] * 256.0) + data[1];
249 //example from Bosch datasheet
251 //tu = 27898;
252 //example from http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
254 //tu = 0x69EC;
255
256 a = c5 * (tu - c6);
257 T = a + (mc / (a + md));
258 /*
260 Serial.println();
261 Serial.print("tu: "); Serial.println(tu);
262 Serial.print("a: "); Serial.println(a);
263 Serial.print("T: "); Serial.println(*T);
264 */
265 }
266 return(result);
267}
268char SFE_BMP180::startPressure(char oversampling)
271// Begin a pressure reading.
272// Oversampling: 0 to 3, higher numbers are slower, higher-res outputs.
273// Will return delay in ms to wait, or 0 if I2C error.
274{
275 unsigned char data[2], result, delay;
276
277 data[0] = BMP180_REG_CONTROL;
278 switch (oversampling)
280 {
281 case 0:
282 data[1] = BMP180_COMMAND_PRESSURE0;
283 delay = 5;
284 break;
285 case 1:
286 data[1] = BMP180_COMMAND_PRESSURE1;
287 delay = 8;
288 break;
289 case 2:
290 data[1] = BMP180_COMMAND_PRESSURE2;
291 delay = 14;
292 break;
293 case 3:
294 data[1] = BMP180_COMMAND_PRESSURE3;
295 delay = 26;
296 break;
297 default:
298 data[1] = BMP180_COMMAND_PRESSURE0;
299 delay = 5;
300 break;
301 }
302 result = writeBytes(data, 2);
303 if (result) // good write?
304 return(delay); // return the delay in ms (rounded up) to wait before retrieving data
305 else
306 return(0); // or return 0 if there was a problem communicating with the BMP
307}
308char SFE_BMP180::getPressure(double &P, double &T)
311// Retrieve a previously started pressure reading, calculate abolute pressure in mbars.
312// Requires begin() to be called once prior to retrieve calibration parameters.
313// Requires startPressure() to have been called prior and sufficient time elapsed.
314// Requires recent temperature reading to accurately calculate pressure.
315// P: external variable to hold pressure.
317// T: previously-calculated temperature.
318// Returns 1 for success, 0 for I2C error.
319// Note that calculated pressure value is absolute mbars, to compensate for altitude call sealevel().
321{
322 unsigned char data[3];
323 char result;
324 double pu,s,x,y,z;
325
326 data[0] = BMP180_REG_RESULT;
327 result = readBytes(data, 3);
329 if (result) // good read, calculate pressure
330 {
331 pu = (data[0] * 256.0) + data[1] + (data[2]/256.0);
332 //example from Bosch datasheet
334 //pu = 23843;
335 //example from http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf, pu = 0x982FC0;
337 //pu = (0x98 * 256.0) + 0x2F + (0xC0/256.0);
338
339 s = T - 25.0;
340 x = (x2 * pow(s,2)) + (x1 * s) + x0;
341 y = (y2 * pow(s,2)) + (y1 * s) + y0;
342 z = (pu - x) / y;
343 P = (p2 * pow(z,2)) + (p1 * z) + p0;
344 /*
346 Serial.println();
347 Serial.print("pu: "); Serial.println(pu);
348 Serial.print("T: "); Serial.println(*T);
349 Serial.print("s: "); Serial.println(s);
350 Serial.print("x: "); Serial.println(x);
351 Serial.print("y: "); Serial.println(y);
352 Serial.print("z: "); Serial.println(z);
353 Serial.print("P: "); Serial.println(*P);
354 */
355 }
356 return(result);
357}
358double SFE_BMP180::sealevel(double P, double A)
361// Given a pressure P (mb) taken at a specific altitude (meters),
362// return the equivalent pressure (mb) at sea level.
363// This produces pressure readings that can be used for weather measurements.
364{
365 return(P/pow(1-(A/44330.0),5.255));
366}
367double SFE_BMP180::altitude(double P, double P0)
370// Given a pressure measurement P (mb) and the pressure at a baseline P0 (mb),
371// return altitude (meters) above baseline.
372{
373 return(44330.0*(1-pow(P/P0,1/5.255)));
374}
375char SFE_BMP180::getError(void)
378 // If any library command fails, you can retrieve an extended
379 // error code using this command. Errors are from the wire library:
380 // 0 = Success
381 // 1 = Data too long to fit in transmit buffer
382 // 2 = Received NACK on transmit of address
383 // 3 = Received NACK on transmit of data
384 // 4 = Other error
385{
386 return(_error);
387}
388