/*
* bmp180.c:
* Extend wiringPi with the BMP180 I2C Pressure and Temperature
* sensor. This is used in the Pi Weather Station
* Copyright (c) 2016 Gordon Henderson
*
* Information from the document held at:
* http://wmrx00.sourceforge.net/Arduino/BMP085-Calcs.pdf
* was very useful when building this code.
*
***********************************************************************
* This file is part of wiringPi:
* https://projects.drogon.net/raspberry-pi/wiringpi/
*
* wiringPi is free software: you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* wiringPi is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with wiringPi.
* If not, see .
***********************************************************************
*/
#include
#include
#include
#include
#include "wiringPi.h"
#include "wiringPiI2C.h"
#include "bmp180.h"
#undef DEBUG
#define I2C_ADDRESS 0x77
#define BMP180_OSS 0
// Static calibration data
// The down-side of this is that there can only be one BMP180 in
// a system - which is practice isn't an issue as it's I2C
// address is fixed.
static int16_t AC1, AC2, AC3 ;
static uint16_t AC4, AC5, AC6 ;
static int16_t VB1, VB2 ;
static int16_t MB, MC, MD ;
static double c5, c6, mc, md, x0, x1, x2, yy0, yy1, yy2, p0, p1, p2 ;
// Pressure & Temp variables
uint32_t cPress, cTemp ;
static int altitude ;
/*
* read16:
* Quick hack to read the 16-bit data with the correct endian
*********************************************************************************
*/
uint16_t read16 (int fd, int reg)
{
return (wiringPiI2CReadReg8 (fd, reg) << 8) | wiringPiI2CReadReg8 (fd, reg + 1) ;
}
/*
* bmp180ReadTempPress:
* Does the hard work of reading the sensor
*********************************************************************************
*/
static void bmp180ReadTempPress (int fd)
{
double fTemp, fPress ;
double tu, a ;
double pu, s, x, y, z ;
uint8_t data [4] ;
// Start a temperature sensor reading
wiringPiI2CWriteReg8 (fd, 0xF4, 0x2E) ;
delay (5) ;
// Read the raw data
data [0] = wiringPiI2CReadReg8 (fd, 0xF6) ;
data [1] = wiringPiI2CReadReg8 (fd, 0xF7) ;
// And calculate...
tu = (data [0] * 256.0) + data [1] ;
a = c5 * (tu - c6) ;
fTemp = a + (mc / (a + md)) ;
cTemp = (int)rint (((100.0 * fTemp) + 0.5) / 10.0) ;
#ifdef DEBUG
printf ("fTemp: %f, cTemp: %6d\n", fTemp, cTemp) ;
#endif
// Start a pressure snsor reading
wiringPiI2CWriteReg8 (fd, 0xF4, 0x34 | (BMP180_OSS << 6)) ;
delay (5) ;
// Read the raw data
data [0] = wiringPiI2CReadReg8 (fd, 0xF6) ;
data [1] = wiringPiI2CReadReg8 (fd, 0xF7) ;
data [2] = wiringPiI2CReadReg8 (fd, 0xF8) ;
// And calculate...
pu = ((double)data [0] * 256.0) + (double)data [1] + ((double)data [2] / 256.0) ;
s = fTemp - 25.0 ;
x = (x2 * pow (s, 2.0)) + (x1 * s) + x0 ;
y = (yy2 * pow (s, 2.0)) + (yy1 * s) + yy0 ;
z = (pu - x) / y ;
fPress = (p2 * pow (z, 2.0)) + (p1 * z) + p0 ;
cPress = (int)rint (((100.0 * fPress) + 0.5) / 10.0) ;
#ifdef DEBUG
printf ("fPress: %f, cPress: %6d\n", fPress, cPress) ;
#endif
}
/*
* myAnalogWrite:
* Write to a fake register to represent the height above sea level
* so that the peudo millibar register can read the pressure in mB
*********************************************************************************
*/
static void myAnalogWrite (struct wiringPiNodeStruct *node, int pin, int value)
{
int chan = pin - node->pinBase ;
if (chan == 0)
altitude = value ;
}
/*
* myAnalogRead:
*********************************************************************************
*/
static int myAnalogRead (struct wiringPiNodeStruct *node, int pin)
{
int chan = pin - node->pinBase ;
bmp180ReadTempPress (node->fd) ;
/**/ if (chan == 0) // Read Temperature
return cTemp ;
else if (chan == 1) // Pressure
return cPress ;
else if (chan == 2) // Pressure in mB
return cPress / pow (1 - ((double)altitude / 44330.0), 5.255) ;
else
return -9999 ;
}
/*
* bmp180Setup:
* Create a new instance of a PCF8591 I2C GPIO interface. We know it
* has 4 pins, (4 analog inputs and 1 analog output which we'll shadow
* input 0) so all we need to know here is the I2C address and the
* user-defined pin base.
*********************************************************************************
*/
int bmp180Setup (const int pinBase)
{
double c3, c4, b1 ;
int fd ;
struct wiringPiNodeStruct *node ;
if ((fd = wiringPiI2CSetup (I2C_ADDRESS)) < 0)
return FALSE ;
node = wiringPiNewNode (pinBase, 4) ;
node->fd = fd ;
node->analogRead = myAnalogRead ;
node->analogWrite = myAnalogWrite ;
// Read calibration data
AC1 = read16 (fd, 0xAA) ;
AC2 = read16 (fd, 0xAC) ;
AC3 = read16 (fd, 0xAE) ;
AC4 = read16 (fd, 0xB0) ;
AC5 = read16 (fd, 0xB2) ;
AC6 = read16 (fd, 0xB4) ;
VB1 = read16 (fd, 0xB6) ;
VB2 = read16 (fd, 0xB8) ;
MB = read16 (fd, 0xBA) ;
MC = read16 (fd, 0xBC) ;
MD = read16 (fd, 0xBE) ;
// Calculate coefficients
c3 = 160.0 * pow (2.0, -15.0) * AC3 ;
c4 = pow (10.0, -3.0) * pow(2.0,-15.0) * AC4 ;
b1 = pow (160.0, 2.0) * pow(2.0,-30.0) * VB1 ;
c5 = (pow (2.0, -15.0) / 160.0) * AC5 ;
c6 = AC6 ;
mc = (pow (2.0, 11.0) / pow(160.0,2.0)) * MC ;
md = MD / 160.0 ;
x0 = AC1 ;
x1 = 160.0 * pow (2.0, -13.0) * AC2 ;
x2 = pow (160.0, 2.0) * pow(2.0,-25.0) * VB2 ;
yy0 = c4 * pow (2.0, 15.0) ;
yy1 = c4 * c3 ;
yy2 = c4 * b1 ;
p0 = (3791.0 - 8.0) / 1600.0 ;
p1 = 1.0 - 7357.0 * pow (2.0, -20.0) ;
p2 = 3038.0 * 100.0 * pow (2.0, -36.0) ;
return TRUE ;
}