Kory Hill
/
BMP085_lib
demo program of BMP085 pressure sensor
Diff: main.cpp
- Revision:
- 0:9c929de0a051
- Child:
- 1:2935199329b2
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/main.cpp Fri Oct 05 08:03:52 2012 +0000 @@ -0,0 +1,208 @@ +/* +* +* +* +* 1.8 - 3.6V (Vdd) +* 1.62 - 3.6 (Vddio) +* +* +*Altitude = 44330*(1-(p/p0)^(1/5.255)) +* set p0 to sealevel pressure +* delta p = 1hPa = 8.43m at sea level +* +*/ + +/* +*Pinout: +*pin9 = SDA +*pin10 = SCL +*pin11 = XCLR (digital out; active low; Resets sensor) +*pin12 = EOC ("end of conversation"; signal when conversion finished) +* +* +* +*/ +#include "mbed.h" + +enum bmp085_oss {ULTRALOW, //samples 1 time + STANDARD, //samples twice + HIGH, //samples 4 times + ULTRAHIGH};//samples 8 times + + +I2C i2c(p9, p10); // sda, scl +Serial pc(USBTX, USBRX); // tx, rx + +const int bmp085_address = 0xEE; //address of bmp085 +const int P0 = 101325; //pressure at sea level + + +void bmp085_calibration(void); +void display_calibration(void); +unsigned short read_short(int,int); +void write_char(int,int,int); + +long get_raw_temp(void); +void calculations(long); +float get_altitude(long); + +short AC1, AC2, AC3, B1, B2, MB, MC, MD, OSS; +unsigned short AC4, AC5, AC6; + + + + + + +int main() { + + //Initialize + OSS = STANDARD; //change between enums under bmp085_oss for desired Sampling resolution + + //calibrate + bmp085_calibration(); + display_calibration(); + + long raw_temp = get_raw_temp(); + + calculations(raw_temp); + + //float altitude = get_altitude(pressure); + + //pc.printf("Temperature: %f\n",temperature); + //pc.printf("Pressure: %l\n", pressure); + //pc.printf("Altitude: %f\n", altitude); + + +} + +long get_raw_temp(void) +{ + long raw_temp; + + //Read raw temperature value + write_char(bmp085_address, 0xF4, 0x2E); + wait_ms(4.5); + raw_temp = read_short(bmp085_address, 0xF6); + + return raw_temp; +} + +void calculations(long raw_temp) +{ + long X1, X2, B5, temperature; + + //Start temperature calculation + X1 = (((long)raw_temp - (long)AC6) * (long)AC5) >> 15; + X2 = ((long)MC << 11) / (X1 + MD); + B5 = X1 + X2; + temperature = ((B5 + 8) >> 4); + + temperature = ((float)temperature / 10.0); + + pc.printf("Temperature: %f\n",temperature); + + + long raw_pressure, B6, B3, pressure, X3; + unsigned long B4, B7; + + //Read raw pressure value + write_char(bmp085_address, 0xf4, 0x34 | (OSS << 6)); + wait_ms(5); + raw_pressure = read_short(bmp085_address, 0xF6) >> (8 - OSS); + + //Start Pressure calculation + B6 = B5 - 4000; + X1 = (B2 * (B6 * B6) >> 12) >> 11; + X2 = (AC2 * B6) >> 11; + X3 = X1 + X2; + B3 = (((AC1 * 4 + X3) << OSS + 2) / 4); + 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)(raw_pressure - B3) * (50000 >> OSS)); + if (B7 < 0x80000000) + pressure = (B7 *2) / B4; + else + pressure = (B7 / B4) * 2; + + X1 = (pressure >> 8) * (pressure >>8); + X1 = (X1 * 3038) >>16; + X2 = (-7357 * pressure) >>16; + pressure += (X1 + X2 + 3791)>>4; + + pc.printf("Pressure: %f\n", pressure); + +} + +float get_altitude(long pressure) +{ + float altitude; + + altitude = (float)44330 * (1 - pow(( pressure/P0), 0.190295)); + + pc.printf("Altitude: %f\n", altitude); + return altitude; + +} + +void bmp085_calibration(void) +{ + AC1 = read_short(bmp085_address, 0xAA); + AC2 = read_short(bmp085_address, 0xAC); + AC3 = read_short(bmp085_address, 0xAE); + AC4 = read_short(bmp085_address, 0xB0); + AC5 = read_short(bmp085_address, 0xB2); + AC6 = read_short(bmp085_address, 0xB4); + B1 = read_short(bmp085_address, 0xB6); + B2 = read_short(bmp085_address, 0xB8); + MB = read_short(bmp085_address, 0xBA); + MC = read_short(bmp085_address, 0xBC); + MD = read_short(bmp085_address, 0xBE); + +} + +void display_calibration(void) +{ + pc.printf("Calibration Values:\n"); + pc.printf("AC1 = %d\n",AC1); + pc.printf("AC2 = %d\n",AC2); + pc.printf("AC3 = %d\n",AC3); + pc.printf("AC4 = %d\n",AC4); + pc.printf("AC5 = %d\n",AC5); + pc.printf("AC6 = %d\n",AC6); + pc.printf("B1 = %d\n",B1); + pc.printf("B2 = %d\n",B2); + pc.printf("MB = %d\n",MB); + pc.printf("MC = %d\n",MC); + pc.printf("MD = %d\n",MD); +} + +unsigned short read_short(int device_address,int address){ + unsigned short value; + + i2c.start(); + i2c.write(device_address); + i2c.write(address); + + i2c.start(); + i2c.write(device_address | 1); + value = i2c.read(1) << 8; + value |= i2c.read(0); + i2c.stop(); + + return value; + +} + +void write_char(int device_address, int address, int data) +{ + i2c.start(); + i2c.write(device_address); + i2c.write(address); + i2c.write(data); + i2c.stop(); +} + + \ No newline at end of file