笔者最近想用气压计模块来测一下相对高度,使用的元器件如下图所示。
所使用的最小系统板 **
所使用的气压计模块
其实读取还是蛮简单的,根据核心板引脚图选择I2c接口,然后借鉴正点原子的模拟i2c程序,再根据datesheet里的图写出读气压计温度和大气压的程序,高度可由经验公式直接给出,笔者一开始对这个经验公式是持怀疑态度的,因为空气变化无常,咋可能根据这得出精确的高度,MS5611高度精度是10cm,已经很精确了。不过后来看来公式推导之后,发现还是很有道理了,自己想不通是自己菜,物理学家早就搞定了这些东西。
大气压与海拔高度公式推导
#include "MS5611.h"
#include "math.h"
#include "i2c.h"
#define SCTemperature 0x01
#define CTemperatureing 0x02
#define SCPressure 0x03
#define SCPressureing 0x04
uint32_t Cal_C[7];
double MSbaro_h;
double OFF_;
float Aux;
uint64_t dT,TEMP;
uint32_t yali,Pressure_old,qqp;
uint64_t OFf,SENS;
uint32_t D1_Pres,D2_Temp;
uint32_t TEMP2,T2,OFF2,SENS2;
uint32_t Pres_BUFFER[20];
uint32_t Temp_BUFFER[10];
void MS561101BA_RESET(void)
{
IIC_Start();
IIC_Send_Byte(0xEE);
IIC_Wait_Ack();
IIC_Send_Byte(0x1E);
IIC_Wait_Ack();
IIC_Stop();
}
u8 MS5611_init(void)
{
u8 inth,intl;
int i;
for (i=1;i<=6;i++)
{
IIC_Start();
IIC_Send_Byte(0xEE);
IIC_Wait_Ack();
IIC_Send_Byte(0xA0 + (i*2));
IIC_Wait_Ack();
IIC_Stop();
delay_us(5);
IIC_Start();
IIC_Send_Byte(0xEE+0x01);
delay_us(1);
IIC_Wait_Ack();
inth = IIC_Read_Byte(1);
delay_us(1);
intl = IIC_Read_Byte(0);
IIC_Stop();
Cal_C[i] = (((uint16_t)inth << 8) | intl);
}
return !Cal_C[0];
}
unsigned long MS561101BA_getConversion(uint8_t command)
{
unsigned long conversion = 0;
u8 temp[3];
IIC_Start();
IIC_Send_Byte(0xEE);
IIC_Wait_Ack();
IIC_Send_Byte(command);
IIC_Wait_Ack();
IIC_Stop();
delay_ms(10);
IIC_Start();
IIC_Send_Byte(0xEE);
IIC_Wait_Ack();
IIC_Send_Byte(0);
IIC_Wait_Ack();
IIC_Stop();
IIC_Start();
IIC_Send_Byte(0xEE+0x01);
IIC_Wait_Ack();
temp[0] = IIC_Read_Byte(1);
temp[1] = IIC_Read_Byte(1);
temp[2] = IIC_Read_Byte(0);
IIC_Stop();
conversion = (unsigned long)temp[0] * 65536 + (unsigned long)temp[1] * 256 + (unsigned long)temp[2];
return conversion;
}
void MS561101BA_GetTemperature(void)
{
D2_Temp = MS561101BA_getConversion(0x58);
delay_ms(10);
dT=D2_Temp - (((uint32_t)Cal_C[5])<<8);
TEMP=2000+dT*((uint32_t)Cal_C[6])/8388608;
}
void MS561101BA_getPressure(void)
{
D1_Pres= MS561101BA_getConversion(0x48);
delay_ms(10);
OFF_=(uint32_t)Cal_C[2]*65536+((uint32_t)Cal_C[4]*dT)/128;
SENS=(uint32_t)Cal_C[1]*32768+((uint32_t)Cal_C[3]*dT)/256;
if(TEMP<2000)
{
Aux = (2000-TEMP)*(2000-TEMP);
T2 = (dT*dT) / 0x80000000;
OFF2 = 2.5f*Aux;
SENS2 = 1.25f*Aux;
TEMP = TEMP - T2;
OFF_ = OFF_ - OFF2;
SENS = SENS - SENS2;
}
yali= (D1_Pres*SENS/2097152-OFF_)/32768;
MSbaro_h = 44330*(1-pow(((double)(yali))/((double)(101325)),1.0/5.255));
}
以上.c代码
```这个是.h代码c
#ifndef __MS5611_H_
#define __MS5611_H_
#include "stm32f10x.h"
#include "sys.h"
#include "delay.h"
#include "usart.h"
#include "i2c.h"
#define MS561101BA_ADC_RD 0x00
#define MS561101BA_PROM_RD 0xA0
#define MS561101BA_PROM_CRC 0xAE
#define MS561101BA_SlaveAddress 0xEE
#define MS561101BA_RST 0x1E
#define MS561101BA_D2_OSR_4096 0x58
#define MS561101BA_D1_OSR_4096 0x48
#define MS5611_OSR256 0x40
#define MS5611_OSR512 0x42
#define MS5611_OSR1024 0x44
#define MS5611_OSR2048 0x46
#define MS5611_OSR4096 0x48
#define FILTER_num 20
u8 MS5611_init(void);
float Get_High(void);
void Filter_Hight(unsigned int set_hight);
void Hight_PwmOut(void);
void MS561101BA_getPressure(void);
void MS561101BA_getTemperature(void);
void MS561101BA_RESET(void);
unsigned long MS561101BA_getConversion(uint8_t command);
void MS561101BA_GetTemperature(void);
extern uint64_t dT,TEMP;
extern uint32_t yali;
extern uint32_t Cal_C[7];
#endif
至于i2c直接借鉴正点原子的模拟i2c就可以了,不过要记得改下引脚
最后再说几句,对于我这种不是专业学电的,对于单片机这种的了解,基本上是在前人的基础上,改改引脚,再加上点C语言学习的大学,对于底层的一些通讯协议,只停留在了解的程度上,要是自己编的话,那真是好难啊!
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