sht.c

数字式温湿度传感器的控制源程序

/****************************************************************
 *文件名：sht.c
 *描述：提供数字式温湿度传感器的低层驱动程序
 *环境：KEIL C51
 *版本：v1.0
 *作者：wentsing
 *日期：2006/03/07
******************************************************************/

#include "include.h"

#define STH_C		1
#define CRC8		1								//需要CRC8计算

/****************************************************************
 *函数性质：SHT专用
 *入口：要写入的SHT的数据unsigned char value
 *出口：无
 *功能：writes a byte on the Sensibus and checks the acknowledge 
 *调用方式：uchar ShtWriteByte(unsigned char value)
*****************************************************************/
uchar ShtWriteByte(unsigned char value)
{ 
 	unsigned char i,error = 0;  
	for (i = 0x80; i > 0; i >>= 1)					//shift bit for masking
	{
		if (i & value)
			DATA = 1;								//masking value with i , write to SENSI-BUS
		else DATA = 0;                        
		SCK = 1;									//clk for SENSI-BUS
		NOP();NOP();NOP();							//pulswith approx. 5 us  	
		SCK = 0;
	}
	DATA = 1;										//release DATA-line
	SCK = 1;										//clk #9 for ack 
	error = DATA;									//check ack (DATA will be pulled down by SHT11)
	SCK = 0;        
	return error;									//error=1 in case of no acknowledge
}

/****************************************************************
 *函数性质：SHT专用
 *入口：要响应SHT的数据unsigned char ack
 *出口：返回读取的值
 *功能：reads a byte form the Sensibus and gives an acknowledge in case of "ack=1" 
 *调用方式：uchar ShtReadByte(unsigned char ack
*****************************************************************/
uchar ShtReadByte(unsigned char ack)
{ 
	unsigned char i,val = 0;
	DATA = 1;										//release DATA-line
	for ( i = 0x80; i > 0; i >>= 1)					//shift bit for masking
	{
		SCK = 1;									//clk for SENSI-BUS
		if (DATA)
			val | =  i;								//read bit  
		SCK = 0;  					 
	}
	DATA =! ack;									//in case of "ack==1" pull down DATA-Line
	SCK = 1;										//clk #9 for ack
	NOP();NOP();NOP();								//pulswith approx. 5 us 
	SCK = 0;						    
	DATA = 1;										//release DATA-line
	return val;
}

/****************************************************************
 *函数性质：SHT专用
 *入口：无
 *出口：无
 *功能：generates a transmission start for SHT
 *调用方式：void ShtTransStart(void)
*****************************************************************/
void ShtTransStart(void)
//---------------------------------------------------------------
//       _____         ________
// DATA:      |_______|
//           ___     ___
// SCK : ___|   |___|   |______
//---------------------------------------------------------------
{  
	DATA = 1;	SCK = 0;							//Initial state
	NOP();
	SCK = 1;
	NOP();
	DATA = 0;
	NOP();
	SCK = 0;  
	NOP();NOP();NOP();
	SCK = 1;
	NOP();
	DATA = 1;		   
	NOP();
	SCK = 0;		   
}

/****************************************************************
 *函数性质：专用
 *入口：无
 *出口：无
 *功能：communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
 *调用方式：ShtConnectRst(void)
*****************************************************************/
void ShtConnectRst(void)
//---------------------------------------------------------------
//       _____________________________________________________         ________
// DATA:                                                      |_______|
//          _    _    _    _    _    _    _    _    _        ___     ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______|   |___|   |______
//---------------------------------------------------------------
{  
	unsigned char i; 
	DATA = 1;	SCK = 0;							//Initial state
	for(i = 0; i < 9; i++)							//9 SCK cycles
	{
		SCK=1;
 		SCK=0;
	}
 	ShtTransStart();								//transmission start
}

/****************************************************************
 *函数性质：公共
 *入口：无
 *出口：返回成功或者失败
 *功能：resets the sensor by a softreset
 *调用方式：uchar ShtSoftReset(void)
*****************************************************************/
uchar ShtSoftReset(void)
{ 
	unsigned char error = 0;  
	ShtConnectRst();								//reset communication
	error += ShtWriteByte(RESET);					//send RESET-command to sensor
	return error;									//error=1 in case of no response form the sensor
}

/****************************************************************
 *函数性质：公共
 *入口：读入数据缓冲 unsigned char *p_value
 *出口：返回成功或者失败
 *功能：reads the status register with checksum (8-bit)
 *调用方式：uchar ShtReadStatusReg(unsigned char *p_value)
*****************************************************************/
uchar ShtReadStatusReg(unsigned char *p_value)
{ 
	unsigned char error = 0,crc;
 	ShtTransStart();								//transmission start
	error = ShtWriteByte(STATUS_REG_R);				//send command to sensor
	*p_value = ShtReadByte(1);					//read status register (8-bit)
	crc = ShtReadByte(0);						//read checksum (8-bit)  
	if(crc != CalCRC8(p_value, 1))
		error++;
	return error;									//error=1 in case of no response form the sensor or crc check error
}

/****************************************************************
 *函数性质：公共
 *入口：要写入的状态寄存器数据 unsigned char p_value
 *出口：返回成功或者失败
 *功能：writes the status register with checksum (8-bit)
 *调用方式：uchar ShtWriteStatusReg(unsigned char p_value)
*****************************************************************/
uchar ShtWriteStatusReg(unsigned char p_value)
{ 
	unsigned char error = 0;
	ShtTransStart();								//transmission start
	error += ShtWriteByte(STATUS_REG_W);			//send command to sensor
	error += ShtWriteByte(p_value);					//send value of status register
	return error;									//error>=1 in case of no response form the sensor
}

/****************************************************************
 *函数性质：公共
 *入口：返回值数据缓冲 unsigned char *p_value 测量类型unsigned char mode
 *出口：返回成功或者失败
 *功能：makes a measurement (humidity/temperature) with checksum
 *调用方式：unsigned char ShtMeasure(unsigned char *p_value,  unsigned char mode)
*****************************************************************/
unsigned char ShtMeasure(unsigned char *p_value,  unsigned char mode)
{ 
	unsigned char error = 0,crc;
	unsigned int i;

	ShtTransStart();								//transmission start
	switch(mode)
	{												//send command to sensor
		case TEMP	: 
			error += ShtWriteByte(MEASURE_TEMP); 
			break;
		case HUMI	: 
			error += ShtWriteByte(MEASURE_HUMI); 
			break;
		default     : 
			break;	 
	}
	for (i = 0; i < 65535; i++) 
		if(DATA == 0) 
			break;									//wait until sensor has finished the measurement
	if(DATA) 
		error ++;									// or timeout (~2 sec.) is reached
 	*p_value++  = ShtReadByte(1);					//read the first byte (MSB)
	*p_value = ShtReadByte(1);					//read the second byte (LSB)
	crc = ShtReadByte(0);						//read checksum
	if(crc != CalCRC8(p_value, 2))
		error++;
	return error;
}

/****************************************************************
 *函数性质：公共
 *入口：返回值湿度缓冲float *p_humidity ，返回值温度缓冲float *p_temperature
 *出口：无
 *功能：// calculates temperature [癈] and humidity [%RH] 
 *调用方式：void calc_sth11(float *p_humidity ,float *p_temperature)
*****************************************************************/
void calc_sth11(float *p_humidity ,float *p_temperature)
{
	const float C1 = -4.0;							// for 12 Bit
	const float C2 =+ 0.0405;						// for 12 Bit
	const float C3 =- 0.0000028;					// for 12 Bit
	const float T1 =+ 0.01;							// for 14 Bit @ 5V
	const float T2 =+ 0.00008;						// for 14 Bit @ 5V	

	float rh = *p_humidity;							// rh:      Humidity [Ticks] 12 Bit 
 	float t = *p_temperature;						// t:       Temperature [Ticks] 14 Bit
 	float rh_lin;									// rh_lin:  Humidity linear
	float rh_true;									// rh_true: Temperature compensated humidity
	float t_C;										// t_C   :  Temperature [癈]

	t_C = t*0.01 - 40;								//calc. temperature from ticks to [癈]
	rh_lin = C3*rh*rh + C2*rh + C1;					//calc. humidity from ticks to [%RH]
	rh_true = (t_C - 25)*(T1 + T2*rh) + rh_lin;		//calc. temperature compensated humidity [%RH]
	if(rh_true>100)
		rh_true = 100;								//cut if the value is outside of
	if(rh_true<0.1)
		rh_true = 0.1;								//the physical possible range

	*p_temperature=t_C;								//return temperature [癈]
	*p_humidity=rh_true;							//return humidity[%RH]
}

/****************************************************************
 *函数性质：公共
 *入口：humidity [%RH], temperature [癈]
 *出口：露点值
 *功能：// calculates dew point
 *调用方式：float calc_dewpoint(float h,float t)
*****************************************************************/
#if DEWPOINT == true
float calc_dewpoint(float h,float t)
{
	float logEx,dew_point;
	logEx = 0.66077 + 7.5*t/(237.3 + t) + (log10(h) - 2);
	dew_point = (logEx - 0.66077)*237.3/(0.66077+7.5-logEx);
	return dew_point;
}
#endif