/***********************************************************************************
Project: SHT1x/7x demo program (V2.4)
Filename: SHT1x_sample_code.c
Prozessor: 80C51 family
Compiler: Keil Version 6.23a
Autor: MST
Copyrigth: (c) Sensirion AG
***********************************************************************************/
// Revisions:
// V2.4 calc_sht11() Coefficients for humidity and temperature conversion
// changed (for V4 sensors)
// calc_dewpoint() New formula for dew point calculation
#include <AT89s53.h> //Microcontroller specific library, e.g. port definitions
#include <intrins.h> //Keil library (is used for _nop()_ operation)
#include <math.h> //Keil library
#include <stdio.h> //Keil library
typedef union
{ unsigned int i;
float f;
} value;
//----------------------------------------------------------------------------------
// modul-var
//----------------------------------------------------------------------------------
enum {TEMP,HUMI};
#define DATA P1_1
#define SCK P1_0
#define noACK 0
#define ACK 1
//adr command r/w
#define STATUS_REG_W 0x06 //000 0011 0
#define STATUS_REG_R 0x07 //000 0011 1
#define MEASURE_TEMP 0x03 //000 0001 1
#define MEASURE_HUMI 0x05 //000 0010 1
#define RESET 0x1e //000 1111 0
//----------------------------------------------------------------------------------
char s_write_byte(unsigned char value)
//----------------------------------------------------------------------------------
// writes a byte on the Sensibus and checks the acknowledge
{
unsigned char i,error=0;
for (i=0x80;i>0;i/=2) //shift bit for masking
{ if (i & value) DATA=1; //masking value with i , write to SENSI-BUS
else DATA=0;
_nop_(); //observe setup time
SCK=1; //clk for SENSI-BUS
_nop_();_nop_();_nop_(); //pulswith approx. 5 us
SCK=0;
_nop_(); //observe hold time
}
DATA=1; //release DATA-line
_nop_(); //observe setup time
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
}
//----------------------------------------------------------------------------------
char s_read_byte(unsigned char ack)
//----------------------------------------------------------------------------------
// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
{
unsigned char i,val=0;
DATA=1; //release DATA-line
for (i=0x80;i>0;i/=2) //shift bit for masking
{ SCK=1; //clk for SENSI-BUS
if (DATA) val=(val | i); //read bit
SCK=0;
}
DATA=!ack; //in case of "ack==1" pull down DATA-Line
_nop_(); //observe setup time
SCK=1; //clk #9 for ack
_nop_();_nop_();_nop_(); //pulswith approx. 5 us
SCK=0;
_nop_(); //observe hold time
DATA=1; //release DATA-line
return val;
}
//----------------------------------------------------------------------------------
void s_transstart(void)
//----------------------------------------------------------------------------------
// generates a transmission start
// _____ ________
// 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;
}
//----------------------------------------------------------------------------------
void s_connectionreset(void)
//----------------------------------------------------------------------------------
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
// _____________________________________________________ ________
// DATA: |_______|
// _ _ _ _ _ _ _ _ _ ___ ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______
{
unsigned char i;
DATA=1; SCK=0; //Initial state
for(i=0;i<9;i++) //9 SCK cycles
{ SCK=1;
SCK=0;
}
s_transstart(); //transmission start
}
//----------------------------------------------------------------------------------
char s_softreset(void)
//----------------------------------------------------------------------------------
// resets the sensor by a softreset
{
unsigned char error=0;
s_connectionreset(); //reset communication
error+=s_write_byte(RESET); //send RESET-command to sensor
return error; //error=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_read_statusreg(unsigned char *p_value, unsigned char *p_checksum)
//----------------------------------------------------------------------------------
// reads the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error=s_write_byte(STATUS_REG_R); //send command to sensor
*p_value=s_read_byte(ACK); //read status register (8-bit)
*p_checksum=s_read_byte(noACK); //read checksum (8-bit)
return error; //error=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_write_statusreg(unsigned char *p_value)
//----------------------------------------------------------------------------------
// writes the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error+=s_write_byte(STATUS_REG_W);//send command to sensor
error+=s_write_byte(*p_value); //send value of status register
return error; //error>=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode)
//----------------------------------------------------------------------------------
// makes a measurement (humidity/temperature) with checksum
{
unsigned char error=0;
unsigned int i;
s_transstart(); //transmission start
switch(mode){ //send command to sensor
case TEMP : error+=s_write_byte(MEASURE_TEMP); break;
case HUMI : error+=s_write_byte(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+=1; // or timeout (~2 sec.) is reached
*(p_value) =s_read_byte(ACK); //read the first byte (MSB)
*(p_value+1)=s_read_byte(ACK); //read the second byte (LSB)
*p_checksum =s_read_byte(noACK); //read checksum
return error;
}
//----------------------------------------------------------------------------------
void init_uart()
//----------------------------------------------------------------------------------
//9600 bps @ 11.059 MHz
{SCON = 0x52;
TMOD = 0x20;
TCON = 0x69;
TH1 = 0xfd;
}
//----------------------------------------------------------------------------------------
void calc_sth11(float *p_humidity ,float *p_temperature)
//----------------------------------------------------------------------------------------
// calculates temperature [癈] and humidity [%RH]
// input : humi [Ticks] (12 bit)
// temp [Ticks] (14 bit)
// output: humi [%RH]
// temp [癈]
{ const float C1=-2.0468; // for 12 Bit RH
const float C2=+0.0367; // for 12 Bit RH
const float C3=-0.0000015955; // for 12 Bit RH
const float T1=+0.01; // for 12 Bit RH
const float T2=+0.00008; // for 12 Bit RH
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 - 40.1; //calc. temperature [癈] from 14 bit temp. ticks @ 5V
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]
}
//--------------------------------------------------------------------
float calc_dewpoint(float h,float t)
//--------------------------------------------------------------------
// calculates dew point
// input: humidity [%RH], temperature [癈]
// output: dew point [癈]
{ float k,dew_point ;
k = (log10(h)-2)/0.4343 + (17.62*t)/(243.12+t);
dew_point = 243.12*k/(17.62-k);
return dew_point;
}
//----------------------------------------------------------------------------------
void main()
//----------------------------------------------------------------------------------
// sample program that shows how to use SHT11 functions
// 1. connection reset
// 2. measure humidity [ticks](12 bit) and temperature [ticks](14 bit)
// 3. calculate humidity [%RH] and temperature [癈]
// 4. calculate dew point [癈]
// 5. print temperature, humidity, dew point
{ value humi_val,temp_val;
float dew_point;
unsigned char error,checksum;
unsigned int i;
init_uart();
s_connectionreset();
while(1)
{ error=0;
error+=s_measure((unsigned char*) &humi_valvalu.i,&checksum,HUMI); //measure humidity
error+=s_measure((unsigned char*) &temp_val.i,&checksum,TEMP); //measure temperature
if(error!=0) s_connectionreset(); //in case of an error: connection reset
else
{ humi_val.f=(float)humi_val.i; //converts integer to float
temp_val.f=(float)temp_val.i; //converts integer to float
calc_sth11(&humi_val.f,&temp_val.f); //calculate humidity, temperature
dew_point=calc_dewpoint(humi_val.f,temp_val.f); //calculate dew point
printf("temp:%5.1fC humi:%5.1f%% dew point:%5.1fC\n",temp_val.f,humi_val.f,dew_point);
}
//----------wait approx. 0.8s to avoid heating up SHTxx------------------------------
for (i=0;i<40000;i++); //(be sure that the compiler doesn't eliminate this line!)
//-----------------------------------------------------------------------------------
}
}
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