void Delay(long nCount)
{
/* Decrement nCount value */
while (nCount != 0)
{
nCount--;
}
}
//----------------------------------------------------------------------------------
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) DS_DATA_H(); //masking value with i , write to SENSI-BUS
else DS_DATA_L();
DS_CLK_H(); //clk for SENSI-BUS
Delay(2);Delay(2);Delay(2); //pulswith approx. 5 us
DS_CLK_L();
}
DS_DATA_H(); //release DATA-line
SHT_DATA_IN;
DS_CLK_H(); //clk #9 for ack
error=DS_DATA_STATE; //check ack (DATA will be pulled down by SHT11)
DS_CLK_L();
Delay(2);
SHT_DATA_OUT;
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;
SHT_DATA_OUT;
DS_DATA_H(); //release DATA-line
SHT_DATA_IN;
for (i=0x80;i>0;i/=2) //shift bit for masking
{ DS_CLK_H(); //clk for SENSI-BUS
if (DS_DATA_STATE) val=(val | i); //read bit
DS_CLK_L();
}
SHT_DATA_OUT;
//DS_DATA_STATE=!ack; //in case of "ack==1" pull down DATA-Line
if(ack==1)
{
//----------------------------------------------------------------------------------
void s_connectionreset(void)
//----------------------------------------------------------------------------------
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
// _____________________________________________________ ________
// DATA: |_______|
// _ _ _ _ _ _ _ _ _ ___ ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______
{
unsigned char i;
DS_DATA_H(); DS_CLK_L(); //Initial state
for(i=0;i<9;i++) //9 SCK cycles
{ DS_CLK_H();
DS_CLK_L();
}
s_transstart(); //transmission start
}
//----------------------------------------------------------------------------------
char s_measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode)
//----------------------------------------------------------------------------------
// makes a measurement (humidity/temperature) with checksum
{
unsigned 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;
}
SHT_DATA_IN;
for (i=0;i<65535;i++) if(DS_DATA_STATE==0) break; //wait until sensor has finished the measurement
if(DS_DATA_STATE) 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
SHT_DATA_OUT;
return error;
}
//----------------------------------------------------------------------------------------
void calc_sth11(float *p_humidity ,float *p_temperature)
//----------------------------------------------------------------------------------------
// calculates temperature [C] and humidity [%RH]
// input : humi [Ticks] (12 bit)
// temp [Ticks] (14 bit)
// output: humi [%RH]
// temp [C]
{ 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 [C]
//t_C=t*0.01 – 40; //calc. Temperature from ticks to [C]
t_C=t*0.01;
t_C=t_C-40;
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 [C]
*p_humidity=rh_true; //return humidity[%RH]
}
//----------------------------------------------------------------------------------
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 [C]
// 4. calculate dew point [C]
// 5. print temperature, humidity, dew point
{
value humi_val,temp_val;
unsigned char error,checksum;
unsigned int i;
SHT_Init();
s_connectionreset();
while(1)
{
//s_transstart();
//s_write_byte(0x03);
error=0;
error+=s_measure((unsigned char*) &humi_val.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
Delay(2);
}
printf("temp:%3.1f humi:%3.1f",temp_val.f,humi_val.f);
//----------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!)
//-----------------------------------------------------------------------------------
}