SHT75 Humidity and Temperature Sensor

 

SHT75 bağıl nem ve sıcaklık bilgisi veren sensördür. Kullanımı için gerekli olan driver ve uygulama kodları aşağıda verilmiştir.

Driver kodları

///////////////////////////////////////////////////////////////////////////////
// //
// Driver file for SHT75 Temperature & Humidity Sensor //
// //
// ***** To initialise SHT75 sensor upon power up ***** //
// //
// Function : sht_init() //
// Return : none //
// //
// //
// ***** To measure and caluculate SHT75 temp & real RH ***** //
// //
// Function : sht_rd (temp, truehumid) //
// Return : temperature & true humidity in float values //
// //
///////////////////////////////////////////////////////////////////////////////

#define sht_data_pin PIN_c1
#define sht_clk_pin PIN_C0



//***** Function to alert SHT75 *****

void comstart (void)
{
output_float(sht_data_pin); //data high
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_bit(sht_data_pin, 0); //data low
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
delay_us(2);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_float(sht_data_pin); //data high
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
}


//***** Function to write data to SHT75 *****

int1 comwrite (int8 iobyte)
{
int8 i, mask = 0x80;
int1 ack;

//Shift out command
delay_us(4);
for(i=0; i<8; i++)
{
output_bit(sht_clk_pin, 0); //clk low
if((iobyte & mask) > 0) output_float(sht_data_pin); //data high if MSB high
else output_bit(sht_data_pin, 0); //data low if MSB low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
mask = mask >> 1; //shift to next bit
}

//Shift in ack
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
ack = input(sht_data_pin); //get ack bit
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
output_bit(sht_clk_pin, 0); //clk low
return(ack);
}


//***** Function to read data from SHT75 *****

int16 comread (void)
{
int8 i;
int16 iobyte = 0;
const int16 mask0 = 0x0000;
const int16 mask1 = 0x0001;

//shift in MSB data
for(i=0; i<8; i++)
{
iobyte = iobyte << 1;
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
else iobyte |= mask0;
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
}

//send ack 0 bit
output_bit(sht_data_pin, 0); //data low
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(2);
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
output_float(sht_data_pin); //data high

//shift in LSB data
for(i=0; i<8; i++)
{
iobyte = iobyte << 1;
output_bit(sht_clk_pin, 1); //clk high
delay_us(1);
if (input(sht_data_pin)) iobyte |= mask1; //shift in data bit
else iobyte |= mask0;
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
}

//send ack 1 bit
output_float(sht_data_pin); //data high
delay_us(1);
output_bit(sht_clk_pin, 1); //clk high
delay_us(2);
output_bit(sht_clk_pin, 0); //clk low

return(iobyte);
}



//***** Function to wait for SHT75 reading *****

void comwait (void)
{
int16 sht_delay;

output_float(sht_data_pin); //data high
output_bit(sht_clk_pin, 0); //clk low
delay_us(1);
for(sht_delay=0; sht_delay<30000; sht_delay++) // wait for max 300ms
{
if (!input(sht_data_pin)) break; //if sht_data_pin low, SHT75 ready
delay_us(10);
}
}



//***** Function to reset SHT75 communication *****

void comreset (void)
{
int8 i;

output_float(sht_data_pin); //data high
output_bit(sht_clk_pin, 0); //clk low
delay_us(2);
for(i=0; i<9; i++)
{
output_bit(sht_clk_pin, 1); //toggle clk 9 times
delay_us(2);
output_bit(sht_clk_pin, 0);
delay_us(2);
}
comstart();
}



//***** Function to soft reset SHT75 *****

void sht_soft_reset (void)
{
comreset(); //SHT75 communication reset
comwrite(0x1e); //send SHT75 reset command
delay_ms(15); //pause 15 ms
}



//***** Function to measure SHT75 temperature *****

int16 measuretemp (void)
{
int1 ack;
int16 iobyte;

comstart(); //alert SHT75
ack = comwrite(0x03); //send measure temp command and read ack status
if(ack == 1) return;
comwait(); //wait for SHT75 measurement to complete
iobyte = comread(); //read SHT75 temp data
return(iobyte);
}



//***** Function to measure SHT75 RH *****

int16 measurehumid (void)
{
int1 ack;
int16 iobyte;

comstart(); //alert SHT75
ack = comwrite(0x05); //send measure RH command and read ack status
if(ack == 1) return;
comwait(); //wait for SHT75 measurement to complete
iobyte = comread(); //read SHT75 temp data
return(iobyte);
}



//***** Function to calculate SHT75 temp & RH *****

void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue)
{
float truehumid1, rh;

//calculate temperature reading
tc = ((float) temp * 0.01) - 40.0;

//calculate Real RH reading
rh = (float) humid;

rhlin = (rh * 0.0405) - (rh * rh * 0.0000028) - 4.0;

//calculate True RH reading
rhtrue = ((tc - 25.0) * (0.01 + (0.00008 * rh))) + rhlin;
}



//***** Function to measure & calculate SHT75 temp & RH *****

void sht_rd (float & temp, float & truehumid)
{
int16 restemp, reshumid;
float realhumid;
restemp = 0; truehumid = 0;

restemp = measuretemp(); //measure temp
reshumid = measurehumid(); //measure RH
calculate_data (restemp, reshumid, temp, realhumid, truehumid); //calculate temp & RH
}



//***** Function to initialise SHT75 on power-up *****

void sht_init (void)
{
comreset(); //reset SHT75
delay_ms(20); //delay for power-up
}

Örnek Uygulama programı

#include <16F876A.h>
#fuses HS,NOWDT,PUT,NOPROTECT,NOLVP
#use delay(clock=20000000)

#include <lcd.c>
#include <sht75.c>

void main()
{
float restemp, truehumid;
lcd_init();
sht_init();

while(1)
{
sht_rd (restemp, truehumid);
lcd_gotoxy(1,1);
printf(lcd_putc, "Temp : %3.1f %cC ", restemp, 223);
printf(lcd_putc, "\nRH : %3.1f %% ", truehumid);
delay_ms(500); //delay 500 ms between reading to prevent self heating of sensor
}
}
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