/*
Program : Read SHT11
Author : Somlak Mangnimit
Date : 16/11/2011
Device : PIC16F877 @20Mhz
*/
#include <htc.h>
#include <math.h>
#include <stdio.h>
#define _XTAL_FREQ 20000000
__CONFIG(FOSC_HS & WDTE_OFF & LVP_OFF);
#include "clcd.c"
#define SHT_SCK PORTBbits.RB4
#define SHT_DATA PORTBbits.RB5
#define SHT_SCK_DDR TRISBbits.TRISB4
#define SHT_DATA_DDR TRISBbits.TRISB5
#define SHT_SCK_LOW() SHT_SCK_DDR=0; SHT_SCK=0;
#define SHT_SCK_HIGH() SHT_SCK_DDR=0; SHT_SCK=1;
#define SHT_DATA_LOW() SHT_DATA_DDR=0; SHT_DATA=0;
#define SHT_DATA_HIGH() SHT_DATA_DDR=0; SHT_DATA=1;
#define SHT_DATA_FLOAT() SHT_DATA_DDR=1; SHT_DATA=0;
//SHT1x address=000 is currently supported
//SHT1x command code
//adr command r/w
#define SHT_STATUS_REG_W 0x06 //000 0011 0
#define SHT_STATUS_REG_R 0x07 //000 0011 1
#define SHT_MEASURE_TEMP 0x03 //000 0001 1
#define SHT_MEASURE_HUMI 0x05 //000 0010 1
#define SHT_RESET 0x1e //000 1111 0
//constant use for SHT1x Humidity Measurement
#define C1 -4.0
#define C2 +0.0405
#define C3 -0.0000028
//constant use for SHT1x Temperature Measurement
#define D1 -40.0
#define D2 +0.01
//constant use for SHT1x True Humidity Measurement
#define T1 +0.01
#define T2 +0.00008
//-----------
//delay usec
//-----------
void delay_us(unsigned int us){
while(--us){__delay_us(1);}
}
//-----------
//delay msec
//-----------
void delay_ms(unsigned int ms){
while(--ms){__delay_ms(1);}
}
//-----------------------------------
//SHT1x Transmission Start condition
//-----------------------------------
void SHTStart(void){
SHT_DATA_HIGH(); //Initial state
SHT_SCK_LOW();
delay_us(2);
SHT_SCK_HIGH();
delay_us(1);
SHT_DATA_LOW();
delay_us(1);
SHT_SCK_LOW();
delay_us(2);
SHT_SCK_HIGH();
delay_us(1);
SHT_DATA_HIGH();
delay_us(1);
SHT_SCK_LOW();
}
//-----------------------
//SHT1x Connection Reset
//-----------------------
void SHTConReset(void){
unsigned char i;
SHT_DATA_HIGH();
SHT_SCK_LOW();
delay_us(2);
for(i=0;i<9;i++){ //9 SCK cycles
SHT_SCK_HIGH();
delay_us(2);
SHT_SCK_LOW();
delay_us(2);
}
SHTStart();
delay_ms(250);
}
//----------------------------------------------
//SHT1x Address & Command Mode with address=000
//----------------------------------------------
unsigned char SHTWrite(unsigned char Data){
unsigned char i;
for (i=0x80;i>0;i/=2){ //shift bit for masking data
delay_us(1);
if(i&Data){SHT_DATA_HIGH();}
else{SHT_DATA_LOW();}
delay_us(1); //Snend Clock each bit
SHT_SCK_HIGH();
delay_us(2);
SHT_SCK_LOW();
}
SHT_DATA_FLOAT(); //Change DATA Line to Input
delay_us(2);
SHT_SCK_HIGH(); //Clock for Acknowledge
delay_us(2);
i = SHT_DATA; //Get Acknowledge
SHT_SCK_LOW();
delay_ms(250);
return(i);
}
//---------------------
//Read data from SHT1x
//---------------------
long SHTRead(void){
long lTmp,lValue,lVal1=0,lVal2=0;
unsigned char i;
//get MSB from SHT1x
SHT_DATA_FLOAT(); //Change to Input
for(i=0;i<8;i++){
lVal1<<=1;
delay_us(1);
SHT_SCK_HIGH(); //Send Clock Hight
delay_us(1);
lTmp = SHT_DATA; //Read Data Bit
delay_us(1);
SHT_SCK_LOW(); //Send Clock Low
delay_us(1);
if(lTmp){lVal1|=1;} //store in lVal1
}
//Acknowledge for Next byte
SHT_DATA_LOW();
delay_us(1);
SHT_SCK_HIGH();
delay_us(2);
SHT_SCK_LOW();
delay_us(1);
//get LSB from SHT1x
SHT_DATA_FLOAT(); //Change to Input
for(i=0;i<8;i++){
lVal2<<=1;
delay_us(1);
SHT_SCK_HIGH(); //Send Clock Hight
delay_us(1);
lTmp = SHT_DATA; //Read Data Bit
delay_us(1);
SHT_SCK_LOW(); //Send Clock Low
delay_us(1);
if(lTmp){lVal2|=1;} //store in lVal2
}
//noAcknowledge
SHT_DATA_HIGH();
delay_us(1);
SHT_SCK_HIGH();
delay_us(2);
SHT_SCK_LOW();
//Makes a 16 bit number out of two 8 bit numbers.
lValue = (unsigned int)(lVal1&0xff)*0x100+(lVal2&0xff);
return(lValue);
}
//-------------------------------------------------------------------
//SHT1x Soft Reset
//resets the interface, clears the status register to default values
//wait minimum 11ms before next command
//-------------------------------------------------------------------
void SHTSoftReset(void){
SHTConReset();
SHTWrite(SHT_RESET);
}
unsigned char buffer[20];
void clr_buffer(void){
char x;
for(x=0;x<20;x++){buffer[x]=0x20;}
}
//-------------
//Main Program
//-------------
void main(void){
long lValue_rh,lValue_temp,Status_reg;
float fRh_lin,fRh_true,fTemp_true,fDew_point,fLogEW;
unsigned char ER;
TRISB = 0b11110000;
TRISC = 0b11111000;
SHTConReset();
lcd_init();
SHTStart();
SHTWrite(SHT_STATUS_REG_R);
Status_reg = SHTRead();
Status_reg = (int)Status_reg;
if((Status_reg&0x007)!=0){
SHTStart();
SHTWrite(SHT_STATUS_REG_W);
SHTWrite(0x00);
}
delay_ms(12);
while(1){
SHTStart(); //start transmission
ER = SHTWrite(SHT_MEASURE_TEMP); //measure temperature
if(ER==1){
lcd_write_command(0x01);
lcd_gotoxy(0,0);
lcd_print_string("-----[ SHT-11 ]-----");
lcd_gotoxy(1,0);
lcd_print_string("Sensor Error!");
delay_ms(1000);
continue;
}
lValue_temp = SHTRead();
fTemp_true = D1+(D2*lValue_temp); //temperature calculation
//delay 11ms before next command
delay_ms(12);
SHTStart(); //start transmission
SHTWrite(SHT_MEASURE_HUMI); //measure relative humidity
lValue_rh = SHTRead();
//relative humidity calculation
fRh_lin = C1+(C2*lValue_rh)+(C3*lValue_rh*lValue_rh);
fRh_true = (fTemp_true-25)*(T1+(T2*lValue_rh))+fRh_lin;
if(fRh_true>100.0){fRh_true = 100.0;}
if(fRh_true<0.1){fRh_true = 0.1;}
//dewpoint calculation
fLogEW = ((log10(fRh_true)-2)/0.4343)+(17.62*fTemp_true)/(243.12+fTemp_true);
fDew_point = (243.12*fLogEW)/(17.62-fLogEW);
lcd_gotoxy(0,0);
lcd_print_string("-----[ SHT-11 ]-----");
lcd_gotoxy(1,0);
clr_buffer();
sprintf(buffer,"Temperature :%3.1f C",fTemp_true);
lcd_print_string(buffer);
lcd_gotoxy(2,0);
clr_buffer();
sprintf(buffer,"Humidity :%3.1f %%",fRh_true);
lcd_print_string(buffer);
lcd_gotoxy(3,0);
clr_buffer();
sprintf(buffer,"Dewpoint :%3.1f C",fDew_point);
lcd_print_string(buffer);
delay_ms(1000);
}
}
