[PIC] PIC16F1827 and SHTxx, problem when read the value(not change)

[truong_giang2211]

Hi everyone,

I am newer.
As below is my code+hex file and simulate circuit in Protues7.8. I am using CCS V5.xx
I finished my project when i use PIC16f877a.
But when i copy code(i just changed PIN DATA and SCK), it can work, but the value of temperature not change(update) ? Reason why ??

Thanks for your read !

My code:

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///////////////////////////////////////////////////////////////
#include <16F1827.h>
//#DEVICE ADC=8
#include <stdio.h> 
#include <math.h>
#FUSES NOWDT, HS, NOPUT, PROTECT, NODEBUG, NOBROWNOUT, NOLVP
#use delay(clock = 4000000) 
#USE RS232(baud=2400, xmit=PIN_B5, rcv=PIN_B2)
#define sht_data_pin   PIN_B7
#define sht_clk_pin    PIN_B6
#define LED    PIN_B0
#define LED1   PIN_B3
 
 
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 
} 
 
 
// 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); 
} 
 
 
// 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); 
     } 
} 
 
 
// 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();            //say to 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); 
} 
 
 
//calculate SHT75 temp & RH 
 
void calculate_data (int16 temp, int16 humid, float & tc, float & rhlin, float & rhtrue) 
{ 
    float  rh; 
    //float truehumid1; 
   
    //calculate temperature reading 
    tc = ((float) temp * 0.01) - 40.0; 
   
    //calculate Real RH reading 
    rh = (float) humid; 
    
   // rh linear
    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 
}
//=====================================
 
//=====================================
void main(void) 
{ 
    float restemp, truehumid;  
    sht_init(); 
    delay_ms(200);
    long a[30]={0x00,0xff,0xff,0x00,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B};
  
   // int so1=0,so2=0;
    
    while(TRUE) 
    { 
       delay_ms(100);
       sht_rd (restemp, truehumid);         
       a[4]= restemp;
       putc(restemp);
       delay_ms(500);
       output_toggle(LED);
     delay_ms(200);        //delay 200 ms between reading to prevent self heating of sensor 
    } 
} 
///////////////////////////////////////////////////////////////

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[Tanmay Dash]

1> while conversion process in adc the chip must be disselected .
2>after conversion the clk signal must be low to fetch the converted data
3> after this the chip is deselected and step 1 is repeated again
in this way ur temperature sensor data will be updated


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[truong_giang2211]

Dear Tanmay Dash,

Thanks for your answer.

According datasheet, SHTxx provide digital interface with MCU, no need ADC module. So in this case, i dont use ADC to convert signal into digital as you think.

In here MCU send clock to SHTxx and then SHTxx will receive and feedback to MCU.

File attach is datasheet of SHTxx sensor.

 

[Tanmay Dash]

dear truang,
after going trhrough the document that u have attached(shtxx) i came to know the following things.plz check that if u have implement the things in ur program--
1 > after start up shtxx takes 11ms .so provide a delay of 11ms
2> then u have to start communication by initiating transmission sequence-make clk line high then lower the dataline, followed by pulling low clock line and then raising the data line.
3> after the 8bit rception the acknowledgement is given by the shtxx by lowering the data..plz check the ack
4> after sucessful ack....user should make the data line high at 9th clk pulse
in this way u can get ur output..
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