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Read temperature & humidity for SHT25, SHT21 sensor

 
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wangine



Joined: 07 Jul 2009
Posts: 96
Location: Curtea de Arges, Romania

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Read temperature & humidity for SHT25, SHT21 sensor
PostPosted: Sat Sep 12, 2015 10:12 am     Reply with quote

The code was tested in a real hardware and simulated as well with 4 different sensors SHT21&SHT25 include (Chinese sensors). Code was tested in special chamber around other 3 home made hardware and 2 industrial calibrated devices for comparison.
Code don't have dependence of I2C port, can be use any pins. Range of OSC where has been tested is 4, 8 and 16MHz.
Single issue of code have a +0.02 error on humidity, example On 40.60 real humidity will show 40.00 humidity, but on 40.50 will show 40.52, that's it not a big deal, the sensor it self don't have that accuracy, but the idea is to don't put more errors in as code. Also i notice, SHT25 is more faster and accurate than SHT75 sensor, even the technical data look almost the same. The data line has tested above 1 meter, with decouple 100n cap on the end.
Code:
#include <18F4550.h>
#device ADC=16

#FUSES NOWDT                    //No Watch Dog Timer
#FUSES WDT128                   //Watch Dog Timer uses 1:128 Postscale
#FUSES NOBROWNOUT               //No brownout reset
#FUSES NOLVP                    //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOXINST                  //Extended set extension and Indexed Addressing mode disabled (Legacy mode)

//#use fast_io(B)
//#use delay(internal=8MHz)
//#USE RS232
//#use standard_io(B)

#use delay(crystal=8MHz)

extern void lcd_gotoxy(int8 x, int8 y);
extern void lcd_putc(char c);


SHT2x driver
Code:
/********************************************************************/
/*  Writer Tanase Bogdan                                           */
/*  (c) copyright www.wangine.ro                                   */
/*  ALL RIGHTS RESERVED                                             */
/*                                                                 */
/********************************************************************/
/* Ver 0.6 release 10/september/2015                                */
/********************************************************************/
/*Code will work with 4,8 and 16MHz oscillator, not tested above 16MHx*/
/*require pull up resistor 10k, on SDA/SCL line                    */
/********************************************************************/
//~~~~~~~~~~~~define I2C custom port~~~~~~~~~~~~~~~~~~~~~
#define sda_pin PIN_B0
#define scl_pin PIN_B1
//IIC
/*****************************Macro definition*****************************/
#define  SCL_H   output_high(scl_pin)
#define  SCL_L   output_low(scl_pin)
#define  SDA_H   output_high(sda_pin)
#define  SDA_L   output_low(sda_pin)

#define  SCL_out output_drive(scl_pin)       //Output Clock
#define  SDA_in  output_high(sda_pin)        //SDA change the input mode
#define  SDA_out output_drive(sda_pin)       //SDA output mode back
#define  SDA_val input_state(sda_pin)        //Bit value of SDA

#define ACK          0   //Reply
#define NACK         1   //Non-responders
#define SHT21ADDR    0x80

#define humid_comand 0xF5 // command reading humidity
#define temp_comand  0xF3 // command reading temperature

#define REG_wait     120
#define calibration  0.996018f

float temperature =  0;   // global temp variable
float humidity    =  0; // global humid variable
/*****************************************************************
[Function name] Start
[Function] to complete the operation starting condition IIC
[Parameters None
[Return value None
*****************************************************************/
void Start(void)
{
    SCL_out;
    SDA_out;

    SDA_H;
    SCL_H;
    delay_us(10);
    SDA_L;
    delay_us(10);
    SCL_L;
    delay_us(10);
}
/*****************************************************************
[Function name] Stop
[Function] to complete the operation termination condition IIC
[Parameters None
[Return value None
*****************************************************************/
void Stop(void)
{
    SCL_out;
    SDA_out;
    SCL_L;
    delay_us(10);
    SDA_L;
    delay_us(10);
    SDA_H;
    delay_us(10);
    SCL_H;
    delay_us(10);

}

/*****************************************************************
[Function name] Mack
[Function] to complete IIC host response operations
[Parameters None
[Return value None
*****************************************************************/
void Mack(void)
{
    SCL_out;
    SDA_out;
    SDA_L;
    delay_us(2);
    SCL_H;
    delay_us(10);
    SCL_L;
    delay_us(10);
    SDA_H;
    delay_us(10);
}
/*****************************************************************
[Function name] MNack
[Function] to complete non-response operations IIC hosts
[Parameters None
[Return value None
*****************************************************************/
void MNack(void)
{
    SCL_out;
    SDA_out;
    SDA_H;
    delay_us(2);
    SCL_H;
    delay_us(10);
    SCL_L;
    delay_us(2);
    SDA_L;
    delay_us(10);
}
/*****************************************************************
[Function name] Check
[Function] check from the answering machine's operation, 1-- there, no 0--
[Parameters None
[Return Value] ACK (acknowledge) or NACK (not acknowledge)
*****************************************************************/
unsigned char Check(void)
{
   int1 ack_q;

    SCL_out;
    SDA_out;
    SDA_H;
    delay_us(2);
    SCL_H;
    delay_us(2);
    SDA_in;
    delay_us(2);
    ack_q = SDA_val;   //??SDA??
    SCL_L;
    delay_us(10);
    SDA_out;
    if(ack_q)    return NACK;//1:???
    else       return ACK;
}
/*****************************************************************
[Function name] Write1
[Function] IIC bus sends a 1
[Parameters None
[Return value None
*****************************************************************/
void Write1(void)
{
    SCL_out;
    SDA_out;
    SCL_L;
    delay_us(10);

    SDA_H;
    delay_us(2);
    SCL_H;
    delay_us(10);
    SCL_L;
    delay_us(10);
}
/*****************************************************************
[Function name] Write0
[Function] sending a 0 to the IIC bus
[Parameters None
[Return value None
*****************************************************************/
void Write0(void)
{
    SCL_out;
    SDA_out;
    SCL_L;
    delay_us(10);

    SDA_L;
    delay_us(2);
    SCL_H;
    delay_us(10);
    SCL_L;
    delay_us(10);
}

/*****************************************************************
[Function name] WriteByte
[Function] to send a byte to the IIC bus
[Parameters] wdata for the data to be written
[Return Value] respond to the response signal returned from the machine
*****************************************************************/
unsigned char WriteByte(unsigned char wdata)
{
    unsigned char i,respond;
    SCL_out;
    SDA_out;

    for(i = 8;i > 0;i--)
    {
        if(wdata & 0x80)
            Write1();
        else
            Write0();
        wdata <<= 1;
    }
    SDA_H;
    delay_us(10);//_NOP();
    respond = Check();
    return respond;
}
/*****************************************************************
[Function name] ReadByte
[Function] to read a byte from the IIC bus
[Parameters None
[Return Value] rdata to read data
*****************************************************************/
unsigned char ReadByte(void)
{
    unsigned char  rdata = 0x01,i;
    int1 flag;
    SCL_out;
    //SDA_out;

    for(i = 0;i < 8;i++)
    {
        SDA_H;
        delay_us(2);//Delay();
        SCL_H;
        SDA_in;
        delay_us(10);//Delay();
        flag = SDA_val;
        rdata <<= 1;
        if(flag)
        {
            rdata |= 0x01;
        }
        SDA_out;
        SCL_L;
        delay_us(10);//Delay();
    }
    return rdata;
}
/*****************************************************************
[Function name] Read_temp and Read_humid
[Function] Sht21 measurement of temperature and humidity
Parameters  0xf3 measured temperature;  0xf5 measuring humidity
[Return Value] temperature, humidity
*****************************************************************/
void read_temp()
{
    float temp = 0;
    float T = 0;
    unsigned int8 MSB,LSB;
    Start();
    if(WriteByte(SHT21ADDR & 0xfe) == ACK)
    {

        if(WriteByte(temp_comand) == ACK)
        {
            do
            {
            delay_ms(REG_wait);
                Start();
            }
            while(WriteByte(SHT21ADDR | 0x01) == NACK);
            Stop();
               MSB = ReadByte();
            Mack();//IIC host response operations
               LSB = ReadByte();
            MNack();//IIC host non-response operation

            LSB &= 0xfc;// Two status bits, front and rear, LSB is conducting two physical computing must be set to '0'
            temp = MSB*256+LSB;

                T=0.26813*temp-4685;//TH=(175.72)*temp/65536.0-46.85;
                temperature = T / 100;
        }
    }
}
//********************************************************************
void read_humid()
{
    float temp = 0;
    float H = 0;
    unsigned int8 MSB,LSB;
    Start();
    if(WriteByte(SHT21ADDR & 0xfe) == ACK)
    {

        if(WriteByte(humid_comand) == ACK)
        {
            do
            {
            delay_ms(REG_wait);
                Start();
            }
            while(WriteByte(SHT21ADDR | 0x01) == NACK);
            Stop();
               MSB = ReadByte();
            Mack();//IIC host response operations
               LSB = ReadByte();
            MNack();//IIC host non-response operation

            LSB &= 0xfc;// Two status bits, front and rear, LSB is conducting two physical computing must be set to '0'
            temp = MSB*256+LSB;

                H = temp/65536.0 ;//0xC89F;
                humidity = (H * 125) - 6.50f ;   
            humidity *= calibration;
 //               humidity = (long int)(H*100)/100;//H =0.190735*temp-600;//TH = (temp*125.0)/65536.0-6;
        }
    }
}
//*****************************************************************************

and example how to use
Code:
#include <main4550.h>
#include <math.h>
#include </src/flex_lcd_20x2.c>
#include </src/__SHT21.c>
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int1 flag_sht = 1;
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#INT_RTCC
void  RTCC_isr(void)
{
                   WriteByte(0xFE); // in case if comunication is lost
   if(flag_sht == true)
      {
         read_temp();
         flag_sht = false;
      }
   else
      {
         read_humid();
         flag_sht = true;
      }
}
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
void main ()
   {   
   setup_timer_0(RTCC_INTERNAL|RTCC_DIV_4);      //262 ms overflow

   enable_interrupts(INT_RTCC);
   enable_interrupts(GLOBAL);
//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lcd_init();  // Always call this first.
delay_ms(10);   // Minimum 1 ms required after power-up.
   
   while (true)
      {
//   read_temp();
  lcd_gotoxy(1,1);
  printf(lcd_putc, "temperatura:%3.2f gC ", temperature );
//   read_humid();
  lcd_gotoxy(1,2);
  printf(lcd_putc, "umiditate  :%3.2f RH ", humidity );             
      }
   }
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