CCS C Software and Maintenance Offers
FAQFAQ   FAQForum Help   FAQOfficial CCS Support   SearchSearch  RegisterRegister 

ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to support@ccsinfo.com

Read temperature & humidity for SHT25, SHT21 sensor

 
Post new topic   Reply to topic    CCS Forum Index -> Code Library
View previous topic :: View next topic  
Author Message
wangine



Joined: 07 Jul 2009
Posts: 98
Location: Curtea de Arges, Romania

View user's profile Send private message Send e-mail Yahoo Messenger

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 );             
      }
   }
Display posts from previous:   
Post new topic   Reply to topic    CCS Forum Index -> Code Library All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group