Problem In Reading Data From SHT11 By ATMEGA32

[bolandgoo]

Hi,
I want to read temperature and humidity data from SHT11 by ATMEGA32. I use Code Vision compiler. The hardware is based on Figure 10 in the SHT11 datasheet.
The source code that I found was related to AT89s53 microcontroller. I changed something to prepare it to use with ATMEGA32. However the code had some errors that I think they don’t related to the kind of microcontroller. Here are some:
1) The “value” variable in the “s_write_byte” function cause an error.
After I changed this name to another, the compiler can compile it without any error.
2) I think the statement “if (error! = 0) “in the while is true every time and so I can’t read the data. After I changed it to “if (error==0) “the data replied.
3) The compiler has two important Warning. It says:
a) local variable ‘humi_val’ is used before it’s value is set.
b) local variable ‘temp_val’ is used before it’s value is set.
I was wondering if anybody would mind helping me to solve the problem.
Finally, I want to know, how can I translate the data that SHT11 will response to temperature and humidity? For example in the page 7 of its data sheet we can see 1073(Hex) equals 35.50% RH. How? What about temperature?
Thanks

 

[bigdogguru]

Can you upload or post your code? We need to see your code before we can help you correct any errors.

---------- Post added at 04:24 ---------- Previous post was at 04:02 ----------

Finally, I want to know, how can I translate the data that SHT11 will response to temperature and humidity? For example in the page 7 of its data sheet we can see 1073(Hex) equals 35.50% RH. How? What about temperature?

Here are some projects which use the SHT11 with an AVR ATMEGA:

**broken link removed**

Temperature and humidity measurements with the AVR web-server

This example project is written in BASIC.
However it should be fairly easy for you to adapt the section which reads the SHTII and converts the reading to a meaningful value:

AN #116 - Reading the SHT11 Humidity sensor

After we see your code, we can help you further.

BigDog

 

[bolandgoo]

Thnx, here is my code:


#include <mega32.h>
#include <delay.h>
#include <math.h>
#include <stdio.h>
typedef union
{
unsigned int i;
float f;
}
value;
enum {TEMP,HUMI};
#define DATA PORTC.1
#define SCK PORTC.0
#define noACK 0
#define ACK 1
//adr command r/w
#define STATUS_REG_W 0x06 //000 0011 0
#define STATUS_REG_R 0x07 //000 0011 1
#define MEASURE_TEMP 0x03 //000 0001 1
#define MEASURE_HUMI 0x05 //000 0010 1
#define RESET 0x1e //000 1111 0
#define FOSC 8000000// Clock Speed
#define BAUD 9600
#define MYUBRR (FOSC/(16*BAUD))-1
#define CR 0X0D
#define LF 0X0A
//*************************************************************************************
char s_write_byte (unsigned char value)
// writes a byte on the Sensibus and checks the acknowledge
{
unsigned char i,error=0;
for (i=0x80;i>0;i/=2) //shift bit for masking
{
if (i & value) DATA=1; //masking value with i , write to SENSI-BUS
else DATA=0;
SCK=1; //clk for SENSI-BUS
//_nop_();_nop_();_nop_(); //pulswith approx. 5 us
delay_us(5);
SCK=0;
}
DATA=1; //release DATA-line
SCK=1; //clk #9 for ack
error=DATA; //check ack (DATA will be pulled down by SHT11)
SCK=0;
return error; //error=1 in case of no acknowledge
}
//*************************************************************************************
char s_read_byte(unsigned char ack)
// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
{
unsigned char i,val=0;
DATA=1; //release DATA-line
for (i=0x80;i>0;i/=2) //shift bit for masking
{
SCK=1; //clk for SENSI-BUS
if (DATA) val=(val | i); //read bit
SCK=0;
}
DATA=!ack; //in case of "ack==1" pull down DATA-Line
SCK=1; //clk #9 for ack
//_nop_();_nop_();_nop_(); //pulswith approx. 5 us
delay_us(5);
SCK=0;
DATA=1; //release DATA-line
return val;
}
//*************************************************************************************
void s_transstart(void)
// generates a transmission start
// _____ ________
// DATA: |_______|
// ___ ___
// SCK : ___| |___| |______
{
DATA=1; SCK=0; //Initial state
//_nop_();
delay_us(2);
SCK=1;
//_nop_();
delay_us(2);
DATA=0;
//_nop_();
delay_us(2);
SCK=0;
//_nop_();_nop_();_nop_();
delay_us(5);
SCK=1;
//_nop_();
delay_us(2);
DATA=1;
//_nop_();
delay_us(2);
SCK=0;
}
//*************************************************************************************
void s_connectionreset(void)
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
// _____________________________________________________ ________
// DATA: |_______|
// _ _ _ _ _ _ _ _ _ ___ ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______
{
unsigned char i;
DATA=1; SCK=0; //Initial state
for(i=0;i<9;i++) //9 SCK cycles
{ SCK=1;
SCK=0;
}
s_transstart(); //transmission start
}
//*************************************************************************************
char s_softreset(void)
// resets the sensor by a softreset
{
unsigned char error=0;
s_connectionreset(); //reset communication
error+=s_write_byte(RESET); //send RESET-command to sensor
return error; //error=1 in case of no response form the sensor
}
//*************************************************************************************
char s_read_statusreg(unsigned char *p_value, unsigned char *p_checksum)
// reads the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error=s_write_byte(STATUS_REG_R); //send command to sensor
*p_value=s_read_byte(ACK); //read status register (8-bit)
*p_checksum=s_read_byte(noACK); //read checksum (8-bit)
return error; //error=1 in case of no response form the sensor
}
//*************************************************************************************
char s_write_statusreg(unsigned char *p_value)
// writes the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error+=s_write_byte(STATUS_REG_W);//send command to sensor
error+=s_write_byte(*p_value); //send value of status register
return error; //error>=1 in case of no response form the sensor
}
//*************************************************************************************
char s_measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode)
// makes a measurement (humidity/temperature) with checksum
{
unsigned error=0;
unsigned int i;
s_transstart(); //transmission start
switch(mode)
{ //send command to sensor
case TEMP : error+=s_write_byte(MEASURE_TEMP); break;
case HUMI : error+=s_write_byte(MEASURE_HUMI); break;
default : break;
}
for (i=0;i<65535;i++) if(DATA==0) break; //wait until sensor has finished the measurement
if(DATA) error+=1; // or timeout (~2 sec.) is reached
*(p_value) =s_read_byte(ACK); //read the first byte (MSB)
*(p_value+1)=s_read_byte(ACK); //read the second byte (LSB)
*p_checksum =s_read_byte(noACK); //read checksum
return error;
}
//*************************************************************************************
void calc_sth11(float *p_humidity ,float *p_temperature)
// calculates temperature [C] and humidity [%RH]
// input : humi [Ticks] (12 bit)
// temp [Ticks] (14 bit)
// output: humi [%RH]
// temp [C]
{
const float C1=-4.0; // for 12 Bit
const float C2= 0.0405; // for 12 Bit
const float C3=-0.0000028; // for 12 Bit
const float T1=0.01; // for 14 Bit @ 5V
const float T2=0.00008; // for 14 Bit @ 5V
float rh=*p_humidity; // rh: Humidity [Ticks] 12 Bit
float t=*p_temperature; // t: Temperature [Ticks] 14 Bit
float rh_lin; // rh_lin: Humidity linear
float rh_true; // rh_true: Temperature compensated humidity
float t_C; // t_C : Temperature [C]
t_C=t*0.01-40; //calc. Temperature from ticks to [C]
rh_lin=C3*rh*rh + C2*rh + C1; //calc. Humidity from ticks to [%RH]
rh_true=(t_C-25)*(T1+T2*rh)+rh_lin; //calc. Temperature compensated humidity [%RH]
if(rh_true>100)rh_true=100; //cut if the value is outside of
if(rh_true<0.1)rh_true=0.1; //the physical possible range
*p_temperature=t_C; //return temperature [C]
*p_humidity=rh_true; //return humidity[%RH]
}
//*************************************************************************************
float calc_dewpoint(float h,float t)
// calculates dew point
// input: humidity [%RH], temperature [C]
// output: dew point [C]
{
float k,dew_point ;
k = (log10(h)-2)/0.4343 + (17.62*t)/(243.12+t);
dew_point = 243.12*k/(17.62-k);
return dew_point;
}
//*************************************************************************************
void USART_Init(unsigned int ubrr)
{
UCSRA=0X00;
UBRRH = (unsigned char)(ubrr>>8); // Set baud rate//
UBRRL = (unsigned char)ubrr;
UCSRB = 0X08; // Enable Transmitter//
UCSRC = 0B10000110; // Set frame format: 8data, 1stop bit//
}
//*************************************************************************************
void USART_Transmit(unsigned char info)
{
while ((UCSRA & 0b00100000)!=0b00100000); // Wait for empty transmit buffer //
UDR = info; // Put data into buffer, sends the data//
}
//*************************************************************************************
void main()
// sample program that shows how to use SHT11 functions
// 1. connection reset
// 2. measure humidity [ticks](12 bit) and temperature [ticks](14 bit)
// 3. calculate humidity [%RH] and temperature [C]
// 4. calculate dew point [C]
// 5. print temperature, humidity, dew point
{
value humi_val,temp_val;
float dew_point;
unsigned char error,checksum;
unsigned int i;
DDRC.0=1;
//init_uart();
USART_Init(MYUBRR);
s_connectionreset();
while(1)
{
error=0;
error+=s_measure((unsigned char*) &humi_val.i,&checksum,HUMI); //measure humidity
error+=s_measure((unsigned char*) &temp_val.i,&checksum,TEMP); //measure temperature
if(error!=0) s_connectionreset(); //in case of an error: connection reset
else
{
humi_val.f=(float)humi_val.i; //converts integer to float
temp_val.f=(float)temp_val.i; //converts integer to float
calc_sth11(&humi_val.f,&temp_val.f); //calculate humidity, temperature
dew_point=calc_dewpoint(humi_val.f,temp_val.f); //calculate dew point
//send final data to serial interface (USART)
printf(“temp:%5.1fC humi:%5.1f%% dew point:%5.1fC\n”,temp_val.f,humi_val.f,dew_point);
}
//----------wait approx. 0.8s to avoid heating up SHTxx------------------------------
//for (i=0;i<40000;i++); //(be sure that the compiler doesn’t eliminate this line!)
delay_ms(800);
//-----------------------------------------------------------------------------------
}
}
//*************************************************************************************