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pictrance
Joined: 18 Jul 2010
Posts: 14
Location: Puebla, Mexico
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| Driver for SHT21 |
 Posted: Tue Jun 28, 2011 2:52 pm |
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hi!
I want to share with you the driver for the sht21 (temperature and humidity sensor)
and the code is:
| Code: | ////////////////////////////////////////////////////////////////////////////////
/// sht21.c ///
/// Driver for temperature and humidity sensor ///
/// Realizado por PicTrance ///
/// junio del 2011, Puebla - México ///
/// Compiler: CCS ///
/// ///
/// sht21_init() - Iicializa el sensor sht21 - ///
/// ///
/// ///
/// sht21_temp(temperatura) Get the temperature, lee tempeartura ///
/// ///
/// sht21_humid(humedad) Get the humidity, lee humedad ///
/// ///
/// sht21_both(temp,humd) Get the temperature and humidity ///
/// Lee temperatura y humedad ///
////////////////////////////////////////////////////////////////////////////////
#define sht21 0b10000000
#define writeuser 0b11100110
#define readuser 0b11100111
#define reset 0b11111110
#define temphold 0b11100011
#define humidhold 0b11100101
#define read 0b10000001
#define softreset 0b11111110
/*int8 msbhum, lsbhum, msbtemp, lsbtemp, checksum;
int16 temperies, humidum;
float temperiess, humidumm;*/
int8 checksum;
void sht21_init(void){
i2c_start();
i2c_write(sht21);
i2c_write(softreset);
i2c_stop();
delay_ms(15);
}
void SoftResett(){
i2c_start();
i2c_write(sht21);
i2c_write(softreset);
i2c_stop();
delay_ms(15);
}
void sht21_temp(float &temperies1){
//float temperies1;
int8 msbtemp, lsbtemp;
int16 temperies;
float temperiess;
i2c_start();
i2c_write(sht21);
i2c_write(temphold);
i2c_start();
i2c_write(read);
msbtemp = i2c_read();
lsbtemp = i2c_read();
checksum = i2c_read();
//i2c_read(0);
i2c_stop();
temperies = make16(msbtemp,lsbtemp);//valiable = MAKE16(varhigh, varlow) junta las
//2 variables in8 en una in16
/*#ASM
movf lsbtemp,0
movwf 0x00A
movf msbtemp,0
movwf 0x00B
#ENDASM*/
temperiess=temperies;
temperies1= (-46.85 + (175.72*(temperiess/65536)));
SoftResett();
//return temperies1;
}
void sht21_humid(float &humidum1){
//float humidum1;
int8 msbhum, lsbhum;
int16 humidum;
float humidumm;
i2c_start();
i2c_write(sht21);
i2c_write(humidhold);
i2c_start();
i2c_write(read);
//delay_ms(25);
msbhum = i2c_read();
lsbhum = i2c_read();
checksum = i2c_read();
//i2c_read(0);
i2c_stop();
humidum = make16(msbhum,lsbhum);
/*#ASM
movf lsbhum,0
movwf 0x00C
movf msbhum,0
movwf 0x00D
#ENDASM*/
humidumm=humidum;
humidum1= (-6 + (125*(humidumm/65536)));
SoftResett();
//return humidum1;
}
void sht21_both(float &tmp, float &humd){
/*float temp;
float humedad;*/
sht21_temp(tmp);
delay_us(800);
sht21_humid(humd);
} |
an example of how to use:
| Code: | ///Ejemplo de como usar el driver
///sht21.c, creado por PicTrance
///para el foro de Neoteo y el foro de CCS
///funciona para el compilador CCS
#include <18f4550.h>
#device adc=10
#fuses HS,NOWDT,NOPROTECT,NOLVP,NODEBUG
#use delay(clock=20M)
//Pal bootloader
#build (reset=0x1000,interrupt=0x1008)
#org 0x0000,0x0FFF{}
//#use i2c(Master,fast,sda=PIN_C7,scl=PIN_C6)
#use i2c(Master,fast,sda=PIN_A4,scl=PIN_A5)
//#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7)
#include "lcd4x20.c"
#include "sht21.c"
int signo = 0xDF;//simbolo "°"
void main(){
float tempi,humedadi;
SETUP_ADC(ADC_OFF);
lcd_init();
set_tris_b(0x00);
set_tris_c(0b00000000);
lcd_putc("\fSensor de \nTemperatura y\nHumedad SHT21");
delay_ms(500);
output_c(0b11111000);
sht21_init();
delay_ms(300);
while(true){
sht21_temp(tempi);
delay_ms(100);
sht21_humid(humedadi);
//sht21_both(tempi,humedadi);
printf(lcd_putc, "\fTemp: %f %cC",tempi, signo);
printf(lcd_putc, "\nRH: %f %%",humedadi);
delay_ms(1000);
}
} |
I hope that this driver helps someone
_________________
Si el proyecto tiene mal olor es de Química, Si echa humo negro es de Mecánica, Si es verde o se retuerce es de Bioingenieria Y si no funciona es de Electrónica.. :p ... no es mia la frase, pero me gusto. |
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Pichuqy_1
Joined: 03 Aug 2010
Posts: 38
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| Posted: Tue Jul 28, 2015 8:46 pm |
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| I tried and not worked. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Jul 29, 2015 3:14 pm |
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Here's the SHT21 data sheet:
http://www.sensirion.com/fileadmin/user_upload/customers/sensirion/Dokumente/Humidity/Sensirion_Humidity_SHT21_Datasheet_V4.pdf
Look at the i2c protocol bit diagrams on page 8. Notice how they read the
data (msb), data (lsb), and checksum bytes, and then the PIC issues a
NACK. In his code below, he doesn't do the NACK. This is a violation of
the SHT21 data sheet. If you skip the NACK on the last read, I know for
a fact that you will get bad data on subsequent reads on many i2c chips.
I have seen this happen while testing i2c eeprom chips to study the effect
of a missing NACK.
| Quote: |
i2c_write(read);
msbtemp = i2c_read();
lsbtemp = i2c_read();
checksum = i2c_read();
//i2c_read(0);
i2c_stop(); |
The line in bold should be:
| Code: | | checksum = i2c_read(0); |
He has this mistake in these routines:
sht21_temp()
sht21_humid() |
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