Temperature sensor LM75

[ibg]

Hi,

I have been reading the datasheet for the temperature sensor LM75 and is said that the temperature value is represented by 9 bits in 2 complement.

If I read two bytes in order to read such value, do I have to program some special case in order to know if the temperature is negative or positive?

[godinel claudiu]

Ok... guys now here is the program that reds more temperature sensors lm75 -cim5 connected to a i2c 2 wire bus.
all you need to do is ad if and Lm75_wite_n and lm75_read_n and change tehe last if....hope you like it..

I will try to make a dallas 1 wire bus now, and make it so send data to the rs232 to output it nice in some plots...
But first i must get some ds1820 or ds18s20 or ds18b20 , and i only found ds18s20+, does anyone know the difference ?


#include <16F870.h>
#use delay(clock=4000000)
#fuses XT,NOWDT,PUT,NOPROTECT,BROWNOUT,NOLVP,NOCPD,NOWRT,NODEBUG
#define SDA_PIN PIN_C2 // i2c serial data in/out
#define SCL_PIN PIN_C3 // i2c serial clock
#define p1 PIN_A3
#define LM75_WRITE1 0x90 // 1001 0000
#define LM75_READ1 0x91 // 1001 0001
#define LM75_WRITE2 0x9e // 1001 1110
#define LM75_READ2 0x9f // 1001 1111

#use i2c(master,sda=SDA_PIN, scl=SCL_PIN)
int8 dataH,dataL,temp,senz,x;
int1 flgSign;
char grad;

void i2c_init(void)
{
output_high( SCL_PIN );
output_high( SDA_PIN );
}


void lm75_start(int8 x)
{
i2c_start();
if (x==1) i2c_write(LM75_WRITE1);
else i2c_write(LM75_WRITE2);
i2c_write(0x01); // Pointer Byte
i2c_write(0x00); // Configuration Byte (operating)
i2c_stop();
}

void lm75_setandread(int8 x)
{
i2c_start();
if (x==1) i2c_write(LM75_WRITE1);
else i2c_write(LM75_WRITE2);
i2c_write(0x00); // Pointer Byte
i2c_start();
if (x==1) i2c_write(LM75_READ1);
else i2c_write(LM75_READ2);
dataH = i2c_read(); // with ACK
dataL = i2c_read(0); // with NOACK
i2c_stop();
}

#include <lcdme.c>

main() {

i2c_init();
delay_ms( 10 );
lcd_init();
senz=1;
grad=223;

while(1)
{

lcd_gotoxy(1,1);
printf(lcd_putc,"Senz");
lcd_gotoxy(6,1);
printf(lcd_putc,"%u =",senz);

lm75_start(senz);
delay_ms( 30 );
lm75_setandread(senz);
//lm75_shutdown();
delay_ms( 100 );

// Stabileste valoarea/semnul temperaturii (in 0,5 grade Celsius)
flgSign = 0;
if( bit_test( dataH, 7 ) ){ // semn negativ (bit-ul 7 setat)
flgSign = 1;
dataH = ( 0xFF - dataH + 1 );
}
dataH = ( dataH << 1 );
if( bit_test( dataL, 7 ) ) // 0,5 grade (bit-ul 7 setat)
dataH |= 0x01;

// Ajusteaza valoarea temperaturii (cu +2 grade) (4 unitati de 0,5 grade)
if (senz==1) dataH -= 25 ;
if (senz==2) dataH -= 33 ;
dataL += 128 ;
temp=dataH;

lcd_gotoxy(1,2);
printf(lcd_putc,"Tmp");
lcd_gotoxy(5,2);
printf(lcd_putc,"%u" ,dataH);
lcd_gotoxy(7,2);
printf(lcd_putc,"%cC",grad);
if (!input(p1)) {senz=senz+1; if(senz==3) senz=1;}
delay_ms(100);
}}
// made by Godinel Claudiu
// made by Godinel Claudiu
// made by Godinel Claudiu
//mess id claudiu_godinel for further questions

[Humberto]

[godinel claudiu]

hei..Thanks... did'nt know allu sad about them...

But does someone know someting about ds18s20+ ?

I would like to mention that
Ds18b20 is compatible with ds1822 & and can be user on 9 or 12 bits of rezolution.

And Ds18s20 is compatible whit Ds1820 and have 9 bits of rezolution.

[Humberto]