Termometer Digital Pada LM35
- Langsung dikalibrasi dalam derajat Celcius
- Linear faktor konversi 10,0 mV / º C
- Akurasi dijamin sebesar 0,5 º C (di +25 º C)
- Jangkauan kerja dari -55 º C sampai 150 º C
- Cocok untuk pengukuran jarak jauh
- Biaya Murah
- Konsumsi arus kurang dari 60 mA
- Rendahnya impedansi output, 0,1 ohm pada 1 mA beban.
Rancangan skema termometer digital saya adalah pengembangan dari termometer digital sederhana (atau lebih tepatnya, versi pada ATTiny261). Termometer digital ini menggunakan hasil modifikasi dari LM35 dengan output diferensial. Sirkuit LM35 ditunjukkan pada gambar di bawah ini :
Seperti yang dapat dilihat dari gambar, sinyal output diukur dengan voltmeter. Pada suhu nol, tegangan output dari 0.69V (dengan menggunakan BC857A transistor). Suhu di bawah nol menyebabkan penurunan tegangan output (10 mV per 1 º C).Kenaikan suhu di atas nol menyebabkan peningkatan tegangan output. Skema termometer ditunjukkan gambar dibawah ini :
Kode Program :
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#include <tiny261.h>
// Declare your global variables here
/*
*/
#include <delay.h>
#include <math.h>
#define DISP1_ON PORTA&=0xEF //PORTA&=~(1<<4)
#define DISP2_ON PORTA&=0xDF //PORTA&=~(1<<5)
#define DISP3_ON PORTA&=0xF7 //PORTA&=~(1<<3)
#define DISP4_ON PORTA&=0xFD //PORTA&=~(1<<1)
#define DISP1_OFF PORTA|=~0xEF //PORTA|=(1<<4)
#define DISP2_OFF PORTA|=~0xDF //PORTA|=(1<<5)
#define DISP3_OFF PORTA|=~0xF7 //PORTA|=(1<<3)
#define DISP4_OFF PORTA|=~0xFD //PORTA|=(1<<1)
#define A_ON PORTB&=~(1<<2)
#define B_ON PORTB&=~(1<<0)
#define C_ON PORTA&=~(1<<0)
#define D_ON PORTA&=~(1<<6)
#define E_ON PORTA&=~(1<<7)
#define F_ON PORTB&=~(1<<3)
#define G_ON PORTB&=~(1<<1)
#define DP_ON PORTA&=~(1<<2)
#define A_OFF PORTB|=(1<<2)
#define B_OFF PORTB|=(1<<0)
#define C_OFF PORTA|=(1<<0)
#define D_OFF PORTA|=(1<<6)
#define E_OFF PORTA|=(1<<7)
#define F_OFF PORTB|=(1<<3)
#define G_OFF PORTB|=(1<<1)
#define DP_OFF PORTA|=(1<<2)
#define Minus 1
#define Plus 0
#define MinusOn PORTB&=~(1<<6)
#define MinusOff PORTB|=(1<<6)
unsigned char signs;
void init_all(void);
void display_temp(unsigned int);
void display_digit(unsigned char);
unsigned int get_temp(void);
void main(void)
{
unsigned int temp;
unsigned char i;
init_all();
while(1)
{
temp=get_temp();
delay_ms(10);
display_temp(temp);
}
}
void init_all(void)
{
//set output pins
DDRA|=(1<<4);
DDRA|=(1<<5);
DDRA|=(1<<3);
DDRA|=(1<<1);
DDRB|=(1<<2);
DDRB|=(1<<0);
DDRA|=(1<<0);
DDRA|=(1<<6);
DDRA|=(1<<7);
DDRB|=(1<<3);
DDRB|=(1<<1);
DDRA|=(1<<2);
DDRB|=(1<<6);
//turn all displays OFF
DISP1_OFF;
DISP2_OFF;
DISP3_OFF;
DISP4_OFF;
A_OFF;
B_OFF;
C_OFF;
D_OFF;
E_OFF;
F_OFF;
G_OFF;
DP_OFF;
//initialize ADC
//AVCC reference select at 2.56V
ADMUX |= (1<<7);
ADMUX &= ~(1<<6);
ADCSRB |= (1<<4);
//right adjust the ADC result
ADMUX &= ~(1<<5);
//analog channel select
ADMUX &= ~(1<<4);
ADMUX |= (1<<3);
ADMUX &= ~(1<<2);
ADMUX &= ~(1<<1);
ADMUX &= ~(1<<0);
//ADC enable
ADCSRA |= (1<<7);
//ADC Stop
ADCSRA &= ~(1<<6);
//Disable free run
ADCSRB &=0xF8;
//clear ADC interrupt flag
ADCSRA |= (1<<4);
//disable ADC interrupt
ADCSRA &= ~(1<<3);
//ADC CK prescaler set to 2
ADCSRA &= ~(1<<2);
ADCSRA &= ~(1<<1);
ADCSRA &= ~(1<<0);
}
unsigned int get_temp(void)
{ int ADC_result;
int temperature;
//start ADC
ADCSRA |= (1<<6);
//wait for conversion complete
while((ADCSRA & 0b00010000) != 0b00010000)
{;}
//clear ADC interrupt flag
ADCSRA |= (1<<4);
//get result
ADC_result = ADCL + ADCH*256 ;
ADC_result= ADC_result-275;
temperature=(5* ADC_result)>>1;
if (temperature < 0)
{
temperature = abs(temperature);
signs=Minus;
}
else signs = Plus;
return ((unsigned int) temperature);
}
void display_temp( unsigned int data)
{
unsigned char hundredths, tenths, ones;
hundredths =(unsigned char)(data/100);
tenths = (data - (unsigned int)hundredths*100)/10;
ones = data - (unsigned int)hundredths*100 - (unsigned int)tenths*10;
if(signs == Minus) MinusOn;
else MinusOff;
DISP1_ON;
DISP2_OFF;
DISP3_OFF;
DISP4_OFF;
display_digit(hundredths);
delay_ms(5);
DISP1_OFF;
DISP2_ON;
DISP3_OFF;
DISP4_OFF;
display_digit(tenths);
delay_ms(5);
DISP1_OFF;
DISP2_ON;
DISP3_OFF;
DISP4_OFF;
display_digit('.');
delay_ms(5);
DISP1_OFF;
DISP2_OFF;
DISP3_ON;
DISP4_OFF;
display_digit(ones);
delay_ms(5);
DISP1_OFF;
DISP2_OFF;
DISP3_OFF;
DISP4_ON;
display_digit('C');
delay_ms(5);
}
void display_digit(unsigned char data)
{
switch(data)
{
case 0 :
{
A_ON;
B_ON;
C_ON;
D_ON;
E_ON;
F_ON;
G_OFF;
DP_OFF;
break;
}
case 1 :
{
A_OFF;
B_ON;
C_ON;
D_OFF;
E_OFF;
F_OFF;
G_OFF;
DP_OFF;
break;
}
case 2 :
{
A_ON;
B_ON;
C_OFF;
D_ON;
E_ON;
F_OFF;
G_ON;
DP_OFF;
break;
}
case 3 :
{
A_ON;
B_ON;
C_ON;
D_ON;
E_OFF;
F_OFF;
G_ON;
DP_OFF;
break;
}
case 4 :
{
A_OFF;
B_ON;
C_ON;
D_OFF;
E_OFF;
F_ON;
G_ON;
DP_OFF;
break;
}
case 5 :
{
A_ON;
B_OFF;
C_ON;
D_ON;
E_OFF;
F_ON;
G_ON;
DP_OFF;
break;
}
case 6 :
{
A_ON;
B_OFF;
C_ON;
D_ON;
E_ON;
F_ON;
G_ON;
DP_OFF;
break;
}
case 7 :
{
A_ON;
B_ON;
C_ON;
D_OFF;
E_OFF;
F_OFF;
G_OFF;
DP_OFF;
break;
}
case 8 :
{
A_ON;
B_ON;
C_ON;
D_ON;
E_ON;
F_ON;
G_ON;
DP_OFF;
break;
}
case 9 :
{
A_ON;
B_ON;
C_ON;
D_ON;
E_OFF;
F_ON;
G_ON;
DP_OFF;
break;
}
case '.' :
{
DP_ON;
break;
}
case 'C' :
{
A_ON;
B_ON;
C_ON;
D_ON;
E_OFF;
F_OFF;
G_OFF;
DP_ON;
break;
}
default: break;
}
}
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