Electrical – How to read LM34 temperature sensor negative voltage with an ATmega32

I'm trying to read the temperature with an LM34 but it only reads from 0 to 50 F. Its range is from -50 to +300 F. I asked a lot and I found that my circuit below can't read a negative voltage:

What should I do to read negative voltages?

I also found that because I use single pin to read the temperature this makes me only measure a couple degrees not all the degrees. What should I do to read all of the degrees and what would the code be?

My code:

#include <util/delay.h>
#include <stdio.h>
#include <avr/io.h>


// define port C
#define LCD_DDDR   DDRC   /*LCD DATA DDR*/              
#define LCD_DPRT   PORTC   /*LCD DATA PORT*/             
#define LCD_DPIN   PINC   /*LCD DATA PIN*/               
// define port D
#define LCD_CDDR  DDRD   /*LCD COMMAND DDR*/            
#define LCD_CPRT  PORTD    /*LCD COMMAND PORT*/           
#define LCD_CPIN  PIND    /*LCD COMMAND PIN*/            

#define LCD_RS 0      //LCD RS
#define LCD_RW 1      //LCD RW
#define LCD_EN 2      //LCD EN

void delay_us(unsigned int d)
{
    while(d) {
        _delay_us(1);
        d--;
    }
}

void lcdCommand(unsigned char cmnd)
{
    LCD_DPRT = cmnd;                //send cmnd to data port
    LCD_CPRT &= ~(1<<LCD_RS);       //RS = 0 for command
    LCD_CPRT &= ~(1<<LCD_RW);       //RW = 0 for write
    LCD_CPRT |= (1<<LCD_EN);        //EN = 1 for H-to-L pulse
    delay_us(1);                    //wait to make enable wide
    LCD_CPRT &= ~(1<<LCD_EN);       //EN = 0 for H-to-T pulse
    delay_us(100);                  //wait to make enable wide
}

void lcdData(unsigned char data)
{
    LCD_DPRT = data;                //send data to data port
    LCD_CPRT |= (1<<LCD_RS);        //RS = 1 for data
    LCD_CPRT &= ~(1<<LCD_RW);       //RW = 0 for write
    LCD_CPRT |= (1<<LCD_EN);        //EN = 1 for H-to-L pulse
    delay_us(1);                    //wait to make enable wide
    LCD_CPRT &= ~(1<<LCD_EN);       //EN = 0 for H-to-l pulse
    delay_us(100);                  //wait to make enable wide
}

void lcd_init()
{
    LCD_DDDR = 0xff;                //all pins in port C output
    LCD_CDDR = 0xff;                //all pins in port D output

    LCD_CPRT &= ~(1<<LCD_EN);       //LCD_EN = 0
    delay_us(2000);                 //wait for init
    lcdCommand(0x38);               //init. lcd 2 line, 5 x 7 matrix
    lcdCommand(0x0e);               //display on, cursor on
    lcdCommand(0x01);               //clear LCD
    delay_us(2000);                 //wait
    lcdCommand(0x06);               //shift cursor right
}

void lcd_gotoxy(unsigned char x, unsigned char y)
{
    unsigned char firstCharAdr[] = {0x80, 0xc0, 0x94, 0xd4};
    lcdCommand(firstCharAdr[y - 1] + x - 1);
    delay_us(100);
}

void lcd_print(char* str)
{
    while (*str)
    {
        lcdData(*str++);
    }
}

int main(void)
{

    char buffer[3];

    DDRA |= 0b00000111;             //pin 0,1,2 output & pin 3,4,5,6,7 input.
    DDRB |= 0xFF;                   // make port B output.
    ADCSRA |= 0x87;                 //make ADC enable and select ck/128.
    ADMUX |= 0xE6;                  //2.56 v vref, select ADC6 and make left justified.

    lcd_init();
    lcd_gotoxy(1, 1);
    lcd_print("temperature:");

    while(1)
    {
        ADCSRA |= (1 << ADSC);                               //start conversion

        while (ADCSRA & (1 << ADSC));
        PORTB = ADCH;

        if (ADCSRA&0b00000101)
        {
            sprintf(buffer, "%d", PORTB);
            lcd_gotoxy(1, 2);
            lcd_print(buffer);
        }
    }
    return 0;
}