Temperature Sensor

#include <avr/io.h>
#include <util/delay.h>
#include <avr/sleep.h>
#include <avr/interrupt.h>
#include <util/atomic.h>

void flash(void);
inline void LED(uint8_t on);
void Error(uint8_t);
uint8_t getTemp(void);
void sendRS232Byte(uint8_t);

//RS232 defines
#define BAUD 9600
#define RS232_PAUSE 1000000/BAUD

volatile uint16_t timeroverflow;


int main(void){
    //ADC init
    ADMUX=(1<<REFS1)|(1<<MUX3)|(1<<MUX2)|(1<<MUX1)|(1<<MUX0);
    ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0); //ADC Freq: ~63khz
    ADCSRB=0;
    getTemp(); //init

    DDRB=(1<<PB4)|(1<<PB1); //Enable LED output, SDA, SCL
    PORTB|=(1<<PB1);    //PB1 high

    //Timer init
    TCCR1=0xF;  //Timer/16384 -> overflow ~0,5s
    GTCCR=0;
    TIMSK=(1<<TOIE1);



    LED(1);             //Start
    _delay_ms(1000);
    LED(0);

    timeroverflow=0;

    sei();
    uint16_t temp;
    while(1){
        ATOMIC_BLOCK(ATOMIC_RESTORESTATE){
            temp=timeroverflow;
            if(temp>12){            //~10min
                timeroverflow=0;

                sendRS232Byte(getTemp());
                flash();
            }
        }
    }

    return 0;
}


uint8_t getTemp(void){
    ADCSRA|=(1<<ADSC)|(1<<ADIF);
    while(ADCSRA&(1<<ADSC));
    return (ADC>>2);
}

inline void LED(uint8_t on){
    switch (on){
        case 0:
            PORTB&=~(1<<PB4);
            break;
        default:
            PORTB|=(1<<PB4);
        }
}


void flash(){
    LED(1);
    _delay_us(50);
    LED(0);
}

void sendRS232Byte(uint8_t data){
    DDRB|=(1<<PB1);
    PORTB|=(1<<PB1);                    //Idle
    _delay_us(10*RS232_PAUSE);
    PORTB&=~(1<<PB1);                   //Start-Bit
    for(uint8_t i=0;i<8;i++){   //8 Bits
        _delay_us(RS232_PAUSE);
        switch((data>>i)&1){
            case 1:
                PORTB|=(1<<PB1);
                break;
            case 0:
                PORTB&=~(1<<PB1);
                break;
        }
    }
    _delay_us(RS232_PAUSE);
    PORTB|=(1<<PB1);                    //Stop-Bit
    _delay_us(10*RS232_PAUSE);
}

ISR(TIMER1_OVF_vect){
    timeroverflow++;
}