#define F_CPU 8000000UL
#include <avr/io.h>
#include <util/delay.h>
#include <stdlib.h>
 
void USART_Init(unsigned int ubrr) {
    UBRRH = (unsigned char)(ubrr >> 8);
    UBRRL = (unsigned char)ubrr;
    UCSRB = (1 << RXEN) | (1 << TXEN);
    UCSRC = (1 << URSEL) | (1 << UCSZ1) | (1 << UCSZ0);
}
 
void USART_Transmit(unsigned char data) {
    while (!(UCSRA & (1 << UDRE)));
    UDR = data;
}
 
unsigned char USART_Receive(void) {
    while (!(UCSRA & (1 << RXC)));
    return UDR;
}
 
void USART_SendString(const char* s) {
    while (*s) USART_Transmit(*s++);
}
 
void ADC_Init(void) {
    ADMUX = (1 << REFS0);
    ADCSRA = (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0);
}
 
uint16_t ADC_Read(void) {
    ADCSRA |= (1 << ADSC);
    while (ADCSRA & (1 << ADSC));
    return ADC;
}
 
int main(void) {
    char buffer[20];
    uint16_t adc_value;
    uint32_t millivolts;
 
    USART_Init(51);
    ADC_Init();
 
    while (1) {
        if (USART_Receive() == '*') {
            adc_value = ADC_Read();
            millivolts = (adc_value * 5000UL) / 1024;
            itoa(millivolts, buffer, 10);
            USART_SendString("Voltage=");
            USART_SendString(buffer);
            USART_SendString("mV\r\n");
        }
    }
}

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