volatile uint16_t TMP36_VoutADCReading = 0U;

void TMP36_Init( void )
{
   // Set the ADC prescaler to 128 (i.e., 16MHz/128 = 250kHz)
   ADCSRA |= ( 1 << ADPS2 ) | ( 1 << ADPS1 ) | ( 1 << ADPS0 );

   // Set the voltage reference from AVcc (i.e., 5V).
   // ADMUX |= ( 1 << REFS0 );

   // Turn on the ADC.
   ADCSRA |= ( 1 << ADEN );

   // Do the initial conversion (i.e., the slowest conversion)
   // to ensure that everything is up and running.
   ADCSRA |= ( 1 << ADSC );
}

void TMP36_ADCRead( uint8_t channel )
{
   // Clear the previously read channel.
   ADCSRA &= 0xf0;

   // Select the ADC channel to be read.
   ADMUX |= channel;

   // Start a new conversion. By default, this conversion will
   // be performed in single conversion mode.
   ADCSRA |= ( 1 << ADSC );

   // Wait until the conversion is complete.
   while( ADCSRA & ( 1 << ADSC ) );

   // Obtain the ADC reading from Vout.
   TMP36_VoutADCReading = ADC;
}

int main( void )
{
   // Disable all interrupts for the time being.
   cli();

   // Initialize the TMP36GZ temperature sensor.
   TMP36_Init();

   // Enable all interrupts.
   sei();

   while( 1 )
   {
      // Compute the distance.
      uint8_t channel = 1;
      TMP36_ADCRead( channel ); // At this point, TMP36_VoutADCReading = 1023
   }
}