Using 1.1Vf to read stable battery voltage and sensor voltage

Question

After several tries, i was successful with reading stable battery voltage using internal voltage reference of 1.1v, now the issue i face is that i cannot read stable sensor voltage, could you please let me know how can i read my sensor voltage? or do i need additional voltage divider (my sensor goes directly to A0 and GND pin).

  void setup(){
  Serial.begin(9600);
}

void loop() {  
  //REFS1 AND REFS0 to 1 1 -> internal 1.1V refference
  ADMUX |= B11000000;   
  //We read A1 (MUX0) for battery voltage
  ADMUX |= B00000001;       
    //We read A0 for sensor voltage
  ADMUX |= B00000000;                // for my sensor 
  // Start AD conversion
  ADCSRA |= B11000000;
  // Detect end-of-conversion
  while (bit_is_set(ADCSRA,ADSC));
  float val = ADCL | (ADCH << 8);
  val = val * 5.7; // Using 4.7k and 1k voltage divider
  Serial.println(val);
}

Something like the code below must workout but unfortunately it does not help!

  int sensorValue = analogRead(A0);
  voltage =  ((sensorValue/ val) * 1023.); 
  delay(1000);
  Serial.println("voltage:  ");
  Serial.print(voltage); 
  if (voltage<=215){
  digitalWrite (led, HIGH);
  }
  else if (voltage>=215){
  digitalWrite (led, LOW);
  }

I cannot find the issue, it should work, i believe.

//////////////////////new edit/////////////////////////////////////

const long internalReference = 1078L; //measured AREF to be 1.078 ~ 1.078*1000= 1078V

void setup() {
  // put your setup code here, to run once:
Serial.begin (115200);
}

void loop() {
 analogReference (INTERNAL);
 ADMUX |= B00000000;
 ADCSRA |= B11000000;    //ADEN and ADSC equal to 1   (Start conversion)
  while(bit_is_set(ADCSRA, ADSC));    //Wait for conversion to end
  long val = ADCL | (ADCH << 8);   //Get analog read value  
  float voltage = (val/internalReference)*1024;
 Serial.println (voltage);
 
 }

Answer 1

To measure the voltage at A0 with an internal reference of 1.1v, the formula is float voltage = 1.1 * analogRed(A0) / 1023;. Your code can be simplified as

float Vref = 1.1;

void setup(){
  Serial.begin(9600);
}

void loop() {
  analogReference (INTERNAL);
  float voltage = Vref * analogRead(A0) / 1023;
  Serial.print (“voltage at A0:”);
  Serial.println(voltage);
  Serial.print (“Solar panel voltage:”);
  Serial.println(voltage * 5.7);
  delay(1000);
}