Voltage Meter not working correctly

Projects Programming
24

Aref is by default internally connected to VCC of the processor,
which is about 5volt for a Mega.
You can change that by setting Aref to external, and connecting a wire between the Aref pin and the 3.3volt pin.
Warning: you must do both.
Just connecting a wire between Aref and 3.3volt will damage the processor.
The essential lines...
Leo..

void setup() {
  analogReference(EXTERNAL); // switch Aref to an external stable voltage
}

void loop() {
  float voltage = (sensor * 3.30) / 1024; // calibrate by changing the last digit(s) of 3.30.
}