const int DO_PIN = A0;

void setup() {
  Serial.begin(115200);
  pinMode(DO_PIN, INPUT);
}

void loop() {
  int raw = analogRead(DO_PIN);
  float voltage = raw * 5.0f / 1023.0f;
  Serial.print("raw=");
  Serial.print(raw);
  Serial.print(", voltage=");
  Serial.println(voltage, 3);
  delay(1000);
}