//https://batteryglobe.com/car-battery-voltage-chart/
//https://www.kwik-fit.com/blog/what-voltage-should-a-car-battery-be#
//https://ecosoch.com/lead-acid-battery/

uint8_t ledState = 0;
int correction = 19;

void setup() {
  Serial.begin(115200);
  pinMode(10, OUTPUT);
  pinMode(A0, INPUT);
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(10, LOW);
}

void loop() {
  if (((analogRead(A0) >= (959 + correction)) && (analogRead(A0) < (975 + correction))) && (ledState != 2)) { // > 11.99V and < 12.2
    digitalWrite(10, HIGH);
    ledState = 1;
  } else if (analogRead(A0) < (959 + correction)) { // < 11.99V (from 56k/36k divider 4.69V)
    digitalWrite(10, LOW);
    ledState = 2;
  } else if (analogRead(A0) > (981 + correction)) { // > 12.3V (from 56k/36k divider 4.74)
    digitalWrite(10, HIGH);
    ledState = 0;
  }


  // LED off: 0 -- battery ok
  // LED on: 1 -- battery is going low, prepare for charge
  // LED blink: 2 -- battery discharged, charge asap
  if (ledState == 2) {
    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
  } else if (ledState == 0) {
    digitalWrite(LED_BUILTIN, LOW);
  } else if (ledState == 1) {
    digitalWrite(LED_BUILTIN, HIGH);
  }

  delay(1000);
  Serial.println(analogRead(A0));
}