#define RELAIS_12V 11

int adc_12v_old = 0;
int adc_12v = 0;
int adc_12v_upper_limit = 647;  // 15V
int adc_12v_lower_limit = 474;  // 11V
int ADC_12V = 0;

void setup(void){
    pinMode(RELAIS_12V, OUTPUT);
}

void checkADC(void){
    adc_12v = analogRead(ADC_12V);
      if ((adc_12v > adc_12v_upper_limit) || (adc_12v < adc_12v_lower_limit)){
        digitalWrite(RELAIS_12V, LOW);
  }
  else{
      digitalWrite(RELAIS_12V, HIGH);
  }
}

void loop(){
 checkADC();
 delay(30);
}