Keurig/Arduino Coffee Maker

#include <avr/eeprom.h>

void setup()
{
  analogReference(EXTERNAL);

  pinMode(A0, INPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
}

uint16_t readUserTemp()
{
  return eeprom_read_word(0);
}

void writeUserTemp(uint16_t v)
{
  eeprom_write_word(0, v);
}

boolean user_heater_on = false;
uint32_t last_button = 0;
uint32_t last_relay_engage = 0;
boolean debounce = false;

void loop()
{
  boolean bt_on = !digitalRead(2);
  boolean bt_down = !digitalRead(3);
  boolean bt_up = !digitalRead(4);
  boolean bt_pump = !digitalRead(5);

  if (debounce && !(bt_on | bt_down | bt_up | bt_pump))
    debounce = false;

  if (!debounce &&
      millis() - last_button > 250 &&
      (bt_on | bt_down | bt_up | bt_pump))
  {
    debounce = true;
    last_button = millis();
    if (bt_on)
      user_heater_on = !user_heater_on;
    else if (bt_down)
      writeUserTemp(readUserTemp() - 1);
    else if (bt_up)
      writeUserTemp(readUserTemp() + 1);
  }

  uint16_t ntc = analogRead(A0);
  Serial.print("A0 = ");
  Serial.print(ntc);
  Serial.print(", USER = ");
  Serial.println(readUserTemp());

  if (ntc > readUserTemp() && millis() - last_relay_engage > 1000)
  {
    Serial.println("ABOVE USER TEMP, HEAT OFF");
    digitalWrite(12, LOW);
    last_relay_engage = millis();
  }
  else if (user_heater_on && ntc < readUserTemp() && millis() - last_relay_engage > 3000)
  {
    Serial.println("HEAT ON");
    digitalWrite(12, HIGH);
    last_relay_engage = millis();
  }
  else if (!user_heater_on)
  {
    digitalWrite(12, LOW);
  }

  Serial.print("Time: ");
  Serial.print(millis());
  Serial.print(", last relay: ");
  Serial.println(last_relay_engage);

  // LED blinks
  if (user_heater_on)
  {
    if (ntc > readUserTemp())
      digitalWrite(13, (millis() / 50) % 10 > 0);
    else
      digitalWrite(13, HIGH);
  }
  else
  {
    if (ntc > readUserTemp())
      digitalWrite(13, (millis() / 50) % 10 == 0);
    else
      digitalWrite(13, LOW);
  }

  if (bt_pump)
  {
    user_heater_on = false;
    analogWrite(11, 96);
  }
  else
    analogWrite(11, 0);

  delay(50);
}