   pinMode(upButton, INPUT_PULLDOWN);
   debounceDown.begin();
   debounceUp.begin();
+
+  nvic_globalirq_disable();
+  displayNumber(0xF);
+  delay(3000);
   
 #ifdef SERIAL_DEBUG
   Serial.begin(115200);

const uint32_t watchdogSeconds = 10;
const uint32_t numInjectionModes = sizeof(injectors)/sizeof(*injectors);

const uint32_t indicatorLEDs[] = { PA0, PA1, PA2, PA3 };
const int numIndicators = sizeof(indicatorLEDs)/sizeof(*indicatorLEDs);
const uint32_t downButton = PA4;


void displayNumber(uint8_t x) {
  for (int i=0; i<numIndicators; i++, x>>=1) 
    analogWrite(indicatorLEDs[i], (x&1) ? (255-ledBrightnessLevels[i]) : 255);
}

void updateDisplay() {
