   // check all lines for incoming data
   for (int i=0;i<NUM_CONN;i++) if(bus[i]->available()) {
     char c = bus[i]->read();
-    if(SERIAL_DEBUG) Serial.println("received: "+c);
+    if(SERIAL_DEBUG) {
+      Serial.print(i);
+      Serial.print(": ");
+      Serial.println(int(c));
+    }
     switch(c) {
       case ALERT: // button is pressed
         if (!isSource && !alertState) {

  if(SERIAL_DEBUG) {
    Serial.begin(9600);
    Serial.println("setup");
  }
}


  // assess energy supply, find shortest disance to source
  shortestDistanceToSource = 99;
  for (int i =0; i<NUM_CONN; i++) if (distanceToSource[i] < shortestDistanceToSource) shortestDistanceToSource = distanceToSource[i];

  if(SERIAL_DEBUG) {
    Serial.print("sd: ");
    Serial.println(shortestDistanceToSource);
  }

  // if we have energy, switch (or keep) lamp on, pass it on and check again in some time
  if (shortestDistanceToSource<99) {
