+ /*
+ * have serial packet?
+ *
+ * decode msg & process:
+ * - dispense motor
+ * - display string
+ * - give change
+ * - beep
+ */
+
+ /*
+ * have keypress?
+ * - beep
+ * - send via serial
+ */
+
+ /*
+ * have coin balance change?
+ * - send via serial
+ */