Added mqtt status message for output pins; moved output init to beginning of setup

README.md

@@ -3,11 +3,34 @@
 Based on
 
 - Arduino Uno
-- Ethernet interface
+- Ethernet interface using MQTT
 
 Watchout for GPIO changes as triggers for
 
 - door bell input
-- post box observer (post entry)
-- post box observer (takeout posts)
-- ...
+- mailbox observer (post entry)
+- mailbox observer (takeout posts)
+- light requests (button)
+
+Serve outputs (using relays to trigger) for
+
+- turn light on at mailbox
+- turn bell sound on
+
+MQTT messages:
+
+- doorBellTopic = "doorBellGW/doorbell"
+  --> issued when pushbutton pressed: trigger / re-trigger / release
+- postboxFlapTopic = "doorBellGW/mailboxFlap"
+  --> issued, when flap is opened to enter mail: trigger / re-trigger / release
+- postboxDoorTopic = "doorBellGW/mailboxDoor"
+  --> issued, when mailbox door is opened to remove mail: trigger / re-trigger / release
+- doorBellTriggerSoundTopic = "doorBellGW/doorbellTrigger"
+  --> listens to this message and turns on relay for a short time to trigger the bell/gong
+- doorLightRequestTopic = "doorBellGW/lightRequest"
+  --> issued, when light pushbutton is pressed: trigger / re-trigger / release; light is turned on for 30 seconds
+- postboxLightTopic = "doorBellGW/light"
+  --> listens to this message and turns light on at mailbox for 30 seconds
+- postboxLightStatusTopic = "doorBellGW/light/status"
+  --> issued, when light at mailbox is turned on/off: on / off
+