A watchdog timer helps keep your embedded devices running, by making sure they are responding properly and automatically hitting reset or cycling the power if they die. I’ve added a simple hardware watchdog timer to an Arduino compatible board running inside my ceiling, where it’s difficult to access if I need to reset it manually.
Ambient information displays allow a home automation system to provide you with subtle feedback embedded within your environment. Concealing RGB LEDs behind a wall tile allows them to display status information when they are turned on, but still be totally invisible when turned off.
Connect up as many LEDs as you need, and glue them in place behind the tile. It’s best to keep the controller somewhere accessible in case you need to replace or repair it, so just have the LEDs permanently fitted behind the tile. You don’t want to have to rip out tiles and then re-tile your wall just to plug in a USB cable and update the firmware!
I’ve published an example sketch that has two separate functions: firstly it subscribes to an MQTT topic and watches for messages telling it to change the colour of an LED, and secondly it reads periodically from a DHT-22 temperature and humidity sensor and publishes the readings to other MQTT topics.