One of the simplest things you can do is hook up a DHT11 to an ESP and get a remote temperature reading. The fact it includes humidity too is a bonus, most people don’t go looking for humidity sensors nearly as much as temperature sensors. The DHT11 is fine and all, but I happened to have a DHT22 handy. The differences are minor, but the code needs to be updated. There is a library to use these sensors with and it is quite handy as well as the example code calling out how the settings need to be changed in the comments.
My implementation has 2 MQTT calls, one for the temperature and one for the humidity. I added a second output line to each that sends a message to the LED sign for display (although it’s easy enough to amend what topics these are listening on and what they send to). Now when you ask for temperature or humidity you get the response to inTopic, but also it gets displayed on the sign. You could have an architecture where the temp sensor is listening on a topic and the humidity is listening on another and when either get a message they interpert that as a command to send their reading out, but they pick the channel based on the message you send them. You can also have delimiters and parse the commands pretty easily from one topic. There are so many ways to implement MQTT it’s both fantastic and terrible. You can do it however works best for you, but anyone else’s system will need adapting to work with yours.
As should be expected the code is here.
The rest of this series can be gotten through from the home page here.