We'll set up the foundation of a Home Automation System with:
- A single Arduino with a temperature sensor,
- Which sends the data wirelessly to a Raspberry Pi,
- Which will fetch the message,
- Publish it to an MQTT channel,
- Where the OpenHAB MQTT binding will pick it up,
- So it can be displayed in a web browser (and used for rules).
If this sounds complicated, don't worry. We'll go through it step by step and explain everything along the way.
If this sounds too easy, don't worry. This is just the foundation for a system you can make as simple or as complicated as you desire.
Once you have this basic scenario working, expanding it will be easy.
The initial hardware cost (Pi starter kit + Arduino + RF24 modules + wires + sensor) will be less than $100.
The software cost is $0, because we'll only use free & open source software.
Expanding on this project is possible for very little cost: you can add more sensors to the Arduino for a few dollars each, and each additional Arduino + RF24 should cost about $20.
You can find the components at many electronics stores, though you often get the best prices online like from 3rd party vendors on Amazon.com.
Product links to Amazon.com, with the price at the time of writing:
You can also use a Raspberry Pi B instead of B+, and an Arduino Nano instead of Uno.
Pictured below is a SainSmart Arduino Nano + USB cable ($14.80) on a breadboard with plenty of room for sensors and a breadboard power supply ($5.99) so you can power it when not connected to your computer's USB port.