This is great IoT hardware built for industrial and home automation purposes.
It has 4 Relay outputs and 4 inputs. All inputs and outputs are isolated by optocouplers and you'll need external 12V (besides 5V supply for the MCU) for powering the relays. As it is in the description, this is done mainly for industrial purposes and reliability, that is the reason for separate power supplies for the MCU and the relays.
This product is designed by our team and at this moment it is in use by controlling and monitoring remote water pump.
You can find all documents and source files for this design attached on this post.
Enjoy building it!