Rosserial help

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Hello everyone, I am a beginner in ROS and have been confused very lately on how to set this up. I have 3 nodes in my current ROS setup. I want Arduino to be the 4th node and fetch/send values from these 3 nodes. But the code we upload in Arduino is .ino format ? I know there's a rosserial package in existence, but I can't figure out how to actually make it a node(which requires a cpp or py format I think).

Rosserial site says : "It allows your Arduino to be a full fledged ROS node which can directly publish and subscribe to ROS messages, publish TF transforms, and get the ROS system time."

Does that mean I simply publish and subscribe in my ino file (which need not be in my catkin_ws folder) and just upload it to arduino and run roscore+other nodes ?

Please clear the confusion! Thanks :)