I want to connect my Unity 3D Game with Micro-controller Like Arduino through Bluetooth and for that I'm using a (HC‐05) Bluetooth module.
And for that there is one plugin named Arduino Bluetooth Plugin Link in the asset Store. And Charge is 19$.
Is there any other way to do this by just using free functionality and Coding?
You can definitely do it by coding it yourself.
I can't aid you with the C# part but I've written code to send data over the HC-06 module for arduino and communicated with an Android app via bluetooth and bluetooth low energy.
At the end of the day is very similar to Socket programming.
So for the C# part this user has a basic working C# BT communication example
And for the Arduino side I have used this sketch:
With this wiring:
This image of the module may also be useful to you, so you can see the pinout:
So after pairing the arduino with my laptop and listening to incomming messages by using the command
I started seeing the output on my console:
So instead of sending a String you can send whatever you read from your Arduino inputs and then re-parse it on your C# side.
I hope I was helpful; Good luck!!!