A little question for the HA and DIY crossroad. Has anyone here made your own sensors/devices with arduino, pi or some other microcontroller/sbc to interact with HA? I have some spare parts around and I'm thinking in something simple, like an air quality, maybe a little weather station or something to tell me if the garage door is opened or close, something simple, yet usable. I had a look on instructables, but I wished for something that would integrate with my first HA experience. Any thoughts?

Edit: thanks everyone for the replies. If you could share how-tos to this projects or anything it would be awesome. You are a great community indeed! :)