This is really cool, looks like it will make integrating your microcontroller with other systems really easy.

But - and I hate to be the REST Nazi - this is RPC, not REST.

"REpresentational State Transfer" is about making things happen by Transferring REpresentations of resources' State.

The GET requests are good, but for setting outputs it should do something like:

  PUT http://192.168.1.177/9
  

with body

  HIGH

POST could work too, the important thing is that the resource's state, the resource's address, and the action being performed are all separate.

This RPC system is beautifully simple, it does what it needs to and I can't think of any way that making it RESTful would improve it, but it's not RESTful right now, and calling it that only deepens the confusion about what REST is.