Cool concept! I'm stuck at the 3rd puzzle, which is also one of your screenshots. It's missing some symbols, including the battery. I tried fake creating one but that didn't work either :D got any hints?
I wish it would keep the pieces you place selected so you can place multiple pieces without having to go back to the hotbar everytime. Also, I think it would be better if rotating and deleting got their own dedicated hotkey or mouse button, rather than binding everything to LMB+modifier.
I didn't get very far sadly, but I'm intrigued by the concept. Good job :D