Is the wired keyboard adapter inside or outside the wired keyboard? If it's outside, it doesn't seem to make sense because you can't make a USB cable anymore. So we will focus on how to make adapters on wired keyboards and use Mac Bluetooth on the Mac side to achieve the true meaning of Bluetooth wireless without the need for additional equipment.
How to turn a wired keyboard into a Bluetooth wired keyboard?
The Bluetooth wired keyboard is not only a communication problem, but also a power problem. I don't know if it destroys hhkb. You will see that there is no wired keyboard space to install any regular size battery. Therefore, you first need a wired keyboard to design and process a special-sized battery mounted on a wired keyboard to power the controller.
Wired keyboard Next you need a controller, the same, the first thing to solve is the small size. Wired keyboards are a good choice, and if you master basic programming, it's easy to learn.
Wired keyboard then you need a very small Bluetooth module like this or this one. Find out the basis and usage of this thing. After you know and align these things, connect them, then figure out how to play the entire system, and the first step is successful.
Next you have to find a way to install these things in a wired keyboard and connect them to HHKB's own controller. I think I will write this first. When the landlord completes the previous work, we will discuss the next approach.