Connect USB keyboard to bluetooth

I have an USB keyboard here, and I would like to connect it on bluetooth to other devices (mostly to android phones/phablets/tablets).

Yes, I know that buying a bluetooth keyboard would be more simple and cheap, but not this is what I want to do.

I know that using OTG to connect the USB device to the android directly could also work, and this is a feasible direction, but my this question focus to the other option:

I am looking for a device, where I can plug my USB keyboard into, and my androids would see it as a bluetooth device from that point.

Looking for that on the google/ebay/amazon, the search results are faded away by the reverse direction (connecting a bluetooth device over usb), or by for me irrelevant audio bluetooth transfer solutions. I simply can’t find such a device there. (Possibly I did not use the correct search keywords.)

I think such an adapter would require also a battery or/and an external (probably USB) power source.

Price is not very important yet (currently I am only looking for the options), later I will likely buy the cheapest one on the ebay.