As spotted on Reddit, Robson Couto was in need of a USB to MIDI adapter, and decided to pursue the “easiest USB MIDI implementation [he] could build in an afternoon.” Fortunately, Yoshitaka Kuwata had a similar idea, and Couto decided to modify his implementation to run on a USBasp AVR programmer, normally used to program AVR microcontrollers found on many Arduino boards. Since they are small and only cost a couple bucks, Couto keeps several on-hand.
For his adapter implementation, code (available here) was burned into the designated programmer using another USBasp module. The MIDI cable is hooked up to the programmer via a simple custom board and header, with a 6N138 opto-isolator separating the USBasp and MIDI signals. The boards use header pins for attachment, so if for some reason it needs to be converted back to a programmer, it should be a matter of unplugging and reprogramming.
This isn’t Couto’s first foray into re-purposing these programmers; he was actually able to use one of these as a Super Nintendo controller interface with another custom adapter in a previous project. While these devices certainly work well for programming chips as intended, perhaps it’s worth having a few around for custom USB adapter projects as well!