I picked this up from Reverb or eBay or somewhere years ago—I guess the/a previous owner stripped down an NFVM1 and started to saw off the upper horn, and then, presumably, abandoned that approach in favor of sanding the horn into a rounded edge and, of course, sanded everything else. Yikes! 
This is still a work in progress, but my students and I have been using Sprocket as a "guitar breadboard" of sorts for some electronics projects we're developing, but, now, I think we're committing to a dedicated set of electronics, so...
Our electronics in the cavity is part of project we've been cooking up for a while, which will allow Sprocket to send MIDI over Bluetooth from four momentary buttons, one potentiometer, and one rotary encoder. The toggle shown is an on/off switch for the power to the microcontroller, and the port on the front is a surface-mounted charging port to the microcontroller, which also charges the battery (that silver rectangle inside the cavity).
On my Mac, these electronics show up as a MIDI-Over-Bluetooth device, so it can easily be used to control parameters inside of a DAW; we've also built a hardware "listener" that can receive the Bluetooth data and send it out to other non-computer hardware devices like pedals and a Fractal, but I've been using it to control the effects and other settings in my Ableton Live rig. A few years ago, we began adapting Les Paul's "Les Paulverizer" concept into an actual device, which led us to where we are now with the device inside of Sprocket.
We've got some PCB issues at the moment, but I'm hoping to make a video demo sometime in the coming weeks/months/years
