Here is a Game Boy LSDJ / Nanoloop 1.x sync device that shows up natively as a USB MIDI device, thereby requiring no drivers and no power beyond the standard USB connection.
In terms of soldering, it is very easy as well, as it only requires two connections for each Game Boy sync cable, and that's it.
This is a very cheap and easy project to make: the Teensy board costs $16. You will most likely already have a USB A to mini B cable and a Game Boy link cable.
Things You Need
Music or audio software that can output MIDI Beat Clock
Teensy 2.0 board
Game Boy link cable that you can splice
Upload the Teensy_GB_Sync.hex file to the Teensy via the Teensy loader software.
If you would like to edit the source code, you need to update the Teensyduino core to include MIDI Beat Clock messages. See here for more information.
Here is the pinout of the Game Boy link cable:
To synchronise your Game Boy, you will need to splice the Game Boy link cable and find GND (ground), SI (serial in) and SC (serial clock).
To sync to LSDJ, connect ground on the Teensy board to ground on the Game Boy link cable. Also, connect digital Pin 0 on the Teensy board to SC on the Game Boy link cable.
To sync to Nanoloop 1.x, connect ground on the Teensy board to ground on the Game Boy link cable. Also, connect digital Pin 1 on the Teensy board to SI on the Game Boy link cable. Note that you will need to add a resistor to the connection going to SI in order to sync with Nanoloop 2.x.
Demo Video - LSDJ Synchronised to Ableton Live