I had wanted to do this mod for a while and hadn't gotten around to it. GlitchDS has a "Strum" mode, and while I may not have the best touch screen strumming rhythm skills, you can just push the RIGHT ARROW key to do the same thing. So I wanted to make a way to electronically "Push" the right arrow button in rhythm. I have seen products like the midify system and what not but didn't really want to spend $40 on a kit I wasn't sure I wanted to spend the time on, and only needed 1/12 of its capabilities. This mod is SIMPLE it is just an 1/8 inch cable hooked up to the GROUND in the DS and the RIGHT ARROW button. Less than $5. I did have to use a ground loop interrupter, however. I am a tinkerer, not an engineer.
GlitchDS to Roland TR-606 Sync Using Nintendo DS Trigger Mod from LifeInABox Productions on Vimeo
Sorry for the sound and video quality, couldn't find the power supply for the good camera.
PS: I am not liable for ANY damage you do to ANYTHING while attempting to do this mod. In fact, don't do this mod. At all. Really.