Here are some simple mods to the Korg Monotron that allow you to use external Controlled Voltage to operate the monotron instead of the ribbon keyboard. I think Korg had a pretty revolutionary thought in letting its customers double as their R&D department to see which way to take the analog revival. Korg release the schematics, and printed all of the controlled voltage points on the PCB. By letting the hackers and tinkerers have at it, some pretty cool things resulted. In the years since this release, Korg has come up with the monotron duo and delay, the monotribe, and the new MS-20 Mini.
For my monotron, I simply connected the CV gate and CV pitch points to RCA jacks and mounted these on the right side of the keyboard. Since I am using my PAIA Fatman as a MIDI to CV converter, the RCA jacks were the easiest way to go.
After connecting the two machines up, I did notice the pitch tracking seemed off. To remedy this, I adjusted the trim pot on the back of the monotron to get closer to the sound I was looking for. While this was better, I found that I could easily add a 100k potentiometer to my cable connecting the CV pitch, and get more adjustment to reach the lower octaves. The results are shown in the video below, where I used the CV controlled monotron as a bassline synthesizer, to create some acid style synth tweaks reminiscent of the mid 1990's stuff I used to DJ.