In the video I show how to control a Korg Monotron with a Korg SQ-1 sequencer via CV-Gate using a very simple passive DIY interface.
It's necessary to add the pitch and gate on the Monotron only;
on the PCB this points are well identified, no other change is required; to extract the two cables I used the holes already present on back of the Monotron case so no drilling is required;
this modification is very simple to realize.
In the video you also can see the schematic and the layout of the interface that I made.
To connect the SQ-1 to the interface you need to use the "littleBits OUT" and select the option CV A Range to 5V and CV A Behavior to Chroma; the monotron accepts a CV range approximately between 1.5 and 5 volts.
Enjoy !