Many many thanks for posting this (and of course for sharing it). I was making the MIDI to CV from Elkayem but nothing was working.
Then, funny part, i realised that the LEDs were flashing at the correct tempo or gates every time i was switching it off.
What made it go from not working to “working as expected” is the pullup resistor. 500r didn’t work for me. I am using 5k and it works great. (Also works without any btw)
Posting this in case someone follows Elkayem schematic and ran in some issues.
Working with keystep37 and a cheap arduino. 