I have here my Patch SM that keeps sending voltage out of it’s CV outputs, even when I program it to send 0 out of the 4095 position possible. It’s obvious that it is’n’t much, something around 50mV, but it still enough to trigger the Level CV input of my Mutable Instrument’s Plaits. I unconnected my Patch SM from it’s usb plug. Is it normal behaviour? Could It be a ground issue, or maybe because I use two different PSUs for my microcontroller and my module?
Thank you 
Yes, it’s normal behavior, due to variations in op amps, etc. A solution is to add calibration to your firmware to minimize the ‘error’.
Great thank you! I will look into that
The CV outs on the Patch SM are unipolar so you won’t be able to calibrate them to have them send something closer to 0V when sending 0 to the DAC, unfortunately.
You can, however, change libDaisy so that the DAC is initialized in the unbuffered mode as per this PR: Update daisy_patch_sm.cpp DacHandle::BufferState::DISABLED; by IC-Alchemy · Pull Request #630 · electro-smith/libDaisy · GitHub
The CV outputs already have an op amp to buffer the STM32 DAC outputs so the internal buffer is not necessary and this brings the value 0 output voltage closer to 0V (still not perfectly 0V, but definitely closer). Any remaining trimming would have to be done via additional analog circuits.
Oops, I totally forgot they’re unipolar.