This isn’t necessarily the best or easiest way to convert MIDI to CV but I’ve written up how this can be done fairly easily with a microcontroller and an (isolated) MCP4728 4 channel DAC for four octave pitch CV. It’s also easy to add more of the same DACs to this, either via the second connector or (more fiddly) using multiple i2c addresses.
Instructables: Microrack Modular Synth: MIDI to CV Using Cytron Maker Nano 2040 and Adafruit MCP4728 DAC With I2C Isolation
I’m not exactly sure of the functionality provided by the default firmware on Microrack’s midi→cv module. I suspect my efforts are inferior but worth considering if you want an immediate solution or like tinkering with microcontrollers (in CircuitPython). My demo video is using envelopes generated by CircuitPython’s synthio.
1 Like
Oh wow, you also use MCP4728!
Right now we are working with Playtronica on ESP32-S3 based module to connect any USB devices and get cv/gate signal from USB MIDI. Someone can already seen it on last superbooth. Hope we will release it at the end of this summer!
unfortunately, it based on esp32 without USB so you only got usb-uart, not full usb midi. Out of the box only hardware (TRS) midi is available.
Of course you can use software to create virtual midi based on serial device, but it is more difficult.
This is a good example where you shouldn’t use +5V rails for powering DAC because it is unstable, so for this case local LDO powered by +12 rail is the best solution to provide you stable reference which is not depend on any external noise.
As for converting i2c from 3V to 5V there is elegant solution based only on two MOSFETs:
For i2c, I’d seen Adafruit have a bi-directional level converter using MOSFETs and I bought some cheap similar ones a while ago to play with but these don’t have the convenient STEMMA/Qwiic connectors. I wanted to do something that was quick and easy for others to setup although the DAC board does need the headers soldering on which in this case is unfortunate. I was also interested in exploring the ground isolation. I still don’t have a good grasp of all of the issues with grounds and electrical/audible noise.
BTW, I’m sure you’re aware of this but every (?) Espressif microcontroller has ADC quirks which are important to understand if you are using them. I’ve taken a casual look at the ESP32 and ESP32-S2 (not S3) in the past. To my surprise Espressif actually documented them last year.
Over in the Eurorack world there’s a surprisingly cheap module using the ESP32-S3 which does loads of stuff including MIDI to CV: AMYboard
1 Like
