Simple MIDI

README

Written by Tom Whitwell In Herne Hill, London, October 2024 - October 2025

Hold down the momentary toggle switch on startup
Release the switch 5 seconds after startup
The centre left LED will start to flash
Patch the top oscillator in the Workshop System to an output so you can hear it
Make sure FM is fully off
Use a tuner to the oscillator to C3
Patch the left CV output to the top oscillator 'Pitch' input
If the oscillator changes tune (it probably will, a little bit) you need to calibrate 0V
Flip the toggle switch up
The led will start to flash more slowly
Now you can use the big knob and the X knob as coarse/fine controls to set the position of 0v. Fiddle around until C3 is back in tune
When you're ready, flip the toggle switch down.
Now tap the toggle switch, and the LED will move to the top left LED
This indicates it is sending +2V from the left hand output
Flip the switch up, and tweak the knobs until the oscillator gives a C5 in tune.
Push the switch back to the middle to save that setting, then tap down again to set -2V to C1
Tap the switch again, and the LED will move to the right column, in the middle.
This represents the 0V output for the right hand CV output.
IMPORTANT: Repatch at this point, so the right CV output controls the Bottom oscillator.
(The oscillators aren't calibrated, so each output will be calibrated to a specific oscillator's quirks!)
You can tap through the voltages to check everything is working as it should, flipping up to change any voltages you're not happy with.
Once you're finished, press reset to return to normal MIDI mode.

This card includes several useful classes
However, I (Tom) wrote it, so it's not very well organised, and can certainly be improved.
CV.h is Chris Johnson's delta/sigma code, which pushes 19bit precision from 11 bit PWM
DACChannel.h uses the calibration data to create calibration constants. ChatGPT wrote most of this, so I don't really understand it, but it seems to work.
calibration.h organises the reading and writing of data to the Eeprom, with error checking. This was a Tom + ChatGPT collaboration, hopefully a good basis for incorporating the calibration code in other cards.
- The memory map for calibration makes space for 10x calibration points for both channels, but this only uses 3.
- There are certainly ways to automate the calibration process to make it more precise and easier to use.
Click.h is a little short tap/long tap library I wrote for Startup

Offset	Bytes	Contents
0	2	Magic number = 2001 - if number is present, EEPROM has been initialized
2	1	Version number 0-255
3	1	Padding
4	1	Channel 0 - Number of entries 0-9
5	40	10 x 4 byte blocks: 1 x 4 bit voltage + 4 bits space \| 1 x 24 bit setting = 32 bits = 4 bytes
45	1	Channel 1 - Number of entries 0-9
46	40	10 x 4 byte blocks: 1 x 4 bit voltage + 4 bits space \| 1 x 24 bit setting = 32 bits = 4 bytes
86	2	CRC Check over previous data
88		END

Board: Generic RP2040 Flash Size: 16MB (No FS) CPU Speed: 133MHz Boot Stage 2: W25Q16JV QSPI/4 (for the newer 2mb cards) USB Stack: Adafruit TinyUSB

To install the UF2: Push the boot select button (remove the main knob on Computer), it's on the right
Connect the front USB to the computer
Hold down boot and tap reset (the button at the bottom by the card slot
A folder should appear on your desktop called RPI RP2
Drag simplemidi.uf2 into that folder
The system should reboot and the folder disappear
Now check your DAW for midi interfaces - you should find one called Music Thing Workshop System MIDI or something similar to that