Midi2CV Mk2 is a DIY embeddable MIDI to 4 x CV/Gate converter with extensive configuration options and extra modulation sources (LFO and AHDSR EG).

Specifications

POWER SUPPLY

• +-12V or +-15V, Euro or MOTM power connector
• 50mA@+15V, 10mA@-15V

OUTPUT

• 4 x CV channels, each could be 0+5V, 0+10V or -5+5V, configurable by jumpers
• 4 x Gate channels, 0+5V, 0+7V or 0+10V, configurable by a jumper

MIDI IN LED

• optional MIDI IN LED, blinks when receiving MIDI events

GATE LED

• optional GATE LED, lit when a note is on

MIDI IN

• MIDI IN connector

MIDI OUT

• optional MIDI OUT connector, mirrors MIDI IN

LEARN SWITCH

• hold down during power up to enter firmware update mode via MIDI
• hold down while receiving a note to learn MIDI Channel (v2.03+)
• hold down while receiving control change to learn control CV parameter
• hold down while moving pitch wheel up/down to turn note tuning mode on and off
• hold down for 10 sec while the device is idle to reset the device to default settings
• hold down and release in less than 5 seconds to reboot the device

WebMIDI configuration and firmware updates (v3.50+)

Navigate your browser to the Midi2CV Mk2 configuration page and select MIDI port names your Midi2CV Mk2 is connected to. Note that you need the two way connection: computer MIDI interface MIDI OUT port should be connected to Midi2CV MIDI IN, and Midi2CV MIDI OUT port should be connected to computer’s MIDI IN port.

Using Midi2CV Mk2 configuration you can do the following:

• query currently installed firmware version
• update firmware to the latest version
• view and change all the device configuration settings
• send and receive device not pitch tuning data

Important: at this time only Chrome and Edge are known to support WebMIDI reliably. Firefox and Opera may work too.

On-board switches

SW1-4 specify default base MIDI channel

• MONO, DUO and POLY modes use the base channel
• QUAD mode uses base channel, base channel +1, +2 and +3

1234 ch     1234 ch
.... 01     ...X 09
X... 02     X..X 10
.X.. 03     .X.X 11
XX.. 04     XX.X 12
..X. 05     ..XX 13
X.X. 06     X.XX 14
.XX. 07     .XXX 15
XXX. 08     XXXX 16

SW5-6 specify operation mode:

• MONO — classic monophonic mode with last note priority
  CV: note, velocity, after touch, control
  Gate: gate, strobe, start, clock
• DUO — classic duophonic mode
  CV: note1, note2, velocity, aftertouch
  Gate: gate, strobe, start, clock
• QUAD — four pitch CVs on adjacent MIDI channels
  CV: note1, note2, note3, note4
  Gate: gate1, gate2, gate3, gate4
• POLY — true polyphonic voice allocation
  CV: note1, note2, note3, note4
  Gate: gate1, gate2, gate3, gate4

56 Mode
.. mono
X. duo
.X quad
XX poly

Note CV: 1V/Oct pitch CV with optional micro tuning: every note can be set to output any CV level within selected output range. Can be used for Hz/V, alternate tuning schemes, or to correct VCO tracking imperfections. Note tuning is configured using special operation mode, and could be saved, restored or loaded via a sysex message from a computer.

Velocity CV: linear by default, however, you can choose to adjust velocity response curve making it softer, harder or wider:

After touch CV: linear by default, however, you can choose to adjust the after touch response curve making it softer, harder or wider, similar to velocity CV above.

Control CV: by default, this CV tracks CC 1 (Modulation Wheel) value, however, it could be set to track any CC from 1 to 119. Control change number can be “learned” on the fly: hold down the LEARN switch and turn/click the desired control knob/button.

Gate: goes high when a key is down, low when no keys are down. If “strobe gate” option is in effect, gate signal is pulled down for the duration of the strobe every time a key is pressed while some other key is down. This allows envelopes to re-trigger for synths that don’t have Strobe input.

Strobe: goes down for 1 to 5 ms, occurs each time a key is pressed. Strobe length and polarity are configurable by sending a sysex message and the setting is persisted in EEPROM.

Start: goes high when MIDI Start/Continue message is received and down when MIDI Stop message is received.

Clock: goes down for 1 to 5ms each time MIDI clock message is received, could be divided down to 32 triplet, 32th note, 16 triplet, 16th note, 8th note triplet, etc. all the way to 2 bar note. Division factor is configurable by a sysex and the setting is persisted in EEPROM.

MIDI Channel

On-board switches SW1-4 specify the default MIDI channel. Midi2CV Mk2 uses this channel when it is first started or is reset to default settings. You can change Midi2CV Mk2 MIDI channel by changing these switches or “learning” it from a note played while holding down the LEARN switch. The “learned” MIDI channel will be in effect until the device is reset, in which case the default MIDI Channel specified by DIP switches will be used.

LFO and EG

Starting with firmware version 2.0, Midi2CV Mk2 provides two extra modulation sources: LFO and AHDSR EG which can be assigned to any CV output. These modulation sources are controlled by MIDI CC commands sent from an external MIDI controller connected to MIDI IN.

LFO specifications:

• frequency: 0.1-100Hz
• basic waveshapes: sine, sweep, lumps, spike, sine3, sine5, triangle, ramp up, ramp down, square, random sample&hold, random lines, noise
• phase distortion waveshaper
• wave steppyness
• free running or reset on note on
• fade in 0 – 10sec
• bipolar or unipolar
• amplitude control

EG specifications:

• segments: Attack, Hold, Decay, Sustain, Release
• segment duration: 0-15sec
• segment shape: linear, expo, sine
• legato retrigger: on / off
• MIDI Clock retrigger: 1/32T – 2bars
• auto gate control – 0-15sec (similar to MS-20 EG)
• looping: off, gated, auto
• inverted: on/off
• amplitude control

In looping mode EG can be used as a fancy LFO with the shape composed by four linear, exponential or sinusoidal segments with the duration specified by Attack, Hold, Decay, Sustain and Release controls.

Software pitch bend

Starting with firmware v3.10, Midi2CV Mk2 supports software pitch bend: note CV is affected by MIDI Pitch Bend events according to pitch bend range in semitones set by the 0Bh sysex command. If pitch bend range is set to 0, software pitch bend is effectively disabled. The pitch bend range setting does not affect hardware Pitch Bend CV.

Polyphonic port mapping

When polyphonic port mapping is enabled and the device is in MONO mode, all CV/Gate outputs will have the same note info. This enables a unison mode in polyphonic setups where each CV/Gate is permanently connected to a voice circuitry. In DUO mode polyphonic port mapping allows duophonic unison mode: single note info is sent to all CV/Gate outputs but when two notes are played, there are two pairs of different CV/Gate outputs.

Note CV tuning

The default note CV tuning is 1V/Oct for output range 0-10V and -5+5V ranges, and 0.5V/Oct for 0-5V range.

To enable note CV tuning mode, hold down LEARN switch and move Pitchbend wheel up, then release LEARN switch and return Pitchbend wheel to neutral.

To disable note CV tuning mode, hold down LEARN switch and move the Pitchbend wheel down, then release LEARN switch and return Pitchbend wheel to neutral.

While note tuning mode is in effect, hold down a key and use the pitch wheel to adjust the note’s pitch. Release the key to remember the  note’s pitch.

You can also use Control Change messages to reset, increment/decrement and interpolate note tuning, see the CC table below.

Control Change messages

LFO and EG control CCs (v2.0+):

Parameter	CC	Description
LFO CV	90	0 – none 1 – CV1 2 – CV2 3 – CV3 4 – CV4
LFO Shape	91	0 – sine 1 – triangle 2 – ramp down 3 – ramp up 4 – square 5 – lumps 6 – sweep 7 – spike 8 – sine3 9 – sine5 10 – random S/H 11 – random lines 12 – noise
LFO Rate	92	0 – 127, 0.1 – 100Hertz
LFO Sync	93	(reserved, [TBI])
LFO Reset	94	0 – free running 1 – reset on note on
LFO Fade in	95	0 – 127, 0 – 10sec
LFO Amplitude	96	0 – 127
LFO Bipolar	97	0 – unipolar 1 – bipolar
LFO Waveshape distortion	98	0 – 127
LFO Waveshape steppyness	99	0 – 127
EG CV	100	0 – none 1 – CV1 2 – CV2 3 – CV3 4 – CV4
EG Attack	101	0 – 127, 0 – 15sec
EG Hold	102	0 – 127, 0 – 15sec
EG Decay	103	0 – 127, 0 – 15sec
EG Sustain	104	0 – 127
EG Release	105	0 – 127, 0 – 15sec
EG Gate	106	0 – 127, 0 – 15sec
EG Amplitude	107	0 – 127
EG Shape	108	0 – linear 1 – expo 2 – sine
EG Retrigger	109	0 – don’t retrigger on legato notes 1 – retrigger on every note on
EG Loop	110	0 – none 1 – loop while note is held down 2 – loop endlessly
EG Sync	111	Retrigger EG in sync with MIDI Clock 0 – none 1 – 1/32T 2 – 1/32 3 – 1/16T 4 – 1/16 5 – 1/8T 6 – 1/16D 7 – 1/8 8 – 1/4T 9 – 1/8D 10 – 1/4 11 – 1/2T 12 – 1/4D 13 – 1/2 14 – 1T 15 – 1/2D 16 – 1 17 – 2T 18 – 1 1/5 19 – 2
EG Invert	112	0 – normal 1 – inverted

While in note tuning mode Midi2CV Mk2 recognizes the following control messages:

CC	Value	Action
115	> 0	Reset all notes tuning
116	> 0	Reset last note tuning
117	> 0	Increment last note tuning
118	> 0	Decrement last note tuning
119	> 0	Interpolate last note tuning

You can also use pitch wheel to quickly get note tuning into required range.

Sysex data format

Sysex message format:

0xf0, // Sysex
0x29, // PPG manufacturer ID
'2','C','V',0x00, // Midi2CV Product ID
// * Command byte (SysexCmd)
// * Modifier byte (SysexMod)
// * Payload bytes (nibbelized)
0xf7 // Sysex end

Sysex commands:

0x00, // request action, mod=action, see SysexMod (v3.50)
0x01, // set continuous controller number 0-119
0x02, // set strobe width 0-4: 1-5ms
0x03, // set clock divider 0-19: see intervals.h/cc
0x04, // set tune data 128 x int words of tune data
0x05, // set velocity curve, 0-8: linear, soft1/2/3, hard1/2/3, wide1/2
0x06, // set aftertouch curve, 0-8: linear, soft1/2/3, hard1/2/3, wide1/2
0x07, // set number of poly mode voices, 1-4 (v3.00+)
0x08, // set invert strobe mode: 0 - positive, 1 - negative (v1.11+)
0x09, // set invert gate mode: 0 - positive, 1 - negative (v1.12+)
0x0A, // set strobe gate mode: 0 - off, 1 - on (v1.13+)
0x0B, // set pitch bend range: 0 - disable, 1-12 semitones (v3.10+)
0x0C, // set poly port mapping: 0 - disable, 1 - enable (v3.50+)
0x0D, // set software MIDI THRU: 0 - disable, 1 - enable (v3.51+)
0x7F, // set all device settings at once

Sysex modifiers:
0x00, // reset device, only for SYSEXCMD_REQUESTACTION (0x00)
0x01, // update firmware, only for SYSEXCMD_REQUESTACTION (0x00)
0x7e, // request state reply SysEx
0x7F, // request state that is set by the command


Firmware update

Midi2CV firmware update steps:

1. Connect your MIDI interface output to Midi2CV MIDI IN
2. Power on Midi2CV while holding down the LEARN switch. LEDs will blink shortly then MIDI IN LED will stay steadily lit. Alternatively, you can request firmware update by sending ‘request_firmware_update.syx’ file to MIDI IN.
3. Send firmware update sysex file (*.syx) to your MIDI interface port with 250ms delay between sysex buffers. Elektron’s C6 works great on OS X and Windows. Classic MIDI-OX is also good on Windows. MIDI LED will be blinking while firmware sysex is being received. On successful update, LEDs will blink 3 times one after another. On error, both LEDs will blink together 5 times.

Starting with firmware version 1.14 you can request firmware update without using LEARN switch by sending REQUEST ACTION sysex 0x00 with modifier byte set to 0x01. This facilitates firmware updates for applications where LEARN switch is not present or is difficult to access.

Revision history

v.3.57 11/02/2023

• Optimized LFO/EG CC handling to prevent choking, thanks to Ben A.M.
• Reordered LFO shapes for convenience (most popular go first)
• Changed LFO fade in curve to be more gradual

v.3.55 09/16/2023

• Implemented damper pedal support (CC 64)
• Implemented UNISON4 and UNISON2 options for polyphonic setups
• Implemented Enable Soft MIDI THRU option
• Improved DAC precision at high notes
• If LEARN switch is pressed and released in less than 5 secs with no MIDI input reboot the device
• Revamped SysEx handling, added SYSEXCMD_DEVICESTATE and command modifiers in order to enable web page settings management.
• Fixed problem with note tuning wrapping up to the top when pitch bend is  moved all the way down
• Optimized LFO and EG control change handling to prevent device choking on fast MIDI streams

v.3.42 10/27/2022

• Fixed subtle stability issue with gate output, thanks to Chris G.
• Fixed problem with release key retrigger that would retrigger just triggered note.

v.3.40 01/30/2022

• Replaced DUAL mode with classic DUOphonic mode. If you need old DUAL mode please consider using QUAD mode and strobe gates.

v.3.30 01/27/2022

• Replaced PitchBend CV with AfterTouch CV.

v.3.20 08/05/2021

• Fixed problem with note tuning introduced in previous update, thanks to GregC.

v3.10 05/19/2021

• Implemented software pitch bend support with configurable range of 0 to 12 semitones.
• Fixed probelms with MIDI channel number wrap around when base channel is set to 16 in DUAL or 14, 15, 16 in QUAD modes.

v3.00 11/30/2020

• Replaced DRUM mode with POLY mode that provides up to 4 channels of true polyphonic voice allocation.
• Re-worked MIDI I/O implementation eliminating jitter and minimizing soft MIDI Thru delay.

v2.03 6/24/2017

• Implemented MIDI Channel LEARN feature.

v2.02 5/23/2017

• Fixed problem with clock output generating clock at incorrect frequency after receiving MIDI Stop followed by MIDI Continue events. Thanks to Benjamin for reporting.

v2.01 3/8/2017

• Implemented more musical LFO fade in

v2.00 3/7/2017

• Added LFO and EG

v1.14 1/10/2017

• Set note CVs to C4 upon start or reset
• Added ability to request firmware update by sysex

v1.13 11/3/2016

• Added “strobe gate” option and sysex

v1.12 07/02/2015

• Added gate polarity option and sysex

v1.11 06/17/2015

• Fixed problems with All Notes Off handling
• Added strobe polarity option and sysex
• Added firmware version request sysex

v1.10 02/14/2015

• added Drum Mode
• changed Note Tuning mode activation to LEARN+PitchBend
• fixed nasty EEEPROM initialization bug

DIY Resources

Bill of Materials: Midi2CV Mk2 BOM

Firmware: Midi2CV_Mk2_v357

Sysex files: Midi2CV_Mk2_v355_syx

Schematics: midi2cv_mk2

Firmware source code: midi2cv_mk2_300_src

Board outline (1:1 PDF): midi2cv_mk2

Ordering Midi2CV

To order Midi2CV, please send an email to pete at kvitek  c o m specifying how many PCBs and pre-programmed MCUs you need, a country where to ship them, and an email address to send the PayPal invoice to.

Prices (US dollars):

Midi2CV PCB — $25
Pre-programmed ATMega328p — $10
2 x MCP4922 DAC ICs — $10

Shipping:

Continental USA — $5 (California residents add 8.75% tax)
Canada – $15
Europe – $20
Australia – $20

Please make sure your PayPal shipping address is correct!

Midi2CV in 5U format

Parts

MIDI LEARN switch: E-Switch PV2S240NN — DigiKey, Mouser
DIN MIDI connectors: CUI Devices SD-50SN — DigiKey, Mouser
1/4″ connectors: Switchcraft 112AX — DigiKey, Mouser

MOTM

FrontPanel Express panel: 1U_MIDI2CV

MU

Vector format panel: Midi2CV_MU_panel

I have a few of these available for sale, please email me at the address specified on the ordering page.