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MIDI to CV-Gate Interface MCV-628



To drive analog monophonic CV/Gate synthesizers with MIDI devices.

  • 1V/Oct scale or 48 notes table
  • Positive Gate Output.
  • Pitch CV is 10 Oct range for 1V/Oct
  • Monophonic, true last note playing priority
  • Running status and notes stack are implemented
  • Aux CV is assignable to Velocity or any MIDI controlers
  • Autolearn mode for easy parameters setup
  • All parameters editable by sysex. PC config software available.
  • Ultra simple human interface: 1 led, 1 switch
  • Keep config when off.
  • CV Output voltages 0/+10V - Gate =0/+5V TTL logic 
  • Hardware USART and CPU clock @ 20MHz

Schematic and pcb

 This interface is builded with a PIC16F628 clocked at 20MHz. the hardware. The PIC16F628 have an integrated USART ( serial Port ) also the MIDI port is not a software emulation of the serial port , but a real hardware implementation. Unless to say its more reliable and faster compared to a PIC16F84 at 4 MHz emulating serial port ...The voltage reference is a REF01, more expensive than the TL431, but no need of trimmers & resistors to get a stable +10V reference voltage... For CV output amplifiers i get good results with the LF412 (<+2mV offset) or LM358 ( -1mV!!! ), but most of dual amplifiers work well here. Best one here are precision low drift, low offset ..Trimmers near aops are here to adjust CV scale to 1V/Oct or 10V full scale . They are optionnal , but it is better to keep them for fine calibration of CVs outputs. The interface must be powered by a well regulated +/-15VPSU


Symetrical PSU -/+15VDC (version A)

MCV-628A Schematic (pdf)




Firmware for PIC16F628

The main piece of code, the brain of the interface. To download and "burn" into the PIC16F628. Choose the firmware according to your need, again many hardware compatible versions are available.

MCV-628 firmware v1.12P

1V/Oct or 48 notes table editable by sysex for V/Hz or others AuxCV assignable to Velocity or any MIDI controlers. Gate is positive logic (0=off, +5V=on) Autolearn for channel, Note ref ( transpose), controler number for AuxCV. All parameters for this firmware can be edited in real time with sysex messages. )

Here is the generic asm source code MCV628 v1.12

MCV-628 firmware v1.12N

Same as v1.11P but with negative logic GATE for KORG MS10, MS20 synthesizers (0=on, +5V=off) Note : the Gate Led must be reversed on pcb with the anode connected to +Vcc (and not GND ) to work correctly .

MIDICLOCK 628 firmware

to transform the MCV628 into a MIDI Clock converter/divider like the MC628. The clock pulse signal is present at the gate output..The PC config software for the MC628 can be used to edit parameters.

Blink Test MCV628 Program

This useful file is to try if the PIC is ok. Blink Test source code(ASM) 

The GATE led

It is a multi purpose led! It blink 3 times at power on, after the complete init of the cpu/software. It means "All is ok". In normal working condition, the Gate led ligth when a note is played or if a recognised SysEx message is received. If a trouble happen during SysEx reception, the led will stay on, showing an error has occured. Nothing is written in Eeprom in this case. Any incoming MIDI message will unlock the interface, else it is a fatal error from the PIC, and a cold reset is may be necessary ( very rare case). When the interface is in Autolearn mode, the Gate led stay on, until a MIDI message has been received.

Autolearn Mode

It is the simplest way to set main parameters of the interface. Here how it works: Push Autolearn switch on the interface, the Gate led ligth on. The interface is now in Autolearn mode waiting for the next MIDI message you will send. When the interface receive the message, MIDI channel, note or controler informations are extracted and stored to the Flash memory of the interface. One parameter only is changed at time. The led gate goes off and the interface is now setup with the new value...That's all! Parameters changed by the Autolearn mode are :

  • MIDI channel number : 1..16 . Send any MIDI message with channel number inside.
  • Reference note : 0..127     Lowest note the interface can play ( digital zero) Send a note message
  • Reference controler : 0..127  The contoler number assigned to AuxCV .Send a controler message
MIDI implementation
    Note On 
    All note off
    Pitch CV
    Note stack for true last note played operation
    Running status implemented. 

    firmware <1.1 : AuxCV wired to Mod Wheel ( control 1)
    firmware >1.1 : AuxCV assignable to velocity or any controler

    SysEx  format <F0,ID,CAN,ADR,LSB,MSB,F7> 
     Covers all firmware parameters + 48 notes table stored in Flash eprom. ( only for firmware rev> 1.10)


The PC Config Software

With firmware revision upper than 1.1, the MCV628 memory is fully editable with MIDI exclusive messages.I have written a complete MCV628 editor software for PC under Windows 9x /XP. Very helpful to the interface, with few mouse clics...


Here is a new version of the PC Config Editor for the MCV628. . It replace the V1.1 who seem to do not work anymore with the actual firmware ...I must say that i have loosed the v1.1 source in a hard disk crash few time ago . So i have quickly re-writen it from scratch ... Indeed i have not implemented the table 'feeding' featurre . This software is mainly useful to setup the 1V/Oct mode just after you have burned a new firmware into the PIC - by default it is table mode who is no more used here and see to put in trouble many builders ;) So use the V1.2 Editor with the actual 1.12 firmware .


MCV628 config software V2.8a for PC (unrar , no install required )


For your knowledge ,the table feature is not very useful excepted under very rare situations. V/Hz synths like Lorg MS10/20 should be driven with at least a 12Bits dac like here . Pure 8 bits interfaces like he MCV628 are not enough accurate to emulate a smooth enough expo scale .

The MCV628 is perfect to to drive any 1V/Oct synthesizers like Moogs , Arp , Roland, SCI, or modular VCOs with an excellent accuracy .


Old version !!! - do not use - for archive and the rare diyers who still have a compatible firmware
MCV628 config software V1.1 for PC

Here are screen pictures of the config software v1.1..., the new one is not very different unless there is no more the table feature .

The 48 Notes Table tune editor: the special CV scale showed is to drive a Thyratron tube VCO (2D21) with MIDI in my X2TS tube synth.






MCV628 pcb + construction manual
are available on order

Last Update 17/03/2010
Released in 2003

© Marc BAREILLE 2003-2010