CV2MIDI



Full tracks of Analog-Monster project on YouTube channel Sushonyo Synth Project
Full tracks of Analog-Monster project on SoundCloud channel Analogmonster



Introduction:

This module is the result of a request by Hans-Joachim Helmstedt, the developer of the Formant MSS2000 Modular Synthesizer and the author of the corresponding book. He asked me to design a module to integrate a non-MIDI ratcheting sequencer and other non-MIDI equipment like his theremin in his mainly MIDI based studio.

I liked this idea, so I developed a highly versatile module which contains 8 independent cells to convert an analog control voltage at a CV input into a MIDI NOTE ON / NOTE OFF sequence, following a clock / gate input.

But not enough, by using the three switches at the module upper side one can set a binary combination between 0 and 7 which determines different programs each to be executed by the module. With these programs the module becomes a universal CV2MIDI processor for different purposes.

Following a description of the module and its programs which have been developed so far.

The CV2MIDI module:

  • Program selection with three switches by setting a binary combination between 0 and 7.
  • Display block with 8 LEDs to show the clock / gate activities.
  • Block of 8 CV / CLOCK pairs.
  • ISP port for software updates with /RESET trigger for the microcontroller.
  • MIDI output with display LED for MIDI activity.
  • Program 0: All cells work independently. Each cell converts the analog voltage at the CV input jack (0V to 5V) into a MIDI note value between C0 and C5 on detecting a rising edge at the corresponding CLK input jack (5V). A NOTE ON sequence on channel 1 to 8 (dependent on the input cell) with a default key velocity of 0x7f is created and sent. A falling edge at the CLK input creates and sends the corresponding NOTE OFF sequence (= velocity 0x00). A missing input voltage at the CV input jack is interpreted as 0V / C0 note. Sequence example for the Note C1 at CV1: 0x90 0x0c 0x7f - 0x90 0x0c 0x00.
  • Program 1: With this program the module becomes a MIDI sequencer! Only CLK1 is scanned. A clock signal here converts all 8 CV inputs in a sequence according to the clock speed. The resulting MIDI sequence output corresponds to Program 0.
  • Program 2 and 3: Two more sequencer modes: Backwards and Knight Rider mode, meaning forwards and backwards! The same sequence creation.
  • Program 4: Only CV1-CLK1, CV3-CLK3, CV5-CLK5 and CV7-CLK7 are used as note value inputs, all other CLK inputs are not considered and the other CV inputs are converted into key velocity values and used in the NOTE ON sequences. CV1-CLK1, CV3-CLK3, CV5-CLK5 create NOTE ON sequences on channel 1 (0x90), CV7-CLK7 on channel 10 (0x99) to control drum mashines (request from Hans-Joachim Helmstedt).

Circuit: Click here: KiCad-Schaltung
The circuit is made around the microcontroller ATmega8535.
CV inputs: A control voltage input is mixed with an offset compensation voltage and converted by one of the 8 ADC channels of the controller. Voltages up to 5V DC can be converted; 0V is converted to C0, 5V to C5. This converted note value is sent as part of the MIDI NOTE ON sequence via MIDI OUT.
CLK inputs: A clock or gate input is inverted by a transistor, leveled to 5V and transferred to a digital input port of the controller. On scanning a rising edge at the CLK input the software converts the analog voltage at the coresponding CV input to a MIDI note value and sends the NOTE ON sequence. According to the chosen program the default key velocity 0x7f is used or the converted voltage at the next CV input jack (see Program 4). On detection of a falling edge the corresponding NOTE OFF sequence is created and sent.
Program selection: Three switches select one of eight programs according to the chosen bit combination. LEDs show the selected proram addtitionally (see demo videos). The switch positions are interpreted at corresponding digital ports of the controller.


Full tracks of Analog-Monster project on YouTube channel Sushonyo Synth Project
Full tracks of Analog-Monster project on SoundCloud channel Analogmonster


Please send questions or remarks to:
Carsten Toensmann

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