Simple MIDI USB Clock Converter for Analogue Sequencers

Title says it all really. I have several analogue sequencers that I designed and built years ago and I clock them with a Kenton Pro Solo Mk3. This unit can switch the MIDI THRU port to SYNC24 mode to work with Roland Drum Machines. This is a great solution but does tie up my Kenton which uses with my Editor and needs MIDI THRU for 2 way comms.

Arduino and the Pro Micro 

I realised it was a simple job to reprogram on of my Pro Micros to convert MIDI Clock and Stop/Start messages. I've used it for a few weeks and its a worker so I thought I build proper unit:

• Pro Micro
• 24 Pin DIL Socket
• 1 x PCB Mounting 1/4 Stereo Jack Socket (my sequencers are all 1/4)
• 1 x 10K pot (I used a 47K pot)

Like my SYNC24 breakout box this will be mounted on the back of an existing 19" rack panel.

The code is at the bottom of the post - you  will need to install the MIDIUSB.h library

Analog pulses are output on the clock jack connected to Pin 2. When stop is pressed on the sequencer the Stop command  $FC is picked up and a RESET pulse is sent out on Pin 5. This is connected to the RESET IN on my sequencer. This ensures the analogue sequencer is set to STEP 1 before the next MIDI clocks $F8 are received. I don't need to use a START pulse as my sequencer will start on the next clock pulse.

Pin A10 is connected to a 47K pot to adjust the clock divide ratio. Stop the sequencer before changing this value.

The MIDI Start command $FA is used to ensure the first Clock Pulse is sent out and that the RESET line goes LOW

/*

 * BasicMidiClockDiv.ino

 * Tested on Logic 10.6 and Ableton Live 9

 * Proves Clock Out, Reset and CLock Divide

 */

#include "MIDIUSB.h"

#define CLK 5    // Clock 

#define RST 2      // Reset  

#define DEADBAND    24

// Pin A10 uses a 10K (47K) pot to set Clock Divide

//Pulse per quarter note. Each beat has 24 pulses.

//Tempo is based on software inner BPM.

int ppqn = 0;

int ClkOn = 2 ;

int ClkOff = 5 ;

int prev_val;

int value ;

void setup() {

  Serial.begin(115200);

  pinMode(RST, OUTPUT);

  pinMode(CLK, OUTPUT);

}

void loop() {

  midiEventPacket_t rx;

  

  do {

    rx = MidiUSB.read();

    //Count pulses 

    if(rx.byte1 == 0xF8){

       

       if(ppqn == 1) {

      

           digitalWrite(CLK,HIGH);

                      }

       

       if(ppqn == ClkOn) {

           digitalWrite(CLK,LOW); 

                      }

       

       if(ppqn == ClkOff) {

        ppqn = 0;

       }

       ++ppqn ;

                      }

     //Clock start byte

    else if(rx.byte1 == 0xFA){

   digitalWrite(CLK,HIGH);

// digitalWrite(RST,LOW);

      ppqn = 0;

    }

    //Clock stop byte

    else if(rx.byte1 == 0xFC){

        //   MidiUSB.flush();

         digitalWrite(RST,HIGH);

         digitalWrite(CLK,LOW); 

         delay(200);

         digitalWrite(RST,LOW);

          

      ppqn = 0;

                             }

    

  } while (rx.header != 0);

// CLOCK DIVIDE 

  value =  analogRead(A10);

    // Get difference from current and previous value

  int diff = abs(value - prev_val);

// Exit this function if the new value is not within the deadband 

if (diff <= DEADBAND) return;

  // Store new value

  prev_val = value;

  // Get the 7 bit value

  int val2bit = value >> 7;  

  Serial.print(val2bit);

  Serial.println();

 

    prev_val = value;

    //  <3 <6  <12  < 24 1/16 1/8 1/4  1/2

    switch (val2bit) {

  

    

    case 0:

    ClkOn = 1;

    ClkOff = 2 ;

        Serial.print(val2bit);    

        Serial.print(ClkOn );

        Serial.println();

    break ;

 

    case 1:

    ClkOn = 2;

    ClkOff = 3 ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );

    Serial.println();

    break ;

    case 2: 

    ClkOn = 3 ;   

    ClkOff = 6 ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );

    Serial.println();

    break ;

    case 3: 

    ClkOn = 4 ;   

    ClkOff = 8 ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );

    Serial.println();

    break ;

    case 4: 

    ClkOn = 6;

    ClkOff = 12 ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );

    Serial.println();

    break ;

      

    case 5:  

    ClkOn = 8;  // triplet

    ClkOff = 16 ;

    Serial.print(val2bit);     

    Serial.print(ClkOn );

    Serial.println();

    break ;

    case 6:      

    ClkOn = 12;

    ClkOff= 24 ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );     

    Serial.println();

    break ;

    

    case 7:      

    ClkOn = 24;

    ClkOff= 48   ;

    Serial.print(val2bit);    

    Serial.print(ClkOn );     

    Serial.println();

    break ;

    }

 

   // }

    

}