Table of content

• Assignment
• My Work
• Group work
• Network - host MQTT configuration
• System context
• Publish musical notes
• Subscribe message and play instrument
• Solenoid
• Circuit for solenoid
• Example sounds by solenoid
• Stepping motor
• Design of slide guitar machine
• 3D design
• Bill of materials
• Making slide guitar machine
• Assembling
• Making slide guitar machine (timelapsse)
• Software
• Performance by slide guitar driven by MQTT beat
• Files
• Lessons Learned
• References

I made slide guitar machine and built system to drive separated instruments at a distanced location. The name of this project is Machine Orchestra at Distant Society (a.k.a. MODS) collaborated by FabAcademy students at Fanlan Kamakura and Kannai.

Summary of group work is written in group assignment page of Fablab Kamakura

I hosted MQTT broker on AWS IoT and configured things, certification and security, policy.

The purpose of this is benchmarking MQTT for validating configuration, coding and performance. The conclusion of benchmarking is "it's useful and worth using MQTT as a networking infrastructure to make a "distributed musical device" idea, that Japan Fabacademy 2020 students work together for make musical device for each home location and play it together in remote place. This project is for group assignment of mechanical design and machine design week.

I described detail in

• MQTT message publishing/subscribing by Message Broker on AWS IoT in individual page
• client sample code and guideline to connect as a MQTT client in group assignment page for the other students.

  var interval = msg.delay;
  var seq = msg.seq;

  function makeNotes(t1, t2, t3, t4, t5, t6){
      msg.payload =  {
          "seq":seq,
          "count": msg.count,
          "t1":t1,
          "t2":t2,
          "t3":t3,
          "t4":t4,
          "t5":t5,
          "t6":t6,
          "interval": interval
      }
  }

  var beat = seq % 8;
  switch(beat){
      case 1:
          makeNotes(60, 55, 60, 1, 0, 1); // ド ソ C
          break;
      case 2:
          makeNotes(67, 64, 60, 0, 1, 1); // ソ ミ C
          break;
      case 3:
          makeNotes(64, 60, 60, 1, 0, 0); // ミ ド C
          break;
      case 4:
          makeNotes(71, 55, 60, 0, 1, 1); // シ ソ C
          break;
      case 5:
          makeNotes(67, 60, 60, 1, 0, 0); // ソ ド C
          break;
      case 6:
          makeNotes(69, 64, 60, 0, 1, 1); // ラ ミ  C
          break;
      case 7:
          makeNotes(67, 60, 60, 1, 0, 1); // ソ ド C
          break;
      default:
          makeNotes(64, 60, 60, 0, 1, 0); // ミ ド C
  }

  return msg;

At function node named "make note" on Node-RED, message is constructed for each "beat"(beat sequence that is started from 1 when music is started) (26 May, 2020)

  var interval = msg.delay;
  var seq = msg.seq;
  
  function makeNotes(t1, t2, t3, t4, t5, t6){
      msg.payload =  {
          "seq":seq,
          "count": msg.count,
          "t1":t1,
          "t2":t2,
          "t3":t3,
          "t4":t4,
          "t5":t5,
          "t6":t6,
          "interval": interval
      }
  }
  
  function checkNote(note){
      if (note > 72) {
          note = note - 12;
      }
      if (note < 60) {
          note = note + 12;
      }
      return note;
  }
  
  function melodySequence(seq, t1s) {
      var beat = seq % 8;
      var t1;
      
      switch(beat){
      case 1:
          //t1 = checkNote();
          makeNotes(t1s, 1, t1s, 1, 0, 1); // ド ソ C
          break;
      case 2:
          t1 = checkNote(t1s + 7);
          makeNotes(t1, 2, t1s, 0, 1, 1); // ソ ミ C
          break;
      case 3:
          t1 = checkNote(t1s + 4);
          makeNotes(t1, 3, t1s, 1, 0, 0); // ミ ド C
          break;
      case 4:
          t1 = checkNote(t1s + 11);
          makeNotes(t1, 4, t1s, 0, 1, 1); // シ ソ C
          break;
      case 5:
          t1 = checkNote(t1s + 7);
          makeNotes(t1, 5, t1s, 1, 0, 0); // ソ ド C
          break;
      case 6:
          t1 = checkNote(t1s + 9);
          makeNotes(t1, 6, t1s, 0, 1, 1); // ラ ミ  C
          break;
      case 7:
          t1 = checkNote(t1s + 7);
          makeNotes(t1, 7, t1s, 1, 0, 1); // ソ ド C
          break;
      default:
          t1 = checkNote(t1s + 4);
          makeNotes(t1, 8, t1s, 0, 1, 0); // ミ ド C
          break;
      }            
  }
  
  var beat = seq % 8;
  switch(1 <= beat && beat <= 4){
      case true:
          melodySequence(seq, 60); // C
          break;
      case false:
          melodySequence(seq, 65);  // F
          break;
  }         
  return msg;

For mitigating delay in publishing, I changed the internet connection from Wifi to LAN cable. It would add the stability to the messsaging performance.

I used 3 set of following materials and connect it to data pins(S1: 4, s2: 16, S3:17) at ESP32 Devkit C in parallel.

For supplying sufficient voltage for this circuit (x 3 parallel), I used separated battery box(1.5V x 4).

Ref: a Japanese blog article: ソレノイド(ZHO-0420S-05A4.5)をArduinoとMOSFETで動かしてみた！

(I made left circuit diagram by Tincar CAD)

2-phase stepping motor (KH42KM2-802) by Nedic, Used

Motor driver(A4988) by HiLetgo

Connection between A4988 motor driver and motor cables (from Original Mind) is like this.

• 2B - black
• 2A - brown
• 1A - yellow
• 1B - orange

Pinmap of A4988 (from lastminutengineers.com) is like this.

I used pins of:

• VMOT - 12V AC Adapter (AC adapter supply voltage by 12V - max 1.2A)
• GND - AC Adapter(Ground)
• 2B - black cable of stepping motor
• 2A - brown cable of stepping motor
• 1A - yellow cable of stepping motor
• 1B - orange cable of stepping motor
• VDD - 5V VCC of ESP32(to control SETP/DIR pin)
• GND - GND of ESP32
• SETP - 25 IO pin of ESP32
• DIR - 26 IO pin of ESP32

Seeing a tutorial about A4988, I limit the maximum amount of current flowing through the stepper coils and prevent it from exceeding the motor's rated current.

Imax=Vref/0.4 means Vref=Imax*0.4=1.2*0.4=0.48V

So I adjusted tiny screw and found the point that the voltage between the potentiometer and ground-pin near 0.48V. This works and the stepping motor finely.

With help of my instructor Tamiya-san, I got a concept to use stepping motor to slide the arm along with the neck of guitar.

For making the base of arm stable, I changed the design of the machine.

Also, I changed to attach screw as a central axis into belt and pooley for increasing moving speed of code change performance of slide guitar.

It's important to tighten right belt in these pictures without touching other materials.

Belt presser parts is originally from shared material.

I splitted components of it and expanded the size, embed it into table design. Table design is for attaching to TAMIYA universal plate that has 3mm hole with 5mm spaces.

It's difficult to insert belt to 3D printed parts as the slit is very narrow. I needed to hit the belt from top by rubber mallet to settle the belt in slit of the parts.

Through experiment, I occasionally needed to check if nut under belt pooley in bearing side is loosened. As the screw is tightly pulled by belt and idle spinning of belt applys pressure to pooley, this nut is loosened and it brings belt touch to the other materials. All that process cause unexpected behavior of moving table. So, I checked this part time by time to make the machine stable.

For the part of attachment of actuator like solenoids or bottleneck of slide guitar, I used "universal arm" of toy kit by TAMIYA INC, a hobby kit company in Japan.

I attached 3 solenoids to 1st, 3rd and 5th string of guitar.

Here is the connection.

As I did not have access to lab at all, I used ESP32 DevKitC as a board that controls 3 solenoids, one stepping motor and connect to Wifi network as a MQTT client.