Larry Cotton’s MIDI Robot Marimba: Update

Over 4 years since Larry Cotton’s “player marimba” was featured in Make and subsequently retrofitted for MIDI using MD24 MIDI decoders, the instrument is still going strong. Larry recently updated the drive circuitry, replacing the original relays with NPN Darlington transistors to drive the mallet solenoids. Video of the marimba in action can be found here and here.

MIDIMarimbaLarry writes:

My MIDI Marimba (which uses 2 of your MD-24’s) is 90% refurbed.

The MD24’s work perfectly, and are more than capable of triggering the TIP-120’s, a vast improvement over relays, etc.

I also added RCA plugs and jacks to the mallets, for easy servicing and assembly/disassembly.

The first pic shows early stages of the new wiring. The power supply’s pretty beefy for the solenoids, with adjustable output around 12V, and 5V for the MD24’s.

The second pic was taken just before all the wires were stuffed in and the plexiglass cover installed.

The third pic shows it all buttoned up. That’s an iRig Keys keyboard on the floor, and an ancient Gateway laptop running Cakewalk software. I’m also using an M-Audio Uno to deliver MIDI to the MD24’s.

The wonderful little iRig Keys allows the marimba to be recorded and played manually. Kids love it.



MIDIMarimbaSystemThe picture below shows an initial test of the MD24 and TIP120 driving one of the marimba’s solenoids. Video here.




Dubi’s MIDI Accordion

MIDI CPU user Dubi from Israel has completed an extensive MIDI conversion of an Iorio Accorgan. He writes:

I have been using Iorio Syntara as the model for you. The Syntara used to be an Accorgan –


I removed the electronics:


but I used the switches:


There are 41 notes on the right side of the accordion , so my choice was for 6 inputs (0 to 5) and 7 outputs (6 to 12). There is a need to modify the existing switch circuit to have the configuration of 6 by 7:



I installed the midi controller , and midi connector and of course power connector of 12 Volt.



In order to have a good looking accordion , I designed a new panel .. And installed it.


The right switches are connected 6 x 7 , first 0 to 5 are the inputs and 6 to 12 are the outputs of the right side.

The sysex table for the right side:

// Fixed Header, Configuration Layer 0
F0 00 01 5D 04 01 00

// Control Terminal 0-5: Data Only
00 00 7F 00 00 00
00 01 7F 00 00 00
01 00 7F 00 00 00
01 01 7F 00 00 00
02 00 7F 00 00 00
02 01 7F 00 00 00
03 00 7F 00 00 00
03 01 7F 00 00 00
04 00 7F 00 00 00
04 01 7F 00 00 00
05 00 7F 00 00 00
05 01 7F 00 00 00

// TREBELE Section
// CT 6 Matrix Select Output: Data Register 00h, note number 53-58
06 00 2C 01 35 00
// CT 7 Matrix Select Output: Data Register 00h, note numbers 59-64
07 00 2C 01 3B 00

// CT 8 Matrix Select Output: Data Register 00h, note numbers 65-70
08 00 2C 01 41 00
// CT 9 Matrix Select Output: Data Register 00h, note numbers 71-76
09 00 2C 01 47 00
// CT 10 Matrix Select Output: Data Register 00h, note numbers 77-82
0A 00 2C 01 4D 00
// CT 11 Matrix Select Output: Data Register 00h, note numbers 83-88
0B 00 2C 01 53 00
// CT 12 Matrix Select Output: Data Register 00h, note numbers 89-94
0C 00 2C 01 59 0A

// BASS Section
// CT 13 Matrix Select Output: Data Register 00h, note number 36-41
0D 00 2C 03 24 00
// CT 14 Matrix Select Output: Data Register 00h, note number 42-47
0E 00 2C 03 2A 00

// CHORD Section
0F 00 2C 02 3C 00
// CT 15 Matrix Select Output: Data Register 00h, note number 60-65
10 00 2C 02 42 00
// CT 16 Matrix Select Output: Data Register 00h, note number 66-71

// Fixed Footer

// Global Volume
F0 00 01 5D 04 02

The left switch circuit has to be modified as well to 6 input and 4 outputs:




In the left side there are 12 notes of the Bass section and 12 notes of the Chords section. Each 12 notes has to have it’s own Matrix. so I used the same 6 inputs and 2 outputs for the Bass side and 2 for the Chord section:


Once again In1 to In6 are connected to 0 to 5 and Out 1 & Out 2 to 13 and 14 of the midi controller. The same applied to the Chord section , i.e. inputs are the same conneted to 0 to 5 and the output of the Chords to 15 and 16.

The Bass section is straight forward as in the table above. However , in many instruments as well as in the accordion Chords can be played inversed. and in order to get the correct Chord range as well as match the Acoustic part of the accordion, it is advised to change the above

Chord table, use deferent location in the Note space and use a conversion map to correct for the “Chord range”. I used location 18 to 23 and changed the Note map to produce the “Nice Chord Range”:

F0 00 01 5D 04 05
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
10 11 12 13 14 15 16 17 30 31 3E 3F 40 41 42 37
38 39 3A 3B 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F
30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F
40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F
60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6F
70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 6E 7F

There have been few “glitches” had to go through Factory defaults after upgrading to version 1.4 and also had to change the “Global Velocity” Parameter (seems to be deferent in the beta version. Frankly, I have not done yet a complete research . I was satisfied with the results. Works like charm.



Galanti Praeludium II console MIDI retrofit

Highly Liquid Forum user Jim U recently completed a MIDI conversion of a Galanti Praeludium II organ console for use with Hauptwerk virtual organ software. Three MIDI CPU units generate MIDI output from manuals, stops and pedals. Four MD24 units drive various LED indicators on the console. Additional project discussion can be found at The Organ Forum.




Highly Liquid user profile: Pastel Fractal

Chicago-based artist Alexander DeGraaf employs several UMR2 and MSA-T boards for his ongoing project Pastel Fractal. Alex uses MIDI control for robotics and live audience participation in addition to more traditional sequencing and synthesis functions.


Alex writes:

I have three sampling keyboards into which I have installed UMRs: two Yamaha VSS-30s and one Casio SK-8.  I use different samples on the keyboards for different compositions such as: my singing voice, a dog bark (sampled from SK-5), a TR-808 clap, a Doc Watson banjo riff, a Chet Atkins guitar riff, and some scatting sounds.

In my installation sculptures, I’ve used as many as two MSA-T MIDI Decoders to turn my MIDI note messages into voltage pulses for as many as fourteen small 24V solenoid motors. I’ve engineered these motors to reset immediately after being triggered, and I’ve connected them in various ways to percussive elements within the sculptures. In this way, I am able to MIDI-sequence robotic percussion strikes and sounds in sync with my compositions that are otherwise played by more conventional MIDI sound engines such as synthesizers, keyboards, and drum machines. The robotic percussive elements within the sculpture each provide a unique source from which sounds stimulate the inhabitant of the sculpture. I provide additional sound sources – besides robotic percussions and the main P.A. – by attaching small speakers to individual keyboards and drum machines so they may be hung around the sculpture or handed out to the inhabitants to pass and move about. Thus, inhabitants of the sculpture – also known as members of the audience – can contribute to the composition during a performance with these floating pieces of hardware by engaging buttons or keys within their reach.

More from Pastel Fractal can be found at Vimeo, Soundcloud, and Facebook.

Vintage Hammond drawbars as MIDI controller for Nord Electro 3

Highly Liquid Forum user cjfox rehoused a set of Hammond drawbars and replaced the original resistor wires with slide pots. Then he used a MIDI CPU to convert the drawbars into a MIDI controller for use with his Nord Electro 3.  The MIDI CPU configuration is posted in the project’s forum thread.