MPA open-sourced, on sale

The complete design (PCB, bill of materials, firmware source code) for the MPA MIDI decoder has been posted under the Creative Commons Attribution-ShareAlike license. The source files can be found at the MPA support forum.

The MPA has been placed on sale at the Highly Liquid Store and will be discontinued after remaining inventory has been depleted.

The MPA (MIDI potentiometer array) is a general-purpose MIDI decoder with 8 independent 5V logic outputs and 4 independent digital potentiometer outputs.


Disappearing Cowboy’s Automated M.O.T. Stage Rig

John Erik King, the sole instrumentalist of Disappearing Cowboy, has created the “Minimalist Organic Tech” stage rig, an integrated system that includes guitar effects and amplification, bass, synthesis, vocal processing, and robot drums. Scripted MIDI messaging provides “scene” control, freeing King to simultaneously perform live guitar, bass, and synth.

M.O.T. Minimalist Organic Tech from Disappearing Cowboy on Vimeo.

King’s description of the system:

  • kick, one actuator.
  • snare, one actuator.
  • ride cymbal, two actuators to account for the high volume of repetitive patterns typically played on cymbals.
  • toms, two actuators, again to account for quarter/sixteenth note repetition.
  • crash, one actuator with a very long throw to really smack the crash cymbal so it stands out.
 M.O.T. Rig
  • bass, mute, and distortion control. (big muff)
  • guitar, Moog LP ladder filter into an eventide stereo digital delay. The stereo output then goes to two different amps with independent mutes.
  • synth, only one string goes to a Roland GR-30, which has its own mute as well.
M.O.T. Batar
  • has three outputs. Bass, guitar, and synth.
  • tuning E (bass string), E,B,E,B,E. (five other strings)
  • top three strings are attached to a modified Bigsby tremolo which creates a relative detune effect.
Because everything is controlled by MIDI, we can shift scenes and tempos for each song, or even in between songs. The vocal delays and guitar delays are in perfect sync with the tempo which the drums precisely adhere to. If the tempo is at 135, everything is locked at 135.
I originally controlled everything with a laptop, but found a karaoke device that plays back MIDI files to use instead.
All the different scenes and transitions are triggered automatically. And the entire set is set up like a playlist. We hit one button and the entire show plays without any foot controllers or input like that of any kind. It’s all automated, with the exception of playing the instrument, of course.


The rig employs two Highly Liquid MSA-P MIDI decoders to trigger drums, route audio signals, switch amplification channels and control effects.  An MPA MIDI decoder is used to automate control of the Moog ladder filter.

The new Disappearing Cowboy album, Revolute, is available from every major online music distribution platform including Amazon, iTunes, Soundcloud, and several others.


MPA Update

The MPA MIDI Decoder (potentiometer and logic output) hardware is being updated.  The improved design features simplified assembly, smaller footprint and easier-to-read I/O labels.  The new boards will be available in early June.

User Project Roundup, Part 10

Daren Ager’s modular drum demo, using an MPA MIDI Decoder as an interface between a Machinedrum and modular gear:

Ronin Otter’s UMR / Casio SK-1 installation how-to video (also see Nomeist’s UMR mini-review):

MIDI2600 / Synthcart / Atari 2600 demo video by The Longhorn Engineer (also see this MIDI2600-External enclosure discussion):

Spunkytoofer’s latest noise machine which includes an MSA-R for MIDI control (lots of other devices here):

Stylinghead’s photos of a clever CS01-MIDI internal install by Billy Neenos:

A Boss DR-110 / MD24 MIDI retrofit project from Darren at MakerSpace, Wellington, New Zealand:

MPA Firmware Update (V1.4)

MPA Firmware Version 1.4 is now available.  The new features are:

  • User configurable power-up states for all outputs
  • CC “on/off” mode for logic outputs
  • “Any note” modes for logic outputs (output responds to any note number)
  • Device is pre-configured with a “factory default” configuration

Complete details can be found in the firmware user manual, linked at the product page.

MIDI SysEx Tools


Many MIDI-enabled devices can be configured via the MIDI interface. This is typically accomplished via a special type of message called “System Exclusive” or “SysEx.”A device’s SysEx message format is specified by the vendor. For Highly Liquid products, please see each product’s documentation for SysEx message formats.

SysEx Messages as Files

SysEx messages are typically stored in one of two file formats:

  • A plain text file (.txt)
  • A raw hex file (.syx)

Below is a simple 7-byte SysEx message with example file representations.

Message contents (hex): F0 00 01 5D 02 00 F7

Corresponding files:

Text files can be edited using any basic text editor such as Notepad or vi. Raw hex files require the use of a “hex editor.”

Note: text can now be converted to raw hex .syx file here.

Sending SysEx Messages from a Computer

A SysEx message can be sent from any computer with an installed MIDI interface.Many sequencing programs have built-in SysEx functionality. There are also stand-alone SysEx applications available for free download.Recommended stand-alone SysEx programs:

  • SendSX (Windows): Stores & loads SysEx messages as text files. SysEx data can also be manually entered directly into the application.
  • SysEx Librarian (Mac): Stores & loads SysEx messages as raw hex (.syx) files. Use this tool to convert your code to a .syx file. You can also edit the .syx file using a hex editor like HexEdit.

Firmware Updates

Firmware has been updated for the MIDISpeak, MIDI2600, MPA, SKM and UMR kits. The updates address an incompatibility with some MIDI controllers & sequencers which can cause an imperfect note response. The recent MSA firmware update also addresses this issue.

Products purchased after February 1, 2008 include the updated firmware. Microcontroller ICs from earlier products may be returned for a free upgrade. Please send email for additional information.