A longer time ago I had bought an Edirol PC-50 MIDI keyboard, to be able to connect to some synthesizer programs on my computer:

Edirol Midi Keyboard Controller PC-5020091011_125230_0474cra
Edirol Midi Keyboard Controller PC-50
Edirol Midi Keyboard Controller PC-50

Now it would be interesting to be able to also connect it to my TTSH. For that I would need some MIDI-to-CV interface. At https://midisizer.com/midi2cv-mk2/ I found a nice little PCB design, called Midi2CV. It seemed to fit to the TTSH. I have ordered the PCB, and the needed components at Mouser. The Mouser components arrived first. As usual a lot of little plastic bags:

Midi2CV: The Electronic Components Delivery from Mouser20160114_204339_8618r
Midi2CV: The Electronic Components Delivery from Mouser
The package contents.
Midi2CV: The Electronic Components Delivery from Mouser

The delivery of the Midi2CV PCB and pre-programmed ATMega328p microcontroller took a little longer. It left the US quite fast, but customs in Germany took about two weeks.

Midi2CV: The Circuit Board20160131_142834_8621c
Midi2CV: The Circuit Board
Ordered and delivered from https://midisizer.com/midi2cv-mk2 . A few parts installed already.
Midi2CV: The Circuit Board

One component, the LT1021N precision reference, was not available at Mouser. I have ordered it, together with some other things, at Conrad. Then I could build up and test the Midi2CV:

Midi2CV: Circuit Board with All Components Installed20160207_174629_8633c
Midi2CV: Circuit Board with All Components Installed
The white chip is the 6N137 optocoupler.
Midi2CV: Circuit Board with All Components Installed

Temporary connection to the TTSH and PC-50 keyboard showed that the Midi2CV is correctly working.

There's just one thing I needed to reprogram on the Midi2CV: The strobe (or trigger) signal by default was inverted. Meaning, it triggered down from +10V. The TTSH requires a trigger signal going up from 0V. Changing was not difficult and possible by uploading an according Sysex file to the Midi2CV. The Midi2CV website provides this information. In order to do so from my computer, the PC-50 keyboard can be set into a mode where the MIDI signal received though USB gets passed on to the real MIDI output. This way it was possible to connect my computer to the Midi2CV. I used the Simple Sysexxer (note: page doesn't exist anymore) utility under Linux to upload the Sysex file.

Next I worked on a front panel for the Midi2CV, to be able to add it as extension module to the TTSH Case I'm building. That was easier said than done.

I'm using an aluminum L-shaped profile and designed the panel layout with QCAD. Jacks & Co. are mounted on perfboard. In QCAD I'm using a 2.54mm grid to align the panel holes to the perfboard. A temporary paper printout helped to locate the positions of the holes.

Midi2CV: Front Panel Preparation20160213_164314_8652cr
Midi2CV: Front Panel Preparation
Paper template to center the holes.
Midi2CV: Front Panel Preparation

Midi2CV: Front Panel Preparation20160213_164420_8653cr
Midi2CV: Front Panel Preparation
Connector board.
Midi2CV: Front Panel Preparation

Midi2CV: Front Panel Preparation20160213_192651_8654cr
Midi2CV: Front Panel Preparation
Front view of panel and connector board mounted together.
The aluminum got quite scratched during the drilling of the holes.
Unfortunately the lower big hole for the DIN plug got decentered.
Midi2CV: Front Panel Preparation

Midi2CV: Front Panel Preparation20160213_192736_8655c
Midi2CV: Front Panel Preparation
Top view of panel and connector board mounted together.
Midi2CV: Front Panel Preparation

That didn't work out as good as I hoped. I'm missing some good tools to make big holes in a better way. But I have added an aluminum-like adhesive printout that hides at least part of the “damage”:

Midi2CV: Front Panel Preparation20160213_215458_8656cr
Midi2CV: Front Panel Preparation
Aluminum-like printout with text and symbols.
Midi2CV: Front Panel Preparation

Midi2CV: Front Panel Preparation20160213_224101_8657cr
Midi2CV: Front Panel Preparation
Panel completed.
This didn't quite work out as perfect as wanted.
Midi2CV: Front Panel Preparation

From left to right the panel offers:

  • Three inputs to override the CV, gate and trigger connections to the TTSH.
  • A +5V connector to feed the MIDI keyboard (through a modified USB cable). This is internally connected to the +5V part of the power supply I'm using.
  • The MIDI-in and midi-thru/-out connections to and from the Midi2CV.
  • The MIDI-in and gate LEDs, and the learn button of the Midi2CV.
  • The four CV and four gate connections from the Midi2CV.

I have set up to use the monophonic connections, where CV 1 to 4 represent note, velocity, pitch band and control. Gate 1 to 4 represent gate, strobe, start and clock. Note, gate and strobe (trigger) are internally connected to the TTSH through the input override jacks.

Then I could build the Midi2CV panel into the TTSH case:

Midi2CV: Front Panel Preparation20160213_224334_8658cr
Midi2CV: Front Panel Preparation
Midi2CV: Front Panel Preparation

Internally the Midi2CV PCB is mounted behind the panel using two thin aluminum bars:

Midi2CV: PCB Mounted to Front Panel20160220_211811_8659c
Midi2CV: PCB Mounted to Front Panel
Midi2CV: PCB Mounted to Front Panel

When looking carefully, it can be recognized in the above picture that I have caused a shortcut with the mounting screw in the top-left corner. With that the Midi2CV didn't work after first time mounting into the case. I only noticed when unmounting again. The shortcut was between ground and the resistor connecting to the reset input of the ATMega328p microcontroller. Luckily, so no damage caused. Using a smaller screw helped.

Midi2CV: PCB with Front Panel inside Case20160220_212437_8662cr
Midi2CV: PCB with Front Panel inside Case
Midi2CV: PCB with Front Panel inside Case

Now the Midi2CV and TTSH work nicely together. The Midi2CV velocity, pitch band and control outputs correctly follow the PC-50 MIDI keyboard's key velocity, pitch bend and modulation lever respectively.

Midi2CV: Up and Running, Connecting Midi Keyboard to TTSH20160225_215456_8663
Midi2CV: Up and Running, Connecting Midi Keyboard to TTSH
Midi2CV: Up and Running, Connecting Midi Keyboard to TTSH


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