When we start to developing GHAMMY harm/pitch-shifter, we need solution to control it with pedal.
Just bought cheap and very nice midi Expression pedal (Nektar NX-P price: $19.99). But this pedal is MIDI and have 1/4″ Jack cable.

If you have some hardware in setup, just try to find any device with Expression input port. In my situation, I find that Novation Supernova II rack, include Expression input. Just connect it and work into Reason thru Midi channel from my UB Midi Interface. Just try to find Expression input in you Midi Keyboards and controllers, some hardware synths..

Not find in your setup Expression pedal Input??? Don’t worry! And there we start!

You can build very fast and easy your own:
a) Expression Pedal MIDI -> USB Converter
b) Add to this converter box some controllers.

When I start to search now to convert Midi Expression -> USB, I found some solutions, that have big price. But, ARDUINO (also for beginners) – is a real help. And now I think that every musician can customise own setup of controllers and converters.

What we need:
1. ARDUINO (that support MIDI library): DUE, Leonardo, Micro as example (UNO not support MIDIUSB library!!!). Its cheap (I bought Leonardo about $10).
2. Stereo Input 1/4 connector (stereo, because expression pedal have stereo jack)
3. Any box
4. Some needed controllers (if you interesting to add midi controller possibility to the box). Im personally add to small box: 2 Pots (linear b10k), knobs for them, 1 switch (ON-ON with triple pins). Of course you can use more controllers, include buttons, faders, pedal switchers, photoresists.. etc.
5. Some wires. Good to buy non-soldering wires with Mother/Father pins.
6. Soldering kit.

Idea based on DIY project created by KUASSA (simple converter for Expression pedal to USB port, that include SPDT switcher):
https://www.kuassa.com/diy-tutorial-how-to-build-arduino-based-expression-pedal-for-efektor-wf3607/

Im just add 2 POTs, and change 3PDT switcher to SPDT switcher. You can customise this project for own needs.

START BUILD:

1. ARDUINO: Im prefer for first project  LEONARDO version. Section “POWER” include 2 pins for our controllers: 5V and GND.
   All connected potentiometers (also Expression pedal input), faders – must be powered by 5V pin, and linked to the ground by GND pin.

   

2. Expression input:
   
   All you must do now with Expression pedal input, just set it to the box.
   You can use another type of 1/4 Input connector:
   

3.  Now we practice to add 2 pots for our box.

This is our small midi controller for own needs (Not need controllers? Go to section about Arduino IDE).. Or just add pots, buttons, faders, etc to your box.

Add 2 Pots (linear b10k). Pots have 3 pins (5V, GND and Signal line). Signal lines for two our pots at Arduino side – ANALOG IN (A1 and A2, because A0 already connected for Expression input). 5V and GND we also connects as previously in POWER section to 5V/GND. 

4. SWITСH: Im prefer small but usable SPDT switcher with 3 pins (its cheap). Later in the same way add buttons if you need. For swithchers, buttons – you must use at ARDUINO – DIGITAL (PWM) pins.

• Pin GND of switch connect to the DIGITAL PWM section: GND.
• Medium Pin of switch connect to the DIGITAL PWM section: 9
• Last pin  connect to the POWER section of Arduino (on Leonardo): 5V.

5.  If needed – add more pots (faders), may be buttons (like we add switch) in the same way.

6. Prepare your box. Drill holes, and fix switch, pots, Expression input. Box is ready!!!

ARDUINO! Its not hard and expensive. You can build with it own midi controller.

1. Download Arduino IDE (at macOS last version 1.8.12 – not work! Just download 1.8.10 for mac).
2. Connect your USB port of Arduino to PC/Mac
3. Go to the menu: SKETCH -> INCLUDE LIBRARY -> MANAGE LIBRARIES.. Add two libraries MIDI Library and MIDIUSB by search
   
   
4. Go in menu to the TOOLS -> BOARD -> select your board from the list
5. Go in menu to the TOOLS -> PORT -> select your port (by device name) from the list
6. Download sketch code here and open it from Arduino app. This file based on the KUASSA original file (Thank You KUASSA for this perfect idea!).
7. Press button “UPLOAD”. When finished, ARDUINO write to you “Done uploading”.
   

8. If your Arduino include reset button, press it. Disconnect your ARDUINO (your ready box) and reconnect usb cable.
9. Open your Reason app and test your box! Click at any needed device element “Edit Remote override mapping”, check “Learn”, and move any knob, button, switch or your Expression pedal, and it must be recognised under name of your ARDUINO model:

That is all!!! Now you can customise your box as midi controller for personal needs. Its now not just a Expression midi -> usb converter. Its now midi controller.

Personal thank you for KUASSA, ARDUINO community and anybody who build own controller/converter.

WE HIGLY RECOMMEND TO YOU USE ANY EXTERNAL EXPRESSION MIDI PEDAL WITH OUR GHAMMY HARM/PITCH SHIFTER.

Foot controller + few knobs, buttons or switchs really helpful in situations when you already have midi controllers.