MIDI Mod Wheel Using an Expression Pedal

A little while back, a friend asked me to help him with a keyboard problem he was having. He has one of those super cool Nord keyboards and the thing works great; except for the mod wheel. He's not sure how it happened but the thing just doesn't work. He also doesn't consider it important enough to open up the whole keyboard to see if it's fixable.

So, he asked me to make this little MIDI converter box for him. He already has a pedalboard with an unused expression pedal on it so this seemed like a great option.

Conceptually, this box is quite simple. Use some sort of microcontroller to take an analog reading of the foot pedal and convert that to a MIDI CC command to be sent to the Nord.

From that information, I created this. Bottom left is a TRS 1/4" jack I got off Amazon. It cost more than it should have but man is Prime shipping fantastic. Bottom right is the MIDI jack; from the same batch as my previous MIDI controller build.

The brain of the operation is a knockoff Arduino Nano from Elegoo (hey, it's cheap and I'm on a budget here) and also from the same batch as my previous controller. It's hard to see in this picture but, rather than soldering the Nano directly to the fantastic Perma-Proto Breadboard from Adafruit, it's actually sitting in some female pin headers who are concurrently soldered to the board below. This way, should something go wrong with this particular Nano, replacing it is an absolute breeze and nothing has to be moved around inside the box.

Speaking of the box, this is actually my first time using a DIY-intended enclosure. This particular one happens to be the Hammond 1591BSBK ABS Project Box. I also got it off Amazon. And, because I find electric drills to be loud and obnoxious, I used the drill below to handle my drilling needs. Absolutely in love with this thing for, well, its notable lack of obnoxious tendencies. And this project box being plastic, using it was far from difficult. I cut the notch for the USB on the Nano with a hacksaw.

You may notice that there are header pins soldered on to the white board in various locations and that there is nothing connected to them. This is because, when I initially created this 'motherboard', I was thinking about how I'd like to be able to remove it without disrupting the other components. This would be just like I did my previous MIDI controller. However, this one is FAR less complex than the previous one so I opted to just directly solder the wires instead. Saved a bit of time and is a sturdier connection anyway.

The motherboard is connected to the box through the two holes already in the Perma-Proto board and connected to some very short standoffs. You can see the screws for those standoffs outside of the box in the completed pictures a little further down this page.

Now done with hardware, I had to move on to the software. Full disclosure: I am abysmal at software. I get it, I just really don't like it. So, I was thrilled to find a fellow named Travis Thatcher who had created a similar project and was kind enough to share his program on GitHub. I'll link that project here. Much thanks and credit to him for that.

This was my test setup while messing around with software. A short TRS patch cable into another TRS jack soldered to a pot. Worked well enough and mirrors pretty perfectly the functional application of the whole thing.

You'll notice also that the thing is powered off of the USB port on the Nano. This is actually my only gripe against the MIDI protocol as, being a closed current loop, I can't utilize its 5 Volts to power little peripherals like this. I find this unfortunate as it would be incredible for my friend to not need an extra plug just to run this thing. If they were ever to update the MIDI protocol, this would be my only suggestion.

I'll add a picture of the box on his pedalboard once I have it but, until then, that's about it. Pretty easy project and cost less than $30 in materials, so that's cool.