1V/oct CV/Pitch Keyboard controller

Building a CV Controller (Again)

Over the past few days, I've been playing with the idea of a 12-key CV keyboard. I've built other CV controllers before - including a mini repurposed keyboard segment atop a custom voltage divider circuit, and a fully-weird follow-up, complete with joystick. For my next foray into keyboard CV/Pitch controllers, I am revisiting the voltage divider approach.

Sketching out some basic voltage divider math.
Sketching out some basic voltage divider math.

Preliminary Specifications

The chief difference this time is: I'm actually understanding the required math a little better, so I'm trying a little more diligently. First, I sketched out my ideas (above) and did a little research. Then, experimentally, I started plugging resistor values into a spreadsheet (below) using a formula I found. I want to use the 1V/Octave method, and I have a custom power supply that delivers 4.5V (actually, about 4.23V, according to my measurement thereof).

Comparing ideal and practical resistor values.
Comparing ideal and practical resistor values.

Again, experimentally, I assumed that my "R1" could be a 1K resistor. I then calculated the appropriate "R2" values for my octave of notes. Then, I looked at the [common] resistor values in my hands at the moment, and I was able to theoretically get awfully close to the desired numbers - within 10 Ohms, most of the time.

Next, I'll run my whole plan through a circuit simulator.
Next, I'll run my whole plan through a circuit simulator.

A Variety of Tests in Progress

Next, I'm going to build the same circuit in EasyEDA's simulator, more or less as another (remarkably cool) check of my math. As you can see below, I have begun the preliminary layout of this idea on a protoboard. Alongside an array of serial resistors, I also include 12 diodes, a recycled DC power jack, and a recycled 3.5mm audio jack, which will convey the control voltage to other homemade devices.

Committing numbers and theory to a protoboard.
Committing numbers and theory to a protoboard.

Updates and Files Forthcoming

I'm still thinking about this prototype layout and the wiring and soldering that will be required - and so I might change a few things before burning everything into place. And I'm still very far from committing to a key/keyboard design. The only thing [I think] I know right now, is that these twelve horizontal rows of resistors are going to get me very close to what I am envisioning. I will post again on this project as it evolves, and I will eventually share my schematic and related files on the Junklopedia.

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