Computer Musician, Programmer, Hardware Hacker

Here are some things I’ve observed while developing the tabulaRasa and the USB-Octomod. Both projects are open-source hardware/software packages for use in modular synthesizers.

For me, the process divides up into three stages: design, funding, and production. I’ll cover each stage in a separate post.

Design

Make sure to spend plenty of time brainstorming, prototyping, scrapping, and remaking your project.

You want to explore as many angles as possible. Often a redesign or code rewrite will make implementing new features easier, or allow you to optimize some aspect of the design. Both the Octomod and the tabulaRasa went through multiple stages of sketching, prototyping, pcb design (and fabrication) before I decided they were done.

Aim to use common, versatile components.

You don’t want to use a single-supplier component in a design, unless there is no other option. The Octomod uses a Teensy 2.0 microcontroller unit which is available from only one source. Within a few days of announcing the availability of PCBs, the Teensy 2.0 went out of stock, and stayed that way for months. Besides limiting the usefulness of the PCBs, this left me fielding questions about the availability of a product over which I had no control. Some people are experiencing a similar issue with the SD card socket used in the tabulaRasa. Since the part is available from Sparkfun, I assumed it would be relatively simple for people to get. However, I didn’t consider that shipping to European countries from Sparkfun is either expensive or impossible. (Not sure which it is, I just know I got some questions about alternate sources.)

Using a minimal amount of components is also an advantage.

My initial designs for the tabulaRasa used a separate DAC chip, interfaced to the mcu through SPI. Although this theoretically provides for much higher bit resolution, most DACs require 16 or more bits to be transmitted per sample. The additional chip also added significant cost to the project. I instead used a simple PWM DAC, using an RC lowpass filter to smooth out the built-in PWM output of the ATmega. Simple, cheap, and still of a high-enough quality for my needs.

Open-source is an asset.

Many of the technical questions I received (usually related to compilation or misunderstanding of OSC) were easily solved because users could send me the exact error messages or line numbers they received. (On the other hand, asking users to compile their own code also led to confusion. I had a few people try to compile Arduino code in Processing, and vice-versa.)

More to come on how I raised money for construction on Kickstarter, and my thoughts on the manufacturing process.

Here's the first prototype of my tabulaRasa wavetable oscillator module

Making progress on the tabulaRasa hardware – ordered the second prototypes from dorkbotpdx today. More soon.

The box the Ohm came in.

I recently found out that you can get a “graveyard” Ohm MIDI controller from Livid Instruments for $30. This is a defective unit that they couldn’t sell. They’re secretive about what’s wrong with the units, and there’s little to no documentation available, but I thought it would be fun to attempt to rebuild one.

I also ordered a Ohm64 case, which is a wooden shell for the hardware. It’s not exactly the right size, but I thought I might be able to convert it to work with the Ohm Classic.

The circuit boards of the Ohm, as I received them.

You can see in the image above that the boards are a bit old, I had to rub some corrosion off – a bit of rubbing alcohol did the trick. The “double-checked” marking  on the back of the main board was reassuring. The loose wire beneath that main board was a bit scary, but it turned out the be a ground wire which connected the three panel boards to the main controller board.

In all, I received 4 boards – three, attached to the panel, which contained the pots, sliders, and buttons. These three connected to the fourth through a set of ribbon cables and power wires.

Note that these “graveyard” Ohms do not come with the MIDI/USB I/O board. I ended up having to order one separately. Extra shipping – be careful!

Main board, wired up for testing.

My next step was to somehow power the board – without the I/O board power circuitry – and test the controls. More on that later.