I am starting to get a better sense for what my first Eurotrack module might look like. It would be 25HP wide (5 inches), and its faceplate would be built around an iPod Touch. The former would be used as a display, as a touch-enabled control, and as a powerful computing unit for advanced digital signal processing. It would be interfaced to a built-in Arduino core over USB.
This module would provide 8 polyphonic channels. Each channel would have four 3.5mm jacks (input, output, two voltage controls) and one or two potentiometers. Each channel would also have its own internal breadboard area. In there, any combination of components could be used, with up to 16 mixed signal pins per channel. The breadboard components of a channel would be connected to the channel’s faceplate controls via a dedicated AD75019 analog crosspoint switch. Additionally, two analog crosspoint switches would be used to connect to the Arduino core.
Each analog potentiometer would be connected to four AD5254 digital potentiometers with 256-position resolution and four resistance ranges (1 kΩ, 10 kΩ, 50 kΩ, 100 kΩ). Four analog potentiometers would be connected to the same four sets of digital potentiometers, for a total of thirty-two digital potentiometers housed within eight chips. This would allow the user to select the desired resistance range, while being able to set the potentiometer’s position either manually via the analog potentiometer, digitally via the Arduino core, or modularly via voltage control.
One of the main benefits of using an iPod Touch in the middle section of the module would be to provide a graphical oscilloscope for every of the eight channels (4 on top, 4 at the bottom). This feature alone would make my module more cost effective than buying a full set of four dual-channel Eurorack oscilloscope modules from Jones O’Tool. An AD7606 analog to digital converter could be used for this purpose.
From a user interface standpoint, the iPod Touch would be used to configure the connections between faceplate controls and internal components (both breadboard components and Arduino shields). These connections would be defined using a simple CSV file that could be downloaded from the cloud via the iPod’s WiFi interface. As a result, the module would not have to be physically connected to an external laptop for development purposes, even though this would be supported as well via a USB connector.
Software development for the module would be done either as an iOS application, as an Arduino application, or both. The module would not come with a built-in Arduino core, allowing users to select the one that would be best suited to their application. The module would also support the addition of Arduino shields internally, with a depth limit defined by the Eurorack cabinet being used to house the module. This analog shield by Digilent would be a good one.
Here is a breakdown of the main components:
- 1× iPod Touch, $199
- 10 × AD75019 analog crosspoint switches, $200
- 8 × AD5254 digital potentiometers, $24
- 1 × AD7606 analog to digital converter, $20
- 1 × Arduino Uno, $25
- Faceplate with knobs and connectors, $100
- Printed circuit boards, $100
- Breadboard, $100
That woud lead to $768, which means that such a module could retail just north of $1,000. This would make it one of the most expensive Eurorack modules out there, but also one of the most powerful and versatile.
Time to order some evaluation boards…