Recollections

Recollections is a voltage memory module for Eurorack modular synthesizer systems offering 8 output channels across 16 presets, 16 banks and 16 modules for a total of 32,768 recallable voltages. It may be quickly reconfigured to function as a controller, a sequencer, a track-and-hold, a sample-and-hold, a random voltage generator, or all of these at the same time and in conjunction with each other. The data is stored on an SD card for later recall, and the storage files are easy to read and edit.

Demo Videos

Please see the Octovolt YouTube channel.

User Manual

A user manual may be found here: https://docs.google.com/document/d/1RPAPcG-z0c8NyQLCnBXKaI8nIInMwIazlKRt4L1SheU

Project Status

Recollections is currently a work in progress, with a goal date of December 31, 2024. The code was originally written for Teensy 3.6, then for Teensy 4.1, but due to the high cost of those microcontroller boards, I chose to switch to the Raspberry Pi Pico. The Pico is about $30 cheaper, but it's slower, most notably when reading and writing to the SD Card. On the plus side, beyond the cheaper price, the Pico supports 12-bit data on its ADC, so the resolution of the voltages is truly 4096 steps rather than the 1024 steps of Teensy's 10-bit ADC. I will continue to make Teensy-based PCB/panel sets available, however, for the hard core DIYer who wants faster SD Card writes and does not care about the various benefits of the Pico. Please contact me if you are interested in using a Teensy 3.6 or 4.1. I will also offer both PCB/panel sets and full kits for the Pico. While the kits are more expensive than the PCB/panel sets, they are much more convenient and avoid the shipping costs that would be incurred by ordering parts from multiple suppliers.

The main blocking issue at the moment is the external SD card I am using with the Pico. The reads are working, but not the writes. As soon as this problem is solved, Recollections will be released and kits will be available.

Compiling the Code

Across all platforms, I use the Arduino IDE to compile the code. Sometimes I wish I was using pure C++ and CMake, but the many libraries offered by the Arduino ecosystem has kept me from doing this. Maybe someday.

How to Compile for RP2040 / Raspberry Pi Pico

Because this code was originally writing for Teensy 3.6 and Teensy 4.1, I decided to use the arduino-pico library to enable it for the Pico. Please use this to update your boards manager in the Arduino IDE prior to compiling so that Raspberry Pi Pico becomes a possible compilation target.

Additionally, the following hack is required:

• Update files related to StreamUtils to include <api/String.h> instead of <WString.h>. Please see SDCard.h for details.

How to Compile for Teensy

Teensy has the benefits of increased speed, an onboard SD card reader and true random number generation. Unfortunately, it also has a 10-bit ADC rather than Pico's 12-bit, and it is about $25 USD more than the Pico. For this reason, the Pico is now the main target of this project. However, you might care about the aforementioned benefits, or you might simply have a Teensy lying around waiting for a project.

The following hacks are required for Teensy:

• Teensy 3.6 requires the i2c_t3 library to be included instead of the more standard Wire library, so a few external libraries need to be changed to include i2c_t3 instead. Please see details at the top of Recollections.ino. This is not an issue for Teensy 4.1, which can use Wire instead.
• The SD library used for Teensy must be the Teensy-specific one. You may need to rename other SD.h files to something like SD-disabled.h to get the compiler to use the correct library.

Additional Dependencies

In addition to arduino-pico and api/String for Pico, or i2c_t3 for Teensy 3.6, Recollections also depends on the following non-core libraries across all platforms:

• Adafruit_MCP4728
• Adafruit_Seesaw
• ArduinoJson
• StackString
• StreamUtils

Contributing

Pull requests are absolutely welcome, but we should probably discuss your idea before you expect to merge it into the repo -- maybe even before you write the code. In terms of formatting, I do expect strict indenting with 2 spaces, not tabs. Otherwise, please see the code for the various conventions I use. Most are standard, a few are idiosyncratic, but I want to keep the code consistent.

My priorities for future improvements:

• Unit tests. I'm ashamed at the lack of tests. Pull requests with tests will be the most appreciated.
• I'm very interested in using both MIDI and i2c to control the module. MIDI would require an expansion module, but I believe the code can be written for i2c and a future MIDI expansion module would simply translate MIDI into i2c commands.
• I'd also like to leverage i2c to send and receive messages between more than one Recollections module to create bigger sequencers. That is, I envision two linked Recollections modules creating a 32-step sequencer, or even four modules creating a 64-step sequencer.
• I sometimes wonder how I might create polychronic sequences on the different output channels. That is, it would be great to have a 16-step sequence on channel 1, an 8-step sequence on channel 2, and a 5-step sequence on channel 3. However, this could introduce a lot of complexity not only within the UI, but also within the data itself.

Thanks

Thanks for taking a look at this project. It's been a labor of love since I first conceived of the idea on my way to Europe in June of 2021. Unfortunately, I came down with covid while in London, so to take my mind off the horrible cough I started writing the code for Recollections. I designed the first version of the circuit and laid out the PCB when I got back to California, but many iterations have happened since then.