The Stepchild

Welcome to the github page for the Stepchild MIDI instrument project, an open source generative MIDI instrument. The Stepchild is a portable step-sequencer and experimental songwriting tool built around the Pi Pico and a love for drum sequencing, and it's open source because building your own is cool as fuck.

Open Source

The Stepchild is an open source project which means you can contribute to, remix, create your own version of, and copy the hardware & software designs that are a part of the project, with some restrictions. The Stepchild's physical design is released under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, which is a non-commercial license, but get in touch with the project if you'd like to talk about selling your own version of the Stepchild or something Stephild related! The Stepchild's software is licensed under the GNU General Public License v3.0 and can be found in the code folder.

Project Overview

The Stepchild contains a flexible step-sequencer, CC automation and envelope data, experimental realtime MIDI instruments, a sequence editor including note FX, an onboard filesystem for sharing sequences, an arpeggiator, a live MIDI looper, CV output (natively +3.3V, eurorack power supply required for +12V), a Program Change sequencer, a MIDI console for debugging MIDI setups, and flexible port routing for using the Stepchild as a MIDI interface: 4 MIDI outputs and 1 MIDI input, each of which is accessible through a 3.5mm TRS jack (a headphone jack) and a classic MIDI DIN jack, and one input/output port via USB MIDI.

Hardware

The Stepchild's current hardware version is v0.9.2. To build one, you will need:

PCB

• Main, CV, and step sequencer breakout circuit boards
• All the components from the BOM
• MIDI Breakout Board (Rack Mount Only)
• Eurorack Face Plate (Rack Mount Only)

Case

• Top & Bottom Shell
• Battery & Eurorack compartment clips
• Silkscreen Graphics

Some Notes!

All the Stepchild case components were originally designed to be made with an SLA printer. The Stepchildren I'm building are made with resin printed cases, though, but all the pieces can be made on an SLA printer.

Software

The Stepchild is powered by the onboard Raspberry Pi Pico which can be flashed using the Arduino IDE or Platform.io/VS Code. The official Stepchild software is ChildOS.

ChildOS has a powerful sequencer, looper, and Automation function generator, as well as 9 instruments and FX. There are a total of 16 Instrument slots and 24 FX slots that can be swapped with user-created code written in C++ (See documentation on creating custom instruments for a tutorial).

Main Features:

1. A graphical interface
2. A step sequencer
3. A note editor
4. A track editor
5. A CC Automation ("Autotrack") sequencer
6. A customizeable looper, with up to 256 loops of any length
7. An onboard file system
8. A randomizer
9. An arpeggiator
10. A console to view incoming MIDI data
11. A customizeable clock, integrated with Autotracks for weird timing

Instruments & FX:

1. Joystick-to-CC -- Use the Stepchild's joystick as a MIDI controller
2. Rain -- Generate ambient notes
3. Rattlesnake -- Output notes wth varying speed
4. Knobs -- Use the Stepchild's encoders as MIDI controllers
5. Quantizer
6. Humanizer
7. Strum
8. Echo
9. Reverse

Filesystem & ChildOS Interface

The Stepchild uses LittleFS to set aside 1MB of the Pico's onboard flash memory for storing songs and sequences. ChildOS Interface is a standalone Java app that lets you download saved files from the Stepchild and convert .child files into .MIDI files, for playback in a DAW. Additionally, .child files from one Stepchild can be shared between Stepchild(ren).

Contributors & Thank You's

The Stepchild's hardware and software is created using the hard work of a lot of other people. A special thanks to the creators and maintainers of the following projects that ChildOS uses:

• The EuroPi Project started by Allen Synthesis, specifically for providing the design for the analog CV out circuit
• FortySevenEffect's MIDI Library
• TinyUSB
• Adafruit GFX Library and the Adafruit SSD1306 Library
• LittleFS project
• Earle Philhower's Arduino-Pico Core
• KiCad <3 & Blender

Please see the license.txt doc for full credits.

Version History

Software

Hardware

v0.9

6/7/24

• Printable clip covers for Eurorack IDC jack and battery compartments on bottom shell
• New graphics & net labels on the PCB design
• Prototype version of switchable +3.3v<-->+12v circuit to swap between Eurorack power and Battery power
• +12v indicator LED
• Centered OLED screen on PCB