Chainable Arduino Sequencer

The Eurorack Sequencer is a straightforward, flexible 8-step sequencer designed around the Arduino Nano. It offers a hands-on approach to pattern creation with plenty of CV control options and modular expandability. Multiple units can be chained for longer sequences, and since the firmware is open-source, you can easily tweak or extend the functionality to suit your setup.

Perfect companion for the Quantize & Hold module.

Key Specs

#

• 8-step analog sequencer
• Unquantized CV output
• Arduino-based open-source firmware
• Front-panel controls for rate, step count, gate length, and glide
• CV inputs for rate, step count, and gate length
• Clock input/output for syncing with other gear
• Gate output and reset input
• Extension port
• Supports daisy-chaining for longer sequences
• Output voltage range: 0–5V
• Width: 18HP

How It Works

#

The sequencer operates by cycling through eight digital output pins on the Arduino Nano. Each output is connected to a potentiometer, which acts as a voltage divider to set the control voltage for that step. These voltages are summed and sent to the CV output. A glide control adjusts the transition time between steps, allowing smooth slides instead of abrupt jumps.

The sequence speed is set with the rate knob and can also be modulated via CV input. The step count control determines how many steps are active in the sequence (from 1 to 8), and this parameter is also CV-controllable for dynamic pattern changes.

The gate length control defines the duration of each step’s gate signal — useful for triggering envelopes or other time-based modulation. Gate length can also be influenced by an external CV.

Additional inputs and outputs provide flexible synchronization:

• Reset input restarts the sequence from the first step.
• Clock input allows external timing control.
• Clock output sends the internal clock signal for syncing other modules.

Video

#

Assembly

#

The build is straightforward and beginner-friendly. The module uses only through-hole components, making it easy to solder and assemble. The design is split into two PCBs: the front panel and the main circuit board.

Start by soldering all components onto the main board, beginning with the lowest-profile parts (such as diodes and resistors) and working your way up to larger components. Leave the LEDs, jacks, and potentiometers for last.

If you don’t plan to use the extension port or link mode, you can skip the corresponding connectors. Before soldering the LEDs, jacks, and potentiometers, mount them to the front panel to ensure proper alignment and a clean fit.

Each component location is clearly labelled with its designator and value on the PCB silkscreen. Refer to the BOM below for additional details on component types and values.

See the Component Basics guide for help identifying parts.

Software

#

The sequencer runs on open-source Arduino firmware, available on GitHub. You’re free to modify, extend, or completely rebuild the code to suit your own ideas.

polykit/eurorack-sequencer-software

Software for an Arduino based 8-step chainable sequencer

C++

5

0

To upload or modify the firmware, you’ll need the Arduino IDE (or any compatible toolchain) to compile and flash the code to the microcontroller.

Each kit comes with an Arduino Nano pre-flashed with the standard firmware, so you can get started right away — no programming required unless you want to customize it.

Chaining Multiple Units

#

Multiple sequencer modules can be chained together to create longer sequences. To do this, populate the LINK_IN and LINK_OUT 10-pin IDC connectors on each board and connect the modules using the appropriate ribbon cables.

All sequencers in the chain must be powered on simultaneously. This ensures that the auto-detection routine correctly identifies the link mode and assigns each unit its position in the sequence chain.

Once connected, the sequence begins on the first module. When it reaches the final step, control is passed to the next sequencer in the chain. After the last unit completes its steps, a reset signal is triggered, and the sequence starts again from the first device.

The CV and gate outputs are shared across all linked modules, so you can use any output jack to access the combined signal.

If you want all sequencers to share the same clock, patch their clock inputs/outputs together. You can then either:

• Use one sequencer’s internal clock to drive the others, or
• Sync all units to an external clock source.

Extension Port

#

The sequencer features an extension port that exposes all unused pins of the microcontroller. This allows you to create your own add-ons or modify the software for custom functionality.

Some possible extensions include:

• Adding I²C devices (e.g., I/O expanders) to turn the sequencer into a drum sequencer
• Connecting additional potentiometers to analog inputs to modulate sequencer behavior
• Integrating a MIDI clock for external sync

⚠️ Note: Pins A3 and A4 are reserved for chaining multiple units. Avoid using them if you plan to link sequencers together.

First Power-On Check

#

Before powering the module for the first time, carefully inspect all components, solder joints, and IC orientations.

Check for potential short circuits using a multimeter between -12 V / +12 V and ground. For the initial test, it’s best to connect the module to the power supply alone and verify proper operation.

BOM

#

Link to interactive BOM of the component board

Schematics

#