Description
The MIDI8d+ (Plus) is a 4HP wide, simple and versatile Eurorack module that outputs 4 digital gates and 4 PWM analog CV signals, from a single MIDI TRS input connection.
It is an upgrade of the MIDI8d: four of the eight digital outputs have been replaced by filtered and buffered PWM analog outputs, making it possible to generate Control Voltages (CV) directly from MIDI, without any additional hardware.
Four analog outputs
The four analog outputs are generated by PWM (Pulse Width Modulation) and passed through a low-pass filter to remove switching noise. They are also buffered, so the CV value remains stable regardless of the load.
PWM CV is an affordable and convenient solution, but it is not ideal for applications that require very precise tuning (e.g. VCO pitch tracking). It works well for everything else:
- VCF cutoff frequency
- VCA level control
- Delay time / feedback
- FM modulation depth
- Audio-rate modulation signals
Output #5 has 16-bit resolution; outputs #6, #7 and #8 have 8-bit resolution. The analog outputs are identified on the front panel by inverted (light-on-dark) numbers.
Note: due to the filtering network, the four analog outputs have a slightly slower rise time than the four pure digital outputs. If you only need fast-rising gate signals, the MIDI8d is the right choice.
Firmware: open and reprogrammable
The core of the MIDI8d+ is a classic Arduino Nano (ATmega328p), programmable with the free Arduino IDE. Different firmware sketches can be uploaded to adapt or completely change the module’s behaviour.
Firmwares are cross-compatible between MIDI8d and MIDI8d+. All sketches written for the MIDI8d can be used on the MIDI8d+ (note that output pin ordering differs: see source code for hardware mapping).
Typical uses:
- 8 drum trigger outputs, reacting to MIDI Channel 10 (notes 36 to 43)
- MIDI Clock with various time divisions and Start/Stop Gate outputs
- Monophonic MIDI-to-CV converter (pitch + velocity)
- MIDI channel activity monitor
- … and many more: write your own!
Open source firmware repository: https://github.com/dhaillant/midi8d/
Hardware
The module consists of two PCBs:
- the Front PCB, supporting all jack connectors and LEDs
- the Rear PCB, supporting the Arduino Nano and the Eurorack power input
The +5V rail is generated on-board by the Arduino Nano: no separate +5V bus required.
The MIDI input jack is a stereo TRS Type A connector (Tip = Sink, Ring = Source).
Many components are in Surface Mount Technology (SMT). Check out the pre-assembled SMD option: with this option, the only remaining components to solder are classic Through Hole parts, making the build accessible to beginners.
Documentation and resources
- Full documentation & schematics: https://www.davidhaillant.com/midi-8dp/
- Source code: https://github.com/dhaillant/midi8d/
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