TYPE-2 — Open-Source Polyphonic Touch Synthesizer (ESP32-S3)

Firmware: v1.6.0 · Hardware: V2 (released) — V3 full-SMT (in development) Author: Alexandre Esnard

The TYPE-2 is an open-source, touch-capacitive polyphonic synthesizer built around the ESP32-S3. Its DSP engine, written from scratch in C++, combines fast polynomial saturation, a dual-rate processing architecture and analog-modeled filters to deliver a rich, expressive sound from a ~€35 instrument.

Featured on XDA Developers (twice) and documented in a full Instructables Featured build guide — see Press & Community.

Core Features

• Hybrid DSP Engine: 7-voice polyphony, fast polynomial saturation and dual-rate architecture.
• Signal Chain: Factorized 24dB/Oct Trapezoidal SVF Filter, Tube Overdrive, analog slop and Studio Digital Delay.
• User Interface: Cylindrical rotary menu, responsive topological grid visualization, preset management.
• Connectivity: Composite USB Device (Native USB MIDI Out + USB PCM Audio Stream) for direct DAW integration.

Hardware Versions

Version	Description	Status
V1	Off-the-shelf modules, hand wiring, copper-tape touch keys	Released
V2	Custom motherboard PCB carrying the modules (ESP32-S3-DevKitC-1, DAC, OLED, MPR121)	Released, Gerbers in hardware/
V3	Fully SMT two-board design, factory-assembled, PCB touch pads	In development, prototype stage

V3 — Fully SMT, factory-assembled design

V3 replaces the module stack with two custom boards designed in KiCad for turnkey PCB assembly:

• Backplate: ESP32-S3-WROOM-1-N16R8, PCM5102A DAC, native USB-C (programming, MIDI, audio) with ESD protection (USBLC6-2SC6), separate low-noise LDO (LP5907) for the analog audio rail, 3.5mm line output.
• Frontplate: 2x MPR121 (QFN) on two independent I2C buses, 24 touch keys etched directly on the PCB, no more copper tape.
• Board-to-board: single 2x4 header, no wiring at all.
• Remaining hand-soldered parts: OLED display, rotary encoder, navigation button, headers.

Goal: production-ready Gerber, BOM and CPL files (with LCSC part numbers, Basic parts prioritized) so that anyone can order an assembled TYPE-2 in a few clicks. These files will be published once the prototype is validated.

V2 Hardware BOM

• ESP32-S3-DevKitC-1 board, 44 pins (ESP32-S3-WROOM-1 N16R8: 16MB Flash, 8MB OPI PSRAM required)
• PCM5102A I2S DAC Module
• SSD1306 128x64 I2C OLED Display
• KY-040 Rotary Encoder
• 1x Tactile Navigation Button
• 2x MPR121 I2C Capacitive Touch Sensors
• TYPE-2 V2 motherboard PCB (or breadboard + copper tape for V1)

V2 ESP32-S3 FORM FACTOR NOTICE: The V2 PCB is routed for the standard ESP32-S3-DevKitC-1 form factor (44 pins, 2x22 headers, 2.54mm pitch). Do not use 38-pin or 30-pin ESP32-S3 boards: their power and GPIO pinouts will not match and will cause short circuits. Always check your board against hardware/wiring_diagram.md and hardware/Type2_v2.kicad_sch before soldering.

Repository Structure

• enclosure/ : 3D models and CAD files for the synthesizer casing.
• firmware/ : Main TYPE2.ino firmware and the type2_audio_bridge.py USB audio streaming script.
• hardware/ : V2 KiCad project, wiring diagram and production-ready Type2_v2_Gerber.zip.
• [hardware/V3/] : V3 KiCad projects (backplate + frontplate) — work in progress.

Setup & Installation

1. IDE Setup: Install the Arduino IDE or PlatformIO with ESP32 board support.
2. Compiler Settings:
   • USB Mode: USB-OTG (TinyUSB) or Hardware CDC and JTAG
   • USB CDC On Boot: Enabled
   • CPU Frequency: 240MHz (WiFi)
   • Flash Mode: QIO 80MHz
   • Flash Size: 16MB (128Mb)
   • Partition Scheme: 16M Flash (3MB APP/9.9MB FATFS)
   • PSRAM: OPI PSRAM
   • Upload Speed: 115200
3. Libraries: Install Adafruit GFX, Adafruit SSD1306 and Adafruit MPR121.
4. Wiring (V1/V2): Follow hardware/wiring_diagram.md for the I2S, I2C and GPIO connections.
5. USB Audio Bridge (optional): Run firmware/type2_audio_bridge.py on your computer to stream audio over USB.

Press & Community

• Instructables: DIY €35 Polyphonic Synthesizer — the TYPE-2
• Reddit: Development log
• XDA Developers: Someone turned their ESP32 into a touch-activated polyphonic synthesizer
• XDA Developers: This open-source ESP32 touch synth just got a massive upgrade

Manufacturing & Acknowledgements

The V2 Gerber files are standard and can be ordered from any PCB manufacturer. Thanks to PCBWay for sponsoring the manufacturing of the TYPE-2 V2 boards.

Roadmap

• 7-voice polyphonic DSP engine
• Tube overdrive, analog slop and delay effects
• Real-time topological grid UI and hierarchical menu
• Firmware optimization and improved menu navigation
• Preset creation menu
• External MIDI communication (USB/Serial)
• Direct USB PCM audio streaming (Python bridge)
• Custom PCB design (V2)
• V3 full-SMT two-board design (schematics done, layout & prototype in progress)
• V3 one-click assembly files (Gerber / BOM / CPL)
• Enclosure for V3
• ESP32 Bluetooth integration
• Battery management for portable use

Links & Contact

• GitHub
• YouTube
• LinkedIn
• Instructables
• Contact / collaborations: alxdreee.esn@gmail.com

Support the Project

TYPE-2 is developed entirely on my own, in my spare time, as a student. If you like the project, you can support it here:

Buy Me a Coffee

License & Copyright

This project is a community initiative for makers and synthesizer enthusiasts.

• Community Use: You are free to study, modify and build upon this project for personal use.
• Commercial Restriction: Commercial resale of this project, its code, or hardware derivatives based directly on this architecture is prohibited.
• Patent Restriction: No patents, trademarks or restrictive IP rights may be filed on this work or its derivatives.