Introduction

About a year ago, while installing Prusa MK3.5 upgrade kits, we experienced firsthand how intricate the installation process is, requiring careful handling of electronics, display, extruder, and heated bed components. Even for experienced users, it involves multiple steps and attention to detail. Many other users shared similar experiences online. This led us to study the original Prusa design and begin reverse-engineering it. Once we achieved initial progress, we realized it was possible to develop a new interpretation of the system — one that preserves the original performance while making installation simpler and more accessible for a wider range of users.

Motivation

Many 3D printer users appreciate the performance and quality of Prusa machines, but upgrading or replacing key electronics and displays can be a delicate and time-consuming process. ReMIX35 was motivated by the desire to make this process more approachable without compromising functionality. By studying and reverse-engineering the original design, we aimed to create an upgrade kit that simplifies installation, reduces the steps required, and is accessible to a wider range of users.

Audience

ReMIX35 is designed for makers, hobbyists, and technicians who own Prusa MK3S/+ printers that are still in excellent condition — reliable, robust “workhorses” that are often sidelined only due to technological obsolescence. This upgrade kit allows these machines to continue delivering top performance, providing an accessible, community-built, open-source solution for extending their useful life and enhancing the user experience.

Main Components

Einsy-Style Mainboard

• Description: 32-bit mainboard designed for 3D printer electronics.
• Status: Prototype 1 — functional tests ongoing. Development is continuing for Prototype 2, which will include improvements and refinements.
• Files: Preliminary schematics and BOM are available here and schematics. 
• Files correspond to Prototype 1 and are subject to change.

Display PCB + 3.5″ LCM Touch Panel

• Description: PCB controlling a 3.5″ capacitive touch display for the user interface.
• Status: Prototype 1 — assembly tests ongoing. Adjustments are planned for Prototype 2.
• Files: PCB layout and mechanical mount STL files will be shared as they are finalized.

Additional Components (3D-printed parts and screws)

• Description: Parts required for assembly and installation on a 3D printer.
• Status: Still under development; design and configuration may change before the final release.

Note: All files and documentation correspond to Prototype 1, which is preliminary. They are shared to provide transparency, allow early community feedback, and illustrate the current progress. Development is actively ongoing for Prototype 2 to refine and improve the kit.

Features & Specifications

• Processor: Custom 32-bit Einsy electronics powered by STM32
• Motor Drivers: Trinamic TMC2130
• Power Supply: 24 VDC
• Connectivity:
• USB for firmware updates and loading G-code files
• PrusaLink via Ethernet or ESP-01S Wi-Fi module
• Display: 3.5" full-color touchscreen
• Compatibility: Works with Original Prusa MK3S/+ (not MMU3 compatible)
• Installation: Simplified setup using only basic tools (Allen keys and Phillips screwdriver)
• Dimensions:
• Einsy board: 105 × 71 × 21 mm (4.13 × 2.80 × 0.83 in)
• Display board: 125 × 61 × 40 mm (4.92 × 2.40 × 1.57 in)
• LCM panel: 85 × 55 × 4 mm (3.35 × 2.17 × 0.16 in)
• Weight: 300 g (10.5 oz)
• Firmware: Compatible with the official Prusa MK3.5 firmware

Main Features

• Easy Installation: Designed for a simple assembly using just an Allen key and screwdriver.
• Enhanced User Interface: 3.5″ capacitive touch panel for intuitive control.
• Open-Source Hardware: Schematics, BOM, and STL files available for community contributions.
• Flexible Firmware Options: Fully compatible with official Prusa firmware, or custom user-developed firmware.
• Extended Printer Life: Revives MK3S/+ machines...