What is it?

The xDuinoRails Thor M is a compact carrier board (shield) designed to turn a Seeed Studio XIAO microcontroller into a fully functional Digital Command Control (DCC) and/orMärklin-Motorola (MM) decoder.

Designed specifically with retrofitting in mind, this board features a standard 21MTC connector interface, making it perfect for upgrading HO scale locomotives, particularly older Märklin models converted to high-efficiency motors.

Why did you make it?

Commercial decoders are "black boxes" that you can't customize. I wanted to create a solution that leverages the incredible power of the RP2040 (dual-core, high speed) to bring modern features—like advanced motor control algorithms and open-source flexibility—to the model railroading community.

What makes it special?

Powerful Brain: Designed for whatever Seeed Studio XIAO board you like (sold separately), e.g. the RP2040 giving you dual-core processing power for complex logic and sound handling.

Standard Interface: Features the NEM 660 / 21MTC connector layout, allowing for a neat installation in locomotives with existing adapter plates.

Robust Motor Drive: Equipped with the BDR6133 H-Bridge driver, featuring low internal resistance (Rdson) for efficient, cool operation.

Note: While the driver is rated higher, the board is designed for a continuous current of 1.0A (limited by the onboard ABS10 bridge rectifier), which is plenty for most HO gauge locomotives.

Smooth Control: Hardware support for Back-EMF (bEMF) sampling via ADC, allowing for precise load regulation (PID control) to keep your train moving at a constant speed up and down hills.

Multi-Protocol Ready: When paired with the xDuinoRails firmware, it supports both DCC and Märklin Motorola (MM) protocols—ideal for 3-rail AC systems as well as the RailCom response channel.

Onboard HT7533 Low Dropout Regulator providing stable 3.3V logic.

Thermal shutdown and undervoltage lockout protection built into the motor driver.