A feature-rich, NMRA standards compliant DCC decoder in 8K. Targeted at ATtiny84A.
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Don Goodman-Wilson
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A feature-rich, NMRA standards compliant DCC decoder built around the Atmel ATtiny84A.

This project comprises hardware, firmware, and documentation for the Railstars Aegaeon series of NMRA DCC decoders.

The Intent

Let's be honest: Most decoders manufactured in North America kinda suck. We can do better. I want to harness the power of open source development to put together the finest range of decoders available, anywhere. This project has multiple goals:

  • NMRA standard conformance
  • Robustness: decoders should be fault-tolerant, and compatible with widest range of other DCC equipment
  • Size: Modern technology permits really tiny decoders
  • Features: There is no excuse not to have the best feature set possible


The hardware features an Atmel ATtiny84A microcontroller, a high-current H-Bridge with BEMF feedback, and two high-current open-collector outputs for lighting effects.


  • Ultra-compact size (approx. 11mm x 6.7mm)
  • 1A motor outputs
  • Feedback motor control (aka BEMF)
  • 16KHz or 32KHz motor operating modes
  • Two high-current (300mA) function outputs
  • Debugging header for use with DEBUGwire devices like Atmel JTAGICE mk2
  • Trimming of internal RC oscillator is necessary for operation, requires Atmel AVRISP, a copy of stk500.exe, and MS DOS to calibrate. (Welcome to the 21st century!)


The firmware is written in pure C, and can be conditionally compiled for one of three possible configurations (motor only; motor + two functions; H-Bridge-driven function-only). Feature packed, and fully NMRA standards compliant, guaranteed by a stringent set of unit tests (in UnitTests folder, includes Xcode and NetBeans projects so you can run them straight on your Mac or PC).


  • Momentum, 3-step and 28-step speed tables
  • Button-controllable shunting mode
  • Configurable function directionality, brightness, and Rule 17 dimming effects
  • Configurable, button-controllable animations:
    • Strobe
    • Double strobe
    • Rotary beacon
    • Random flicker
    • Left/right ditch lights
    • Mars and Gyra lights
  • Optional soft-start lighting effect
  • Advanced consisting
  • Supports Paged, Direct, Physical, and Operations mode programming
  • Configurable DC operation, or stop-on-DC.


The contents of the firmware folder is licensed under the GPLv3. All other content is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported license

The Future

There are a large number of features I would like to add to this product. I need your help!

  • 2-layer PCB with easy-to-solder components for DIY
  • ATmega328p/AT90CAN128 support for Arduino Uno/Railstars Io:duino
  • Visual Studio project for unit tests
  • Arduino project for easy integration into Arduino projects
  • RailCom support (Railstars has a license to the necessary patents to implement RailCom, need to verify that implementing it as an open source project is kosher)
  • On-the-tracks ops-mode bootloader. Ideally Arduino compatible but that might be a stretch. Would certainly require RailCom to work. But wouldn't that be awesome!?


You can get support for the Aegaeon software at the Railstars Support Forum

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