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APB/CTC unified intermediate signal

The unified APB/CTC intermediate signal is a replacement for both the APB intermediate and CTC hold signal modules, incorporating their functionality in one software version. By writing a configuration variable in EEPROM, the desired functioning can be easily switched, without any need to touch the firmware.

Introduction

This module was designed for controlling two APB intermediate signals, that stand at the same location and govern opposing movements. They can be of any head number, as six individually configurable outputs for each signal are provided. There are inputs for two current-sensing block detectors, and one infrared detector at the block boundary for detecting non-current drawing vehicles. These track circuits are circuit A for both signals, and circuit B for those adjacent (refer to the APB implementation document).

This version features approach-lighting, but that can be turned off and on with an uppercase 'X' packet, with the byte number 6 (first data byte) containing 0xFF (signals are ON) and 0x00 (signals are approach-lit), respectively. This is also useful for system checks and debugging. As implemented, both signals have a yellow-only lower head, but this can of course be changed.

Photo of an APB/CTC unified intermediate signal installed on a short americaN module

Please refer to the document CTC Command structure, section 3.2 for information on how the display packets look like. You can find it here. The APB node of course only sends information related to track circuits, which are "Occupancy" and "Clearance" (OCC0-n).

As for PCBs, fellow model railroader Oliver Hampel of Munich designed industrially-made boards we both use on our modules. If you are interested, contact him at olha (at) arcor.de. These APB boards are very useful, as they incorporate everything necessary for the node, from block detectors to MRBus sockets (see the schematic below). Additionaly, I think there is a wide range where you can use them: CTC control point node, or even an MRBus-PC interface, where a suited controller is mounted on top on the board, are just two examples I built.

Photo of an APB intermediate PCB installed on the above americaN module

Documentation and Source Code

Memory Map and Tools

Schematics

Source code