DCCBD - Signalogic Systems DCC Current Detector

The DCCBD is a Digital Command Control (DCC) track occupancy detector for model railroads.  This detector uses the current-detection method of determining train presence.

Prototypical Track Circuits

Current-detection allows the detection of trains similar to prototypical track circuits.  Track circuits employ an electric current through the rails within a defined region.  When no trains exist, the current slows as intended from one end of the track circuit to the other.  When a train occupies the track-circuit, the metal wheels and axle divert, or shunt, the current from being able to flow across the entire track circuit.  A fail-safe relay or other receiving device declares the presence of a train (occupancy) when the current is not received.  Other failures such as broken wires to the track also result in a disruption of the current and thus allows a fail-safe response when a failure occurs.

Model Railroad Block Detection

In the model railway works, electric current is present on the rails to power our trains.  Current-detectors use the sourced current as an indicator that a train is present.  Rolling stock typically doesn’t have axles that draw power, so some axles are modified to draw some current to detect the train.

Model railroaders refer to current-detection as block detection, however current-detection more closely resembles track circuits, of which signal blocks are made up of.  Track circuits also exist in sections such as within interlockings which are not part of a signal block at all.

DCCBD Features

The DCCBD can successfully detect trains with resistances up to 10 K Ohms.  A continuous current of 5 A is possible through the DCCBD.

The module is powered from a 12 VDC power supply common to all other signal and control circuitry offered by Signalogic Systems.  Duplicate terminals are provided to allow for daisy-chaining the power wiring between detector boards together.

Duplicate terminals are also provided for the DCC buss to allow for daisy-chaining of DCC buss energy to multiple DCCBDs mounted together.

The detector status is provided by a built-in LED that provided instantaneous indication of train detection.  Detection output is provided with 3 seconds of LOS time to ensure occupancies remain prototypically solid, even with dirty wheelsets.

An open-collector output is provided, allowing for interfacing to detection applications such as:

• • • block signaling
    • crossing warning systems
    • staging yard detection.