The purpose of this circuit is to allow signals circuits such as the "Circuitron DT-2 Grade Crossing Detector", that use track polarity to determine the direction the train is traveling, to be used with DCC systems.
The circuit uses four phototsensors placed in the same positions along the track as those of the Grade Crossing Detector circuit to determine and hold the detection of the train until it has passed out of the protected section of track.
The direction detector holds its output for about 10 seconds after all of its photosensors are uncovered.
The direction detector uses its own phototsensors but could use the sensors of an existing signal circuit if the power supply and common conections are compatable.
Two versions of the circuit are shown on the schematic. The upper circuit is a full version and has LEDs to indicate when a phototsensor is covered by the train and which output is active. The lower circuit has only the components required for the circuit to function properly.
The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.
If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.
Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.
13 January, 2019