Block Occupancy Detector Helper Circuit
The Helper circuit uses phototransistor type light activated detectors to sense that a train is still in the block, even though the engine has left that block.
The only reason to use this circuit is if there are no conducting wheel sets at the tail end of the train that would keep the normal occupancy detector activated until the train has completely exited from the block.
Simply stated the Helper circuit’s output is in parallel with that of the normal detector. When the Helper circuit is activated by a train covering one of the phototransistors at either end of the block, the Helper’s output holds the block as occupied even though there is no current flowing through the sensing circuit of the normal detector and has therefore turned OFF.
Block Occupancy Detector Helper Schematic
Block Occupancy Detector Helper Notes
- The Helper has a short delay built into its release.
- A more detailed description of the basic functioning of this circuit can be found on the Voltage Comparator information page at this site. See the “Comparator Timer Delay” section of the page.