This page is about a block occupancy detector that uses optoisolators to electrically separate the track from the detector output. Three versions of the detector are shown: Basic, Time Delayed and Direction Indicating.
There is nothing special about these circuits and there are other versions of this type of detector on the web and other places. The circuits have simplified outputs that use a minimum number of parts and can be configured to control just about any load device from LED’s to relays.
With the track isolated from the detector output there can be a great deal more flexibility in building control circuitry for a layout as there is no concerns about connecting systems with different power supplies.
The circuits are built around the LM339 Quad Voltage Comparator chip and the H11AA4QT or 4N35 optoisolators.
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