Block Occupancy Detector For DCC Or AC

With Isolated Output

  This detector uses the "Diode - Voltage Drop" method and has been designed to use a minimum of parts and use as little current as possible when no trains are detected. The circuit takes its operating power from the booster system supply to the rails.

  This circuit has an optoisolated output that can directly control loads of up to five milliamps.

Circuit Design Features

  NOTE: The Current Sensitivity and Release Delay time can be altered if desired. The light emitting diode, D5, can be left out of the circuit if not needed.

Comparator Based DCC or AC Block Occupancy DetectorSchematic

Circuit Board For This Circuit

  This detector was used for the - Grouped DCC Block Occupancy Detectors Installation Test - page located at this site.

  There is no need for the detector to sense current flow in both directions as the longest time that a DCC system can be in the wrong polarity for detection is about 12 milliseconds when zero stretching is at its maximum. The time delay and supply capacitors in the circuit can more than compensate for this gap.

  The detector will work with variable voltage AC systems if a separate 12 Volt DC supply is used to power the detector. If the AC system is a fixed voltage and carrier system the circuit can be connected like the DCC detector but C1 should be increased to 47uF.

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Please Read Before Using These Circuit Ideas

  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.

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18 April, 2016