Model Scenery Tutorials

Comprenshive Tips. Hints And Techniques For Budget Minded Diorama Maker, Model Train Enthusiast And Wargammer

Model Railroad Block Occupancy Detector Types And Operation

A collection and explanation of the various types of block occupancy detectors used to control signal lights using the Model Scenery Signal Driver. Listed detectors include those related to DC and DCC systems.

model scenery modular block signal driverThis is the Signal Driver. Lower in this page are the various types of block occupancy detectors that can be used.

The Signal Driver can be used to control, either normal or approach modes, the various type signals shown below

  • Red, Yellow and Green – 3 Light signals.  Click For Instructions
  • Red, Yellow and Green – 1 Light signals. Click For Instructions
  • Red and Green – 2 Light signals. Click For Instructions
  • Red and Green – 1 Light signals. Click For Instructions
  • PRR Position Light signals. Click For Instructions

Complete information about the signal driver is here. KKKKKK


Block Occupancy Detectors

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.

The Circuits

The 3 Light Signal Driver circuit can be controlled by many types of input devices including most Block Occupancy Detectors designs as well as toggle switches and the outputs of computer system interface cards.

how to connect block occupancy detectorsFor BODs with open collector transistor outputs, the signal circuit and the BOD can use the same power supply and must have a common connection at the minus of the power supply.

Computer system interface cards usually have open collector transistor outputs. The interface card can have its own power supply but will need a common connection at the minus of the power supply of the card and the signals circuit.

BOD’s and interface cards with optoisolator outputs can be used directly and do not need to have a common power supply connection.

A dispatcher can control the signals by using toggle switches to control the signals as shown on the block diagrams. In this case no occupancy detectors would be needed but could be used in conjunction with the switches.

VT-5 Dual DCC Circuit Board

How to use with the VT-5 Dual DCC Circuit Board





Model Scenery Tutorials Block Occupancy Detector

Block Occupancy DetectorUnique Features Of This Block Occupancy Detector:

  • Works with either DC or DCC.
  • Provides positive and grounded output connections so it will provide signal required by your signal driver.
  • Works whether the block track is powered or not.
  • Occupancy status can be displayed on the control panel so one can watch a train’s progress.
  • Block occupancy state can be changed from the control panel. This allows cars to be uncoupled on a siding, the locomotive to leave the block and the block to be manually set by the dispatcher to show it is occupied.
  • Occupancy state is controlled manually by dispatcher or IR sensors.
  • Only two IR sensors, (one a the entrance and the other on the exit of the block) are required regardless of the length of the block.
  • Triggering either sensor gives a block occupied signal. The signal does not change until either of the detectors is triggered or the dispatcher manually changes he state.
  • Works particularly well with out DCC and DC independent block signal controller.  Info is here.

Description of the detector. Click here.

How to use the detector. Click here.


Block Occupancy Detector Helper Circuit

Another detector that will hold a block occupied condition.

This circuit would be used to hold a BLOCK OCCUPIED condition as a train passes out of the block even if the normal detector is not sensing a train.

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 Circuit

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.

Current Sensing Occupancy Detectors That This Circuit Can Help.


Using Diodes At The Occupancy Detector Inputs

The next diagram shows how diodes can be used at the BODinputs of the signals to provide more complex signal schemes. The diodes allow separate input devices to control more than one signal while isolating the BODs from each other during normal operation.

A possible use for diodes at the BOD inputs is at a rail crossing or interlocking where tracks that do not have the right-of-way would have their signals held at RED by the dispatcher until the crossing is clear.

A diode matrix circuit could be used to create complex signal control systems.

block detectionusing diodes


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