The MRX1 crossing system controller senses train movement near a model railroad grade crossing, and uses that information to operate crossing signals and crossing gates.
This system works well with position sensors such as the MRD1 infrared train detector, or with block occupancy detectors.
Position sensors detect the presence of a train at a particular spot on the model railroad layout. Installation of the MRD1 infrared train detectors is explained on the installation how-to page.
Block detectors sense the presence of a train in a track block. A block is a length of track that has one rail electrically isolated from the rest of the layout. Power to that rail is routed through a block occupancy detector. When the block detector senses current flowing into the track block, it switches its output to indicate that a train is present.
This wiring diagram shows how to connect the MRX1 crossing system controller to Atlas 233 Block Detector Boards (BDB). In this example, the track is divided into three blocks. The West Block is to the left of the road crossing, the East Block is to the right of the road, and the road crossing itself is the Island Block. Each block has its own block detector.
The three diodes are part no. 1N4001, 1N4935, Radio Shack 276-1620 or similar. The block detectors connect their output to 'Com' (negative side of the power supply) when a train is sensed. When a block is empty, the block detector goes to a positive voltage that is higher than the +5volts used on the controller board.
The diodes are required. They prevent current from being pushed backwards into the controller.
