BC9001 or station sign
The BC9001 sign is the sign dedicated to stations in the network.
This sign is placed under the rail and reads the destination of all carts passing on it. When a cart passes over it, if the destination address ofthe cart matches exactly the address on line #4 of the sign, it powers a lever placed on its left or its right, otherwise it unpowers it. The signal given by the lever can be used to change a rail intersection to extract the matching cart and send it to the station.
If the first cart is the head of a train, all subsequent carts passing on BC9001 in the train time frame will follow the head of the train without address evaluation and will reset the train time frame. After expiration of the train time frame following the last cart, BC9001 will operate normally.
Associated with a BC7002 sign, BC9001 can deliver a "busy" signal when a portion of track between it and the BC7002 is not free of cart. A lever placed 2 blocks behind the BC9001 sign is powered if there is at least one cart on the track between the BC7002 and the BC9001, and is unpowered a short while after the last cart hast left the portion of track. The signal can be used to prevent other carts to enter the network while busy. In other words, it can detect a free slot to introduce a limited number of carts waiting to enter the network.
Anyway, if not already unpowered, the lever will always be unpowered 10 seconds after having been powered to avoid lockage.
BC9001 sign must be placed under a rail. At least a lever should be present on the left or on the right of the sign to command an intersection.
Optionnally a BC7002 can be placed upstream on the main track, and gives pulses received on redstone dust on the left or the right block next to the sign. Due to a bug you must use at least a 1-tick repeater to repeat the signal from BC7002. BC9001 will then give a "red light" signal when portion between BC7002 and BC9001 is not free. This "red light" signal can be exploited to create a queue in the station with chained BC7001.
Line #1 : Free
Line #2 : [BC9001]
Line #3 : Station name (will be used to make arrival annoucement)
Line #4 : the address of the station in the form XX.YY.ZZ
The blue line indicates the main track, the red line is the track to the station. Some blocks were removed for better visibility.
There must be redstone dust or a redstone torch on the block with the lever so that the rail changes position when the lever is ON. There is a redstone torch here, but it is not visible behind the block.
Here is the same example with all blocks:
