After a lot of research, I chose RR-Circuits as the vendor I would use for Block occupancy detection for my model railroad. I determined these products to be one of the most cost effective as well as the most compatible with my vision for control of the model railroad. I am using a BOD-8 detector with the Towerman 16 port I/O board and a Simple Serial Port gateway I had used for experimentation. I also purchased four more BOD8 boards and a TowerController Mark II 64 port I/O controller which interfaces directly to Loconet. There are a total of 33 detected blocks on the WVR.
Shown below is a depiction of the system used for block detection and turnout control on the WVR. One of the advantages of this method for block detection is the use of CAT5 connection to the remotely located detection coils. The I/O controllers also allow for button inputs and 5V outputs. The JMRI computer uses Loconet messaging to display the location of occupied track. This also allows for signal control through JMRI. Wiring is also significantly reduced. The only layout wiring required is the DCC bus, a 5V bus for power, and the CAT5 wiring to the detection coils. All the other wiring is local to the devices used.
Below is one of the busier panels on the layout which is used for block detection. The four boards labeled BD1-BD4 are the BOD8 block detectors. Each board is connected to up to eight detection coils via the cat5 network cables. A 10-conductor flat cable connects them to the TowerController Mark II which requires 12V power and a connection to Loconet. The board on the lower right is a breakout board used to receive inputs to from facia mounted pushbuttons controlling turnouts and automatic uncouplers. The Tower Controller outputs the DCC messages on the Loconet buss and in turn the Digitrax command station receives those messages and transmits them on the DCC buss to control the various accessory decoders located throughout the layout. The inputs and outputs on the TowerController are easily set up using JMRI Decoder Pro, similar to programming a decoder.
I mounted the detection coils to a piece of plywood with E-6000 glue, then drilled a hole in the center for the wires to pass through. The Cat5 cable pairs were then soldered to the coil leads. These assemblies were mounted near where the 18-gauge sub buss wires were connected to the DCC buss terminal strips. The single wire passing through the coil generates a signal when even a slight amount of current flows through the wire.
Current from locomotives will obviously trigger the detector, but I also add resistors to two axles on each new car I add to the roster. These resistors are 10K surface mount devices glued in place as seen below. Looking closely, you can see that I have bridged the plastic insulator on the axle with the resistor.
I clean the area where the resistor will be glued and scuff the area with a sanding stick to make sure there is good contact. A small dab of gel superglue is used where each end of the resistor will touch, being careful not to cover the contact surface of the resistor. I then use a micro brush and apply conductive paint to bridge the gap between the resistor and the metal of the wheel set. Once the conductive paint dries, I check the axle with an Ohm meter to make sure the connection is good. Here are a couple of wheelsets ready for use.
