Thinking about the communications issues between the Arduino (DCC++ Master Station), Raspberry pi (semaphore signal control) and the control program on a PC. See Design. I remembered a previous life with the Java programming language and there is a version for the Raspberry pi.

If we connect the Arduino to the pi via USB and the pi to the PC via WiFi this would be ideal. One basic function of the pi would be to manage 6 queues: Send and receive queues for the PC; Send and receive queues for the Arduino; And Instruction from the PC for the pi and return status to the PC.

Documentation for the DCC++ Master Station on the Arduino/Motor Shield mentions GPIO pins being reserved for a WiFi shield. I checked all the WiFi options I could find, and the newer versions use pin 13. Pin 13 is used by DCC++ to control the PWM needed for DCC signal modulation. So, staying with the USB seems the way to go.

Have done a first cut at how to insert instructions for the pi into the stream of instructions to the Arduino that the pi can extract. Basically copies/modified DCC++ approach to sensors/outputs. Thinking about changing the parking lot LED signals to use a bi-color LED.

The order including power supplies and wiring parts arrived today, several days early. 15vdc, 5vdc power supplies and power strip mounted. Arduino Mega with Motor Shield and mods mounted under track. Mounted a DPDT switch underneath to switch track block #14 from "Main" to a "Program" track 

Started drilling holes for IR LEDs and mounting IR sensors - So far working as planned. Exactly where the sensors go being adjusted based on train clearance of turnouts but more based on loco clearance of adjacent tracks and where semaphores can be mounted (loco should stop, on a sensor, before a "stop" aspect).

IR sensors are installed. Still sorting out how I want to wire the Wabbits, Tortoises and turnouts. Setting up PCs and Raspberry Pi 4 for Java development/execution.

Resolved one of two simulator self-induced issues. Insight on another.

Have 5vdc bus installed and 15vdc to the Master Station. Installed the DCC bus and connected to track, the 4 blocks of turnouts including Wabbits. Next step is cables for the Tortoise plugs to the Wabbits and frogs. The wiring side is getting populated/crowded.

Made some progress getting setup to work on Java on a Raspberry Pi. NetBean IDE installed. Getting an error installing embedded JRE on pi memory card.