The Toh Junction display panel above the end of the aisle shows the interlocking is set for an eastward train to enter from the helix up track and leave heading for Browning.

The South Jackson signal, the one we're concerned with, shows red. We're going nowhere until that changes. The signal at the top of the helix "up" track shows green. The red led in the center of the Toh Jct turnouts reports the interlocking is occupied.

The red led on far left helix "down" track shows a descending train has reached to the bottom of the helix and is entering main staging trackage.

All the detection and signaling is accomplished using networked Arduino Pro-mini boards (plus some surrounding logic). All the intelligence is in the Arduino's, an external PC is not used. Long ago, I used to write embedded firmware when I worked at Tandem computers. Homebrewing this stuff was like going home and best of all - I didn't have a boss telling what to do and demanding to know why the project was late!