chris a posted:… So I am well into building a central relay panel with 24 of these 3PDT relays.
So, for the record, where did you get your 3PDT relays? The jcstudio O-gauge archive website referred to earlier seems to be out-of-service so I think it would be useful to document the relay-method. I found these 3PDT relays on eBay for about $2 per relay "bare" terminals or ~$3 per relay including socket with screw-terminals. *** (see below update with additional info from Chris)
Separately, I can't recall how much documentation there was on the jcstudio site describing the 3PDT relay method, so I sketched out this simple diagram showing how the 3PDT method "works". I put a black "slash" mark on each relay contact that carries "DC-" for the different trigger conditions indicated by the black X on indicating consist axle(s) straddling the outer-rails of the block.
Separately, there is a contemporaneous OGR thread inquiring about converting an MTH PRR signal bridge to this "look ahead" signaling as opposed to the timed-yellow proxy method. In the MTH bridge, the stock circuit board that performs the timed-yellow signaling fits in the signal bridge base. Clearly, the relay method is too bulky if space/size is important. So this would be another application for a compact circuit board as proposed at the beginning of this thread.
*** Update with more attractive pricing and U.S. shipping from subsequent post: