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Lineside Signals for the B-and-M Eastern Route

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  • Lineside Signals for the B-and-M Eastern Route

    My layout doesn't have much hidden track, and only one out of sight turnout. When I'm running by myself I can either see the points or see a control lever that shows the position of the one I can't see. But my guest operators sometimes lack that local knowledge, or maybe the vision.

    I've been thinking about signals ever since I got the basic control system working. This shows my guess of how B&M practice would have been applied to my Bexley Tower interlocking (the lower right corner of the track plan image):


  • #2
    I've read articles about CMRI-style signals, kept up with LVRalph's thread (
    and operated with them on home layouts and the Hub Division's modules. But I didn't want them at home:

    1. For mainstream installations, if the computer isn't running, power turnouts can't be thrown.

    2. At startup, those I've seen take time and effort to get the computer's view of turnout state to match the layout's.

    3. Local control can be done, but each sub-panel takes a computer and extra implementation work beyond that required for a single CTC console.

    4. Each computer is a point of failure, and requires at least a little system admin work from time to time.

    What I want is lineside control, where logic at a given interlocking does most of the work. In my area/era, that logic got its orders from
    nearby signal towers and occasionally manual pushbuttons on the relay cases.

    Some commercial firms offer local logic boards which can be configured to reflect a particular track layout. But the more complex their
    options are, the more they look like programming a modern hotel room clock. Or sending text messages from a flip phone. Not the right
    UI for the complexity of the task. And no source code, so I'd have to work around any idiosyncrasies. And some of them didn't have
    components to handle the multiple-head searchlight signals my prototype used.

    What I settled on is a mix of relays, commercial detection components and commercial signal head drivers. With cheap automotive
    relays, I ought to be able to keep the cost below $50/block, less in single-direction double track. If the cheap relays don't
    stand up to my low-current application, I write off their $4/turnout cost and spend $25 for a better grade.

    I maintain and use a layout-wide cab control system, with one block toggle position connected to the DCC buss. A plus for my lineside
    signaling scheme is that I should be able to indicate turnout position regardless of whether the block that it's in is being powered by
    DCC or DC. And if I find a power-agnostic detector that doesn't require common rail, the rest of the logic should work with it.

    My B&M Eastern Route layout thread is here:

    My next post, later this week, should be the plans for the first interlocking I'll build.
    Last edited by jbvb; 12-17-2021, 10:56 AM. Reason: Fix link to LV Ralph's thread, add link to Eastern Route thread.


    • #3
      Looking forward to this.


      in Michigan


      • #4
        The first interlocking I'm going to do is the east throat of Bexley yard. It's a single switch entering a main track whose normal

        direction is eastward (left to right in the XTrkCAD diagram).

        SDxx will be Circuitron SD-3 bipolar LED drivers. For the Dx detectors, I'm experimenting with OC-1s from Olin's Depot

        ( This interlocking isn't an ideal application, as I can only reasonably

        feed two blocks from this point, leaving the other two detector units idle. Mast signals will be searchlights from Oregon Railway

        Supply. Dwarfs are probably going to be kit-built or scratched.

        To do the full logic, I'd have needed two more SD-3 cards. I've simplified it so when the turnout is thrown for the yard, the eastward main's

        home signal will go Red and the two dwarfs will go Yellow (Call On). The bottom line is about $45, not including the switch machine.


        • #5
          Now, components that I hope will make this a lot easier and cheaper than it might have been 20 years ago:

          A $3.71 automotive 4PDT relay with LED indicating the coil is powered. I bought a 10-pack from an Amazon vendor in Hong Kong.
          All the coils read between 117 and 119 Ohms, so they'll draw 0.1A at 12 VDC. When I went to ring the contacts out, I found one side
          of one pole bad on the first (red X). I will report how the rest turn out.

          Depending on how far I go with this, I might need to know point position on between 3 and 5 old Kemtron-style twin coil switch machines
          that are already installed. I really didn't want to solder multiple wires to the contact fingers. Spending an afternoon researching
          slide-on connectors turned out to be a lot easier than removing and re-installing the switch machines:
          These FDD2 units for 0.187 blades cost $12 for 200. I'm using 0.25" Kapton tape to insulate them. If I need both a machine's contact sets,
          I'll probably cut off the crimp portion and solder wires to the slide body.

          An NJI #1295 'Dwarf Signal - SA Type' dunked in acetone and re-kitted. With a bi-color LED that fits, I might need a dozen on the layout, and
          a couple of their 2-head cousins.

          Edit Long After: I wasn't able to file a 1.8mm LED package down enough to fit into NJI single dwarf head castings. The 2-light castings are enough larger that I could upgrade them to bi-color. I scratchbuilt 9 single SA dwarfs as described here:
          Last edited by jbvb; 12-17-2021, 11:04 AM. Reason: Update w/link to Prototypic Dwarf Signals thread.


          • #6
            I'm enjoying this thread, please keep it coming! One thing I'd like to see is a logic diagram showing what you're trying to achieve with the set of signals.

            Modeling 1890s (because the voices in my head told me to)


            • #7
              Explanation I should have included with the purple part of my schematic above:

              The OC-1's occupancy detectors are NPN open collectors that I'll set up to ground their output when occupied. They can

              sink up to 25 mA. Circuitron says the SD-3 draws "a tenth of a milliamp" on its Red and Yellow inputs.

              So Detector 13 (block 13 in diagram above) will pull down SD13wR (Signal Driver West 13 Red input) and SD11wY (11 West Yellow)

              when the block is occupied. This is the standard way to wire Circuitron SD-3 drivers.

              The 'from switch machine' lead will have +12 when the turnout is reversed, so the relay will pick up. This will ground

              SD13wR, changing the eastward home signal's top head to Stop (red). The home signal's two other heads are fixed red and

              their wiring isn't shown. Other relay contacts will change the two dwarfs from Red to Yellow (not strictly prototypic).


              • #8
                If Digi-Key has bi-color 1.8 mm LEDs, I can't navigate to them. I found 2-lead red/green here:

                If I find red/yellow, I can use them too. So now I'll buy the rest of the NJI dwarfs I need.


                • #9
                  I tested the rest of the relays: two each a normally-closed contact which didn't conduct. But taking them apart and pulling a strip of

                  paper through the offending contacts fixed them.

                  Since East Bexley only needs one 'make' and one 'transfer', I spent a while seeing if I could do it with the switch machine's DPDT auxiliary

                  contacts (there's another 'transfer' but I'm using it to power the frog). As my rusty basement refugee Kemtron demonstrates,

                  even simple modifications don't give this kind of slide-on connector access to all the machine's contacts. Rather than strain

                  things to avoid the relay, I'll do it as I drew above, with one 'make' on the switch machine to power the relay.

                  I can't do the dwarfs till the LEDs arrive, but I can build the home signal, wire the relay, detector and signal driver and maybe see

                  'first light' over the weekend.


                  • #10
                    This interlocking needs a new 3-head searchlight 'home' signal. The location means the plastic platforms & railings would be both protected

                    and not looming in the foreground of photos, so I didn't use my out-of-production Free State Systems etched parts.

                    Oregon Rail Supply has been selling inexpensive signal kits since before 1990. I've built several, but 3-head kits like this haven't been

                    in production since sometime before 2010 - possibly because it's so fiddly getting 6 wires down the 3/32" brass tube mast.

                    After applying some profanity followed by Floquil Bright Silver, I set it aside and unpacked the 1.8mm LEDs that came in today's mail:

                    I gave up on trying to bend the leads to fit the stem of the signal casting as the ?Chinese? had done with the original - they'd probably

                    started with axial leads. Instead I soldered 30 ga. Kynar to the cut-off stubs. This photo uses all the magnification I've got, 48:1 if I

                    read the labels on the old 100mm macro lens right.

                    [edit] Sorry about the sideways photos; My computer showed them normal. I won't use that resizing tool again.


                    • #11
                      Cool mast, James!



                      in Michigan


                      • #12
                        Thursday the signal project made a good deal of progress: first light at the Robinson Rd. (East Bexley) home signal. But I didn't take a

                        picture and Friday made mistakes which undid most of it (6 LEDs burned up by two different mistakes). Here's one of the dwarfs installed:

                        And here's one Mieke took of me under the layout.

                        She wasn't around to take pictures when things went to hell. More when I actually manage to advance things (parts to do so may not arrive till Tuesday).


                        • #13
                          Now, there's a handsome lad below deck!

                          James, great following along as you signal the line.

                          The layout look great as always! [:-apple]
                          Mike Hamer

                          Ottawa, Ontario, Canada





                          • #14
                            The final (I hope) version of Robinson Rd. Interlocking passed an out-of-place test this evening:

                            +/-12 VDC and ground enter at the top left. The Circuitron SD-3 signal driver is to the left. The three terminals above it will control

                            the two dwarf signals from the 4PDT relay at center. A Chubb-design DC Optimized Detector I bought from BurleyJim is at right. The two

                            terminals with jumper at the top center go to the track. The DCOD is pulling down the Red pin of the SD-3 and it's indicating Stop on the

                            Oregon Rail Supply dwarf I'm testing with.

                            The wires from the switch machine contact to operate the relay aren't present; I tested them Friday. I also need to install a diode across

                            the relay's coil to protect the switch machine contacts. The wires to the active head of the home signal and the Yellow input to the SD-3

                            will enter the assembly via slide-on connectors.

                            Lessons learned so far:

                            1. No matter how tiresome it is to get the 30 GA wire from the signal properly gripped in a terminal block, it's worse to fix a signal in

                            place because you can't pull heat-shrink splices back through the baseboard.

                            2. The DCOD is more economical for single installations, but also works better with the 'Remote' blocks on my layout because they don't

                            care whether the Master block is set to DC or DCC. I'll eventually use 5 more DCODs for Remote blocks, with Olin's OC-1s for the main panels.

                            3. If I'd built/debugged the dedicated 2 VDC LED power supply first, I'd have saved myself 6 LEDs and a signal handrail and the whole

                            interlocking might be in service now.

                            4. Test everything at every step, but don't do initial tests of control electronics with with layout-quality signals.

                            5. Stranded 30 GA DCC decoder wire is lousy for soldering to tiny LEDs.


                            • #15
                              The eastward home signal is now indicating both turnout position and track occupancy well enough that operators should be pleased.

                              It won't show Yellow until I install signals in Newburyport.

                              I started designing the end of double track/drawbridge interlocking at Newburyport, so I haven't finished the 2 VDC power supply.

                              The fixed LEDs in the home signal are waiting on that. The two dwarfs that only indicate turnout position need that, plus

                              me finding a reliable set of steps that will make a 1.8 mm LED fit into them while still displaying both Red and Green.