Lineside Signals: B&M Eastern Route

[jbvb]

Presenting at a HUB Division "Railfun Night" yesterday, there was a question about my signals.  The best answer was taking the time to move this old RR-Line thread over:

26-May-2015: 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. Also, not everybody's eyes are up to seeing HO scale point position at a distance.



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):



I've read articles about CMRI-style signals, kept up with Ralph DiBlasi's thread on RR-Line (not saved AFAIK; he was signaling his large HO Lehigh Valley at the time) 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: https://modelersforum.com/index.php?topic=6843.0

[jbvb]

27-May-2015: 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 was experimenting with OC-1s from Olin's Depot (no longer available 10 years later). 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 (no longer available AFAIK). 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.

29-May-2015: Now, components that I hope will make this a lot easier and cheaper than it might have been 20 years ago:



A $3.71 (2015 price) 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.

[jbvb]

An NJI #1295 'Dwarf Signal - SA Type' (alas, no longer available today) 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: (TBD)

29-May-2015: 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).

If Digi-Key had bi-color Red/Green 1.8 mm LEDs (I'm sure they did), I couldn't navigate to them. I found 2-lead red/green at LED-Switch dot com (also gone in 2025). I was also able to find Red/Yellow, which I used in yard entrances.

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. (in 2025, the Hong Kong relays are still working fine).



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.

1-Jun-2015: This interlocking needs a new 3-head searchlight 'home' signal. The location means the ORS 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 had been selling inexpensive signal kits since before 1990. Production got irregular after the founder passed in 2015. I've built several, but 3-head kits like this hadn't been in production since sometime before 2010 - possibly because it's so fiddly getting 6 wires down the 3/32" brass tube mast.

[jbvb]

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 used all the magnification I had, 48:1 if I read the labels on the old 100mm macro lens right.

6-Jun-2016: 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 my homebrew styrene dwarfs installed:

[jbvb]

And here's one Mieke (I was dating her then; she made several contributions to the Eastern Route) took of me under the layout:



Good thing she wasn't around to take pictures when things went to hell.

8-Jun-2015: 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 (electrically, it's grounding) 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.

9-Jun-2015: 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.

10-Jun-2015: This morning, the signal engineer will submit the draft plan for Newburyport to the Superintendent:



After I posted, I noticed I'd cut off the SD-3 labels. From the left, they are SD12e, SD17w, SD16w and SD16e.

Operationally, I need signals in Bexley more than I do Newburyport, but designing this gave me a better understanding of how to protect
non-powered turnouts and use diodes to partition the logic. The diode on this diagram is keeping westbound Block 14's detector and
turnouts from affecting the eastbound signals.

I am cheating a bit, as the 17w stagger block will show double yellow when 16w0 is red, instead of yellow over red. And because block
17 is signaled EB only, 16e shows bottom yellow (call-on) when the double track turnout is normal, regardless of 17's occupancy. Either
could be fixed with another SD-3 driver.

Anyway, this felt good to finish, as the LED power supply was still frustrating me.

[jbvb]

10-Jun-2015:  Feel free to ask questions. I was figuring this out on the fly and anything that isn't clear might not have been thought through. Better to fix it on paper than after it's wired.

Notation (it seems obvious to me, but I devised it):

Block IDs are 2-digit numbers. 09 through 16 figure in the Newburyport plan.

Turnout IDs are block_id T sequence_from_west, so 14T2 (the Hytron spur) is the second turnout in block 14.

Signal IDs are block_id end sequence, so 16e is the home signal at the east end of block 16. 16w0 is the home signal at the west end, and 16w1 is the 'against the current of traffic' fixed red dwarf.

Signal driver IDs add SD to the signal ID, e.g. SD16w0 and SD16e.

Relay IDs add an R to the turnout ID. Only power operated turnouts have relays. Others have a contact on the mechanism to ground appropriate SDs' "Red" inputs.

Detectors ground their output to indicate 'occupied'. Signal drivers operate off grounds at their Red and Yellow inputs. Turnout control is completely independent of the signals.

I'm following prototype practice generally, which is why you'll see electrical block boundaries without signals. It is well known that the B&M didn't do anything like it was made out of money. If a possible signal location wasn't going to earn its keep, the function was implemented on the signal to the rear. This is why there isn't a 14e; 16e does that job. There was little operational reason for EB moves on the WB track at the end of double track, so the dwarf was fixed red. If you needed to pass it, you called the drawbridge operator for permission.

There will be some shortcuts, mostly limitations on displayed aspects and not bothering to display track occupancy on most of the dwarfs. Any current train crew likely to operate here will have been using NORAC rules for at least 25 years, if not their entire career, so my pre-NORAC RR shouldn't trouble their reflexes. If a retired B&M signal maintainer should comment, I'll be happy to listen; it's all modular so $20 for another SD-3 and a few hours designing the changes and implementing them won't be a big burden. But right now I want to prove feasibility and get the basic system up and running.

16-Jun-2015: There will be one change to Newburyport before I start implementing it: I'm being inconsistent about 0-based (signal) and 1-based (turnout) numbering. I haven't decided which to change, but working on the bi-directional double track for Bexley brings it out.

Pete (Orionvp17) asked about 0-based numbering. It's a computer programmer thing - when you're numbering items, is the first one #0 or #1? Most people would say '1', but if you're using the number as an index into an array (a bunch of identical objects stored next to each other in memory), '0' saves a couple of math operations every time you touch an object. That may matter a lot if the objects are heavily used. Here, there's no benefit for counting zero-based vs. one-based, and mixing the schemes reduces consistency and clarity. So I converted signal numbering to 1-based.

21-Jun-2015:  At the previous week's NRHS convention in Rutland, VT I worked on the Bexley signal plan during some idle time:



7T5 and 7T4 are SPDT contacts on the hand-throw mechanisms entering the yard and enginehouse. rDC and yDC are the positive and negative feeds for the bi-color dwarfs I'll use.

This does about 90% of what I want, but I don't have enough contacts on the crossover relay (R6X2) to provide 'call on' (Bottom Yellow) indications on signals 05W, 06W1 and 06W2 at the interlocking's west entrance. I'll sleep on it before embarking on a redraw.

28-Jun-2015: I was feeling happy about progress on dwarf signals ( <TBD> ) so I went to work on designs that use them:



My staging is open and easy to see, so I'm not bothering with detection. I don't really need departure signals either. The east end signals will only indicate Stop or Approach, but the westbound home signal will change between High and Middle Yellow depending on the crossover position. The west end's signals are covered in the single Newburyport drawing since they don't interact with the east end's.

The mechanism slide switches on 01T2 and 02T2 are using all their contacts for the swing blocks & frogs. Adding a couple of SPDT microswitches to their mechanisms shouldn't take an unreasonable amount of under-layout time, though.

And an oops: The dwarf at the west end of the East Lead should be 'D3e', not 'D2e'. I've fixed the plan's track schematic and diagram for 01T2 but I really should build some more dwarves instead of fixing the screenshot above.

9-Jul-2015: I finally got the first interlocking working: Robinson Rd., the east entrance to Bexley yard. This was after burning up the two dwarfs one more time (wiring error, should have documented the actual interlocking board better):



Here's the removable board with the SD-3, relay and DCOD detector, as installed. Next I wanted to start on Newburyport, but I couldn't finish it till I got more Oregon Rail Supply parts.

[Dave Buchholz]

Thank you for responding. Great info here.

[jbvb]

Thanks, Dave. Back to 2015:

19-Nov-2015: Back to work on the signals: East Bexley interlocking proved helpful at my last two op sessions, so it's not just for show. And
over the past 4 months I'd accumulated everything I need to complete the north end of the room:



I'd re-drawn Newburyport to show inter-signal cabling. The longer segments can be done with telco 'quad'. The six wires needed from
Newburyport West across the Merrimack River to Draw will be recycled ethernet cable. The lines from block detectors D14, D16 & D17 come  from the Draw panel because the Olin's Depot detector assumes common rail and I have to put it on the feed side of my  anachronistic block toggles. While I'm building the signals and working out how to make them removable using DIP in-line sockets, I'll add the wire colors to be used for each circuit to the drawing. And fix the 'connection' dots so they show on screen captures and printouts.

30-Dec-2015: I'd been wanting to get back to work on my signals, and Sunday's op session emphasized the benefits I'm hoping for. So I spent the last couple of days implementing the Newburyport diagram above. I wasn't finished, but one bit of engineering has been demonstrated and I've figured out how to address long-haul wiring.

I'd always considered it important that signals react to the position of turnouts. So back when I was building my hand-throw turnouts in
Newburyport, I used DPDT slide switches. One transfer contact for the frog, the other for signals.



Today's wiring got me Stop (three red) at Robinson Rd. when this turnout is reversed, and Caution (high yellow) when a turnout in the
next block is reversed. The center pole is DC ground, the 'closed when reversed' goes to Block 15 Occupied (see below).

If I was doing this 20 years ago, I could have scrounged any quantity of telco 25-pair cable from office renovations. With some 50-foot
scraps, I'd have used different wire colors for every circuit. But what I had today was telco 'quad'.



Now I'm enlightened about how prototype signaling worked. The same positions on the crossarms would often carry different circuits
in advance of a signal vs. in the rear. I'm doing the same with quad under the layout: To the left, Green is Block 15 Occupied, to the
right Green is Block 14 Occupied. Yellow carries Block 17 Occupied through.

I'm noting all this on my printed drawings, to be copied onto the machine-readable files Real Soon Now.

[jbvb]

2-Jan-2016: Over the past few days I had installed my first OC-1 quad DCC-only detector from Olin's Depot (upper left):



It had to go on the feed side of my block toggles, so I replaced the old wiring. Here it's indicating occupancy in Block 17 (EB main through Newburyport depot). The open-collector output is grounding the Oc17 circuit the same way my turnout contacts do. I haven't played with its adjustable occupancy threshold yet.



Looking east from Bexley yard, the 'high yellow' (Approach) aspect isn't ideal, but using bi-color LEDs saved me enough time and money that I plan to get used to it. And I wasn't considering Approach Lighting; At the time I thought that would double the complexity (not true, I didn't know about Rob Paisley's driver boards, but now he's only to be found in the Internet Archive, it seems).



This is about the level of documentation I thought I'd need down the line. I may revise this one more time as I build signals - as shown, 'stagger block' 17w will display 'double yellow' (Approach Slow) when 16w1 shows Stop. The correct B&M rulebook aspect is 'yellow over red' (Approach). RR employees who might notice that won't be operating my layout very often, but it'll probably happen. And I'll know. I can do that if I use a 2nd SD-3 driver and a diode or two.

[jbvb]

3-Jan-2016: Pete (Orionvp17) said this was over his head.  I replied: If you think of the Circuitron SD-3s I'm using as black boxes which turn a bipolar LED red, yellow or green, everything else just grounds the proper Y or R inputs to display the aspects I want. This diagram shows how the 17w 'stagger block' can show Green/Green, Yellow/Red and Red/Red:



The 'High' head defaults to green, shows yellow when block 16 is occupied and red when block 17 is occupied. The 'Bottom' head defaults to green, but shows red when either 16 or 17 is occupied. The two diodes keep blocks 16 and 17 from affecting each other anywhere but at this signal driver.

Next I built the actual 17w signal.

4-Jan-2016: I'd been procrastinating building signals while I wired; today I reminded myself why. The 'stagger block' signal 17w has taken me two or three hours already and is far from complete. Maybe the second will go faster...

Oregon Rail Supply's 'searchlight' parts come closest to what the B&M used, but I need to make some changes and some of the boughten parts are both more fragile and more clunky than those I can make myself. ORS heads & brackets are good, given that I'm settling for T-1 (3mm) LEDs instead of scale-diameter lenses. ORS platforms are better than I can do myself, but I sincerely wish I'd bought more of Free State Systems' etched ladder and platform sets before they folded.



ORS' handrails only work at the top of a ladder, and the B&M had platforms with handrails at each head. Detail Associates .010 x .018 flat brass bar to the rescue. Happily, I didn't melt any of the plastic while soldering the brass:



Here it's ready for ACC on the metal/plastic joints. LEDs, a mounting socket and paint the next day maybe.

[jbvb]

5-Jan-2016: A little more engineering to blog tonight:



I'd seen photos of people using IC sockets as signal connectors, but hadn't bookmarked the pages   I purchased several Mil-Max '8-pin IC socket 0.3" spacing, 0.1" pitch' (DigiKey part ED90048-ND). I won't ever need more than 6 contacts, but the 8-pin parts can't really be cut down. Many different IC socket sizes are available.

I wanted to shim the signal up above the sockets, so I tried out my solvent cements on the plastic body: Weld-On acrylic cement bonded the two blocks of .100 x .125 Evergreen styrene visible between the pins just fine. Once I'd soldered the #30 LED leads into the sockets, I used MEK to bond the styrene signal base to the blocks. Then I soldered two pairs of telco 24 gauge to the appropriate pins on the fixed socket.



Plugged together, the two IC sockets are 3/8" on a side and 1/2" deep. I drilled two 1/8" holes about 1/8" apart, then cut a hole to fit in my 1/2" Homasote roadbed. Here I'm feeding the leads down the holes.



The signal needs a finial and paint and it's lit by the Diode Test function of my VoM, but it's a lot closer to done. It won't take a lot of wiring to hook up the SD-3s, maybe tomorrow.

[jbvb]

6-Jan-2016:  RR-Line members Orionvp17 and BurleyJim had complimented my documentation:  Thank you, Jim and Pete. The documentation is organic to my 'design, THEN build' process. Life is too short (and my back & knees turn 60 in a week) to do this by crawling around under the layout, muttering 'ok, I need another wire from here to over there' and shouting '%$#@&^' when I burn another few LEDs up. I learned from building the first interlocking, so Newburyport's design got revised several times. Implementing Newburyport's signals pointed out several errors in my first design for the bi-directional double track in Bexley, so I'm working on that in parallel.

Bulletin Order #4, January 6, 2016:
Eastward Automatic Signal 17W at MP 36.0, Newburyport, West has been placed in service.






Block 17 occupied, Stop.



Past the end of double track and onto the drawbridge: Caution. The yellow might improve with adjustment.



Into the staging yard and Clear again.  I still haven't put the mileage number on this automatic signal to distinguish it from an interlocking signal. B&M didn't use a flat plate I could letter, instead they attached metal numbers to brackets off the mast.  Hard to execute, and then the mast has a delicate part attached below the lowest platform.  Exactly where I put my fingers when I need to install or remove a signal.

[jbvb]

8-Jan-2016: I was asked about the socket mount: I'm building a couple of 3-light interlocking signals with better photography of the socket work. Because I'm just plugging one socket into another, the pins aren't held strongly - a light impact will knock the signal right over, which I believe is what I want. Somebody who knew more about IC nomenclature might be able to find a 'dummy IC' with pins shaped so they'd be gripped more tightly.

I'm concerned to find that the Oregon Rail Supply website (www.oregonrail.com, printed on packaging) is not resolvable in DNS today. I know the founder passed in Aug. 2015; at the Portland National Train Show, I met his widow at the ORS booth. They had product to sell and she was intent on continuing. There isn't anything else on the market that suits my B&M prototype as well. I thought I had my needs covered, but I just found out the signal heads in part #102 have smaller targets and are molded differently from those in the 'searchlight' range (#125, #127 & #130).

Later that day I got a 3-light interlocking signal ready for LEDs and assembly to the socket:



The upper sockets haven't been modified; the lower left one shows where I remove a couple of molding pins which interfere with the .100 x .125 styrene shim blocks.





This one will be quite close to the audience, and ORS hadn't provided a long enough piece of ladder in their #130 kit. I used Free State Systems (out of business) etched ladder and platforms, soldering all the brass/brass joints. This required care heat-sinking to avoid melting the signal head brackets that had to go between solder joints. And of course I mis-oriented some parts the first time...

[jbvb]

11-Jan-2016: A few more shots as I wired up the socket on the 3-head interlocking signal:



Here I'm starting to insert the LED leads into the IC sockets.



Here, they're all in, ready to solder. I used a 15W iron and Kester .020" rosin core 2% silver solder. And my binocular magnifier. And then I tested all the LEDs again.

Finally, I used solvent cement to bond the ORS base to the two shim blocks. Then I ACC-ed the signal heads in place. Next is wiring the fixed socket. But I started digging around for my bag of heat-shrink tubing (which I was using last week) or my wire-wrap tool (which I haven't used this decade, but did see last year, just can't recall where). No joy on the wire-wrap tool 9 years later. I'd probably have to get a new one off the 'net.

12-Jan-2016: The socket was Mill-Max Manufacturing Corp. '110-44-308-41-001000', 'ED90048-ND' at Digi-Key. The ladder visible here is an out-of-production etched part that Free State Systems used to make, their '8001-1'. Pack of 8 with platforms, nice etching, long enough for any configuration I'd need, but now only on eBay. The 'stagger block' on the previous page uses the punched ladder that ORS includes.

I'm sacrificing flexibility for simplicity in implementation, so this particular signal uses 3 different LEDs to display Medium Clear, Medium Approach, Restricting and Stop: The top head is fixed red, Digi-Key #160-1704-ND. The middle is Oregon Rail Supply's stock bi-color LED. The bottom is a "3 mm red/yellow w/c 2 lead LED" from "led-switch" (since closed). "w/c' meant 'water clear'.

LED Switch also had LEDs similar to ORS', though not with the translucent white 'diffusing' ORS uses. I could probably get a closer match at Digi-Key, but haven't felt the diffusing was a major priority. It probably would help the fake Yellow.

20-Jan-2016: Work continued, but I'm not satisfied with a compromise I made early on. Most dwarf signals and a number of 3-light home interlocking signals will have a "Call On" aspect (yellow, or bottom yellow on a 3-light). I'm driving these from +/- DC voltage using a transfer contact on the associated turnout's relay. An example is R16T1 (relay) driving the bottom head of 16e (home signal) in the Newburyport diagram on the previous page.

This is OK for movements into unsignaled territory. But at Newburyport Draw, signal 16e shows "Call On" even when an EB train is in the  block, and I want to do better. I would like to be able to drive a single bi-color LED based on whether or not an occupancy circuit is floating, or grounded. I could do this with a Circuitron SD-3, but they're $16 and about 2x4 inches. After a couple of fruitless hours searching the web for 'bipolar LED driver' and the like, I checked Paul Mallery's chapter on signals and found no help.

In 2025, I'm still hoping EEs or serious electronics hobbyists suggest a circuit: one input (ground, float) +/-12 VDC power, 2 outputs (one per LED lead) switch polarity based on the input? Must be smaller/simpler/cheaper than an SD-3.

Bulletin Order # 12, January 24 2016:

Eastward 3-light interlocking signal at MP 37.4, Newburyport (End of Double Track) and Westward 3-light interlocking signal at MP 37.7, Merrimack Draw have been placed in service.



The prototype had 500' between Merrimack St. and the end-of-double-track turnout, so their home signal had a conventional foundation. I had to imagine how they'd have addressed putting it atop the retaining wall, too close to the track centerline for a standard footing:

[jbvb]

I set the socket in Wood Putty and built a styrene box to install around it, like they'd poured a pier set into the top of the wall. I'll put some rust spots on it to suggest anchors going deeper into the fill.



Here's the other end, showing the Call On aspect indicating the turnout is lined for the eastward track. I'm living with this for the moment: A friend I've known since MIT had a similar signal project at the North Shore club in Wakefield, and offered to work with me on developing a board using a low- power H-bridge motor control chip, possibly one of the LN293x series. Alas, that never got off the ground..



The westbound half of the interlocking has an SD-3 and a DCOD, set up to detect only the part of block 16 west of signal 16e. This avoids having 16e go red as soon as a WB train pulls out of its staging track, before the train reaches it.



The eastbound half has the relay for turnout 16T1 and the SD-3 for signal 16w1. I've since added a diode across the coil to protect the switch machine contacts.

[edit: picture taken before signal 16w was installed, as indicated by the test LED hanging from the SD-3's output terminals]

Next, I worked on the westbound track, which meant beginning the occupancy detection in the Bexley Enginehouse area.