I'm sure this is a common thread somewhere here on this site, but here goes anyway.
I never used operating signal lights before, just dead ones along the tracks or a few with red leds wired to the block control switches to "sort of" look like the real ones.
It is easy enough to use LEDs pre-mounted or added in to the signal stands and wire them in the circuit of say an Atlas type block switch, so that the Red light would be on, when that block is turned on.
However, in real train operation, blocks are not "turned on" with a switch before a train enters the block, but the train activates the block by its physical presence through a circuit in the tracks.
ALSO, in real train operation, from what I understand, the block in front of the the occupied block, would be lit yellow, (caution) and the next block in front of the yellow one, would be lit green (unoccupied) so all three blocks would have to be lit up, with their correct colors at the same time, to be realistic.
So to get your signals to operate like the real ones, how would you get 3 different blocks, to light up with appropriate different colors repeatedly in different sections around your layout, as the moving train rolled along the tracks?
Keep in mind this is DC and not DCC.
I would check out this system, which claims to work on DC:
http://www.atlasrr.com/pdf/Signals/signalbrochure.pdf
Ed
Website: http://bobfrey.auclair.com
Actually a whole bunch of things happen in a modern signal system. When a train enters a block on single track all the opposing signals drop to red. In territories with speeds above 40 mph or so, there wil be be 3 signals in succession: advance approach (ie flashing yellow), approach (ie solid yellow) and stop/stop and proceed/restricting (ie red, red with a number plate). In addition switch postion will change the signals, so a possible sequence into siding could be advance approach, approach, diverging approach, stop.
There are also differences between an ABS/APB signal system and a CTC signal system. The signal placements are different, the number of signals are different, the signal indications may be different.
Not that you have to model all that, just FYI for how the systems operate.
Dave H. Painted side goes up. My website : wnbranch.com
There are two different kinds of signals, and railroads use both of them.
The first is the Interlocking or HOME signal, and these are indeed controlled by a switch or lever in the tower. It gives a train permission to enter a section of the main line.
Then there are block signals, these protect the rear of a train so that a following train will not run into them. These are automatic signals. On western railroads these can be miles apart, on NYCT these can be as short as 500 feet.
If the tower operator at "Valley" clears a train to proceed northbound, then the operator at "Summit" cannot clear a train to move southbound. "Valley can continue to send northbound trains up the line, when the last train clears "Summit" then "Summit" can send southbound trains to "Valley". Block signals will force the trains to keep a proper following distance.
If you have a small layout, with one or two such block signals, purchased equipment will serve you. If you run the Route of the Broadway LION, with over 200 signals, well the economics are just not there. Actually LION has only 40+ blocks but puts additional signals on each block, just to make things look somewhat better.
Each block requires (on the Route of the Broadway LION) three relays for each block. Here is the "Relay Room" of the LION. Here are two relays for each block, and five wires to the layout for detection, signal, and a remote blocking/starting relay.
Remember, this is for over 40 blocks, you can build a simple device for maybe five blocks on your layout whcih would be rather simple.
Needing more than 200 signals, many of them custom, I simply built my own. Maybe these are not good enough for you, or maybe you are more skillful in construction that a LION with big furry paws.
Interlocking or HOME signals are indeed controlled by the tower. Some signals are controlled by levers as is prototypical, other signals are tied to switches as is normal on most model railroads.
LION cannot affor purchsed signals, him will have to make do with what him builds for scratch, but the LION sure can
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Big Boy Forever,
Signaling is a very complex subject, as your are likely starting to realize from the replies you have gotten so far.
I suggest you find several of the good books that have been written over the years and start reading.
Signaling is no more difficult with DC vs DCC, in fact many modelers through out the history of the hobby have built good working signal systems.
If you have access to back issues of Model Railroader, which you can get online via subscription on this site, you should look up Bruce Chubb and Ed Ravenscroft. Both built great DC signal systems and documented them in the pages of Model Railroader back in the late 60's and early 70's.
Sheldon
Big Boy ForeverKeep in mind this is DC and not DCC.
There is certainly a lot of interest in signal modeling on the forum. It almost warrants another forum category or at least a sticky.
These threads cover some of what you are asking,
http://cs.trains.com/mrr/f/88/t/243185.aspx
http://cs.trains.com/mrr/f/11/t/242936.aspx
Sorry I can't make them directly linked, but right click, copy/paste in another window.
In that first thread you will see my post of some of the signals I have represented on my layout.
Some are interlinked with turnout motors but most are "animated" using the Logic Rail SA type signal animator.
http://www.logicrailtech.com/
Signalling of any kind can get expensive pretty quickly but the signal animator can be had for about $25 and it will work with nearly all types of signals, LED or bulb.
It is triggered by a photocell OR infrared collector/emitter and pretty reliably detects the presence of a train, the sensitivity is adjustable.
When the last car clears, a timer is activated which will tell your signal to go to medium, then finally clear. It is selectable 10 sec. or 30 sec. and doesn't care if you have DCC, DC, battery or live steam propulsion on your rails.
My recent project was a five head, two track with siding bridge and I have different aspects depending on the turnout position for the siding. I even rigged up a Circuitron flasher so I can have a diverging medium aspect. I'll post photos of this soon.
This bridge shows the five heads protecting tracks two and one. Basically, the top heads are for the mains. On the left mast, track two, the center head will show a flashing yellow when the switch beyond is set to reverse (diverging.) There are three pairs of IR LEDs embedded in the ballast between the rails that will drop these signals to red as the train passes over. No need for gaps, resistors on the axels or induction coils on the feeder wire.
These are the three signal animators that are wired to the bridge. The left one is for the siding and it has the flasher (a Circuitron EOT flasher) to give me a diverging medium signal. The other two are for the main line (top) heads. The bottom two heads always show red but they could always be wired to another SA-1 if I wanted to show a more restricting aspect.
Signalling is one area of MR that sorely needs a "plug & play" system. I guess Atlas tried this but AFIK there hasn't been much recent support of their product.
Some modelers seem to push for block detection and a full operating ABS or CTC system but I do not see this as practical on our small empires. In my case, many of the critical signals would be facing a wall or otherwise not visible and not being in the cab of the locomotive, how would I know what signal is showing?
For me, the Signal Animator makes for a nice compromise and I get great pleasure from watching the signal aspects change on their own. One thing I want to do is setup an "eastbound/westbound" switch to override the clear signal if the train is approaching from the opposite direction but this is an option that I'm in no hurry to impliment.
Have Fun, Ed
As I suggested earlier, signaling is a very complex subject.
Ed makes several good suggestions for those not wanting to to go full into this complex aspect of the hobby.
One other approach, is to go with dectection, but to simplify the signaling.
Most all prototype signal systems consist of a combination of "permissive" signals and "absolute" signals. Without going into great detail, think of premissive signals as warnings about conditions ahead, and think of absolute signals like traffic signals on a highway.
For the purposes of most model layouts, premissive signals can simply be eliminated and absolute signals can be used to both guide operators and give great visual scenic effects.
Absolute signals are the signals found before interlockings (a turnout or group of turnouts used to control routes) and are generally the signals controlled by a dispatcher in CTC or by a tower operator.
In this application, these absolute signals are also known as interlocking signals. They will only allow train movements over routes where the turnouts are aligned correctly and the route is clear of other traffic. They are the "traffic lights" of railroading.
By modeling only these signals we can give operators valuable information without actually speaking to them, and they can be implemented with computers, stand alone logic cards, or relays, and we can greatly reduce the complexity of the system - helping to scale it down to our selectively compressed layouts.
Until the last several decades, most signal systems on the prototype where still relay based - in fact, the original relay based position light signals on the B&O, now NS trackage, have just recently been replaced with more modern equipment. The old system was installed in the 1920's.
CTC systems, where a dispatcher controls both routes at interlockings and signals to control train movements, can be done a number of different ways, and can be simplified or streamlined for our model purposes, yet still provide the "feel" of the process on the prototype.
One side note - in Ed's description above, he talks about flashing signals. Understand that these are very railroad and era specific. Flashing signal lights are generally a realtively new idea - last 20-30 years - compared to the whole of the history of railroad signaling.
Anyway, that's just a few thoughts on a very complex subject.