The sub-bus is what you do - see, once you think about it, it becomes pretty obvious. This is why the transformer option is fairly easy to retrofit. Gap one of the rails in the detected zone (both ends, just one rail though), cut the bus wire that all feeders in that zone connect to, and make a jumper that loops through the transformer to connect the bus and this new sub-bus. #18 should be fine.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I priced some camera sets, Yikes. Especially if I need more than 1 monitor.
I'm liking the transformer detector idea better. So I see how a feeder wire gets looped around the sensor and I do undertsnd induced current. To clarify though, all the feeders need to go through the sensor/transformer correct? Do all feeders need to loop around it as well? This could end up making some long feeders.
Or could a "sub-bus" be made and 1 wire of that looped through?
I've got my main DCC bus of 14ga and lots of 22ga feeders installed on the layout so far. If I were to go from the 14ga main bus to set of 18 bus wires (one pair for each staging track) then runs my 22ga feeders to the rails.
I should be able to run a loop of 18ga through the sensor and have the same effect as running a bunch of 22ga feeders through it, right?
Modeling the Cleveland and Pittsburgh during the PennCentral era starting on the Cleveland lakefront and ending in Mingo junction
Noo, the IR sensors will need some circuitry to drive a relay. Again I direct you to Rob Paisley's electronics site, he probably has the very thing. There are also commercial ones. Though I doublt they'd be as cheap as the $5 or per block for the Paisley transformer detectors.
The difference here is that the transformer (and the other current-sensing detectors) show when a loco, lighted car, or car with resistor wheels is within some area of track, an IR detector activated when a train gets to a specific spot and blocks the detector. Beam breakers like the IR detectros are better suited if you want the train to stop when it hits a specific spot, or at least to turn on a light when the train gets to a specicif spot that you don;t want to go past.
Ah clamp on ammeter is that tool I fooled with. Mechanics call them amp clamps.
Yes my staging will be hidden, as in not normally seen when operating. But one side will be open to the aisle, just close to the floor. It's going to be double ended, no stub track though and entered from 2 distant points on the layout (about 36 ft from one end to the other) I'm figuring 5 or 6 tracks plus a through track (access dependent)
So IR detector or light sensor can operate a relay without additional circuitry? I can get lots of relays for free (used but heythey're free) 12 volt and rated from 10 to 30 amps. I'm probably oversimplifying this too...
Just as an fyi, I also have about a dozen trainset powerpacks to use for power supplies if needed
Sort of - they are more like one of those clamp-on ammeters - the kind you just close the jaws areound the wire and it tells you the current flowing in said wire.
Still the same principle as any transformer. Inside those blocks are many many turns of fine wire. You run your feeder wire through the whole, with 1, maybe 2 turns. A small voltage flowing through that wire causes a larger voltage to flow in the coil, which is detected by the additional circuits attached to it.
As for a mirror, the idea woudl be to place the mirror such that the operators can see without bothing to bend down and peer underneath. A workable position may or ma not be found, deending on how your benchwork, fascia, scenery, etc. are set up. I've seen them used for this where the staging is either way up high, or hidden behind a row of scenery. Using it for staging near the floor might be trickier. But it is relatively inexpensive, low tech, nothign to fail, and requires no modification to any wiring or rolling stock to work. It does, however, require operators to pay attention.
For hodden staging though, IR detection can work, especially if the light level is fairly constant. It could even be completely automatic, unless you use mid-train or rear helpers - have the sensor near the very end of the track, but have a gapped section longer than any loco consist, or, if the staging tracks are guaranteed to hold the longest train you run, then just gap each siding. A simple IR dectector would trip a relay to cut power to the track when covered, so it's just a matter of selecting the proepr track and runthe train in, it will stop when it gets to the end, befor it hits the bumper. To get traisn back out, a momentary button or toggle bypasses the realy contact to apply power to the track, until the IR detector is clear. With that sort of a system, even an inattentive operator won;t smash into the bumper.
Greg, no I'm not terribly interested in electronics or building lots of little gizmos. But you are correct that I'm looking for reliable detection in an easy to use form that won't break the bank. Therefore if I can build some small circuits quickly at a savings over off the shelf products I'll learn and do it.
For the record this is HO/DCC and consists will be 1-3 locos (depends on train length)
I scrounged through some stuff that I inherited and found an "amp clamp" meter. This is the type that clips around a wire to read current. So I fiddled a bit with a loco and an isolated section of track, results were interesting. train parked current read 10mA, as the loco ran down the track (about 15 ft) and got closer to the feeder I was reading the reading climbed to almost 250mA. Like a Doppler effect. This may or may not be useful info but it goes to show how much resistance there is in nickle/silver track. I attempted to get a voltage drop reading but the batteries in my DMM were dead.
A mirror is an idea but this staging is under my layout, about 20" off the floor. If one has to get down to see the mirror, there really wouldn't be a need for it.
I looked into these transformer units, and see they are the base of lots of ready made detectors. They look to be what I remember beinig called "step up" transformers, that is they take a low voltage a/c current and multiply it to higher voltage a/c. So a 1mV drop through a feeder gets converted to 350mV right? I know still a small number but do I get the gist?
The EASIEST option is quite low-tech - just hang a mirror. A cheap camera and display would also be extremely easy, if comfort level with model railroad electronics is the deciding factor.
Remember the Twin-T goes way back - having the 75 year MR DVD has allowed me to read the initial articles when it was first presented. At the time, transistors available to the typical person were all germanium, and ones with any sort of current capcity were very expensive. Most systems up til then used relays, which were super cheap as war surplus, but war surplus can't last forever. May sound silly when today you can buy 100 pack of transistors for $5 on ebay, but ina time when $5 was almost a day's wage, blowign a $5 transistor because you goofed blew the hobby budget for a week.
DCC pretty much just eliminates the need for the bias supply and bleed resistor, since the tracks are always powered, unlike a block system where unused blocks have no power in them at all. The other thing it buys you is a great simplification of the circuit - if you put enough capacitance in the output stage so it holds up during the time the waveform is going the opposite direction, you really only need to detect current flowing one way. Worst case this does is delay the detection by the maximum allowed zero stretch - a loco entering the block right at the satrt of the negative half of the signal won;t be detected untilt he positive half, and likewise a loco leaving the block right at the satrt of the negative half won;t be 'forgotten' until at least the positive half starts. Most signal detectors incorporate longer delays than that anyway, to prevent flickering detection with dirty wheels, and in the case of Dr. Chubb's circuits, to "simulated the slow moving and ponderous relays of the prototype". Remember CTC machines sent coded signals to tell a signal or turnout to change state over a SLOOOOOOW serial line - formerly used for telegraph communications. One of the CTC sites has recordings of the relays all clunking away sending out signals, change ONE turnout lever and hit the code button and it clunks away for a significant amoutn of time to transmit the required commands.
rrinkerPart of the reason older circuits liek the Twin-T fell out of favor with the advance of electroncis technology is that they aren't terribly sensitive.
I found a description of the twin-tee detector in the Thorne book and ralize that my description isn't quite right. The diodes across the base-emitter junctions are not necessary if the currents are low (HO or N) and the transistors can pass the expected current. This would mean all the current through the tracks passes through the transistors and detection should be relatively sensitive. While this may not work for one truck with resistors, it may work fine with several in parallel. (With DCC, the track voltage is always on, which should make detection easier than DC).
The diode would provide some protection by limiting the voltage across the transistor and may be needed for O gauge locomotives. So one circuit may not fit all needs.
Another aspect is what the OP hopes to gain: reliable operation quickly in order to build more scenery or operate, or an opportunity to gain some understanding of electronics to better understand all the gadets used on model railroads today.
greg - Philadelphia & Reading / Reading
Part of the reason older circuits liek the Twin-T fell out of favor with the advance of electroncis technology is that they aren't terribly sensitive. A powered loco, no problem, a lighted car, no problem, but they need fairly low resistence wheel sets to detect unpowered equipment left standing. The lower the resistence, the more current each resistor wheelset draws. The transformer type used on our club layout work with as much as 15K across the rals, we put 10K on each car (me, I put a pair of 4.7K, two out of 4 axles, one on each truck, others just do 1 out of 4 axles with a single 10k resistor). Most of ourse are the ones from RR-CirKits.
Rob Paisley has this one: http://home.cogeco.ca/~rpaisley4/DccBODvt5.html
You can buy the pc board and all parts, except for the transformers. The transformers are cheap, overall this would cost less than $5 per block. It doesn;t get much cheaper than that. Maybe if you source the parts yourself and point to point wire them on perfboards, but under $7 for the pc board with all the parts is a pretty good price. The other similar circuit is the Chubb DCC Optimized Detector, works on the same pricinpal but incorporates some delays in the final output so the indication doesn't flicker ack and forth if there are dirty spots on the track. Problem is, even in the MR article on building these, the specs for the transformer were never given, so you'd have to order them direct, at a premium. The RR-CirKits BOD-8 and set of transformers comes in at $6.48 per block, even though it's meant to work with their Tower Control interface device, it can be used as a standalone detection unit and just drive LEDs.
Doesn't get much cheaper than this. Considerign there are some other clowns out there offering block detectors that they calim have all these superior features and are as much as $25/block - and still use diode drops. None of the ones I mentioned here will cause voltage drop to the rails.
ruderunnerTransistors huh? Hadn't really thought about those but that's certainly a possibility. Refresh me on those, IIRC they act kind of like a relay don't they? Meaning using a very low current siginal to control a higher current load.
your idea about placing an LED in series with the track is novel. Presumably you're interested in electronics. But as others have stated, most LEDs can't handle the current through a locomotive. The twin-tee circuit is very similar to your idea except you need a way to know when current is flowing through the diode. And that way is the voltage across the diode (~0.7).
you can read more about transistors on the web. The relay analogy isn't quite right. In general, the current through the base-emitter junction controls a larger current (x50) across the collector-emitter. The diode voltage in the twin-tee circuit is presumably large enough to supply this current into the transistor. A resistor in series with the base is probably needed otherwise you might burn-out the transistor.
an LED-resistor can be in series with the collector of the transistor and when there is sufficient voltage across the diode to "turn-on" the transistor, it should sink current through the LED. The twin-tee may needs an isolated supply (try a 9v battery for starters).
ruderunnerDue to some revision of my layout plans (redesigned and reloacted stagng yard) my staging will no longer be in plain sight. I need some sort of track occupancy detection.
So the question is not about LEDs, diodes and circuits, although these may be a solution. All you want to know is : Is the track occupied.
A staging yard assumes (to me) that you might go around to fiddle with things by hand. But maybe not. But all you want to know is : Is there a train here, or can I put this one here?
1) A video camera will do this for you.
2) A magnet on a metal model board will do this for you.
3) A microswitch with a long drinking straw attached to it can tell you.
4) A reed switch with magnets attached to your cars can tell you something.
LION uses (or at least will try to use) a feather (a drinking straw) attached to micro switch to indicate occupancy on a single track where I will layoup three subway trains for the night. I can cause these switches to open and close circuits as trains arrive, since trains will arrive from the south end of this siding and depart from the north end.
The other way to do this same thing is to just have three switches and to physically turn on or off the poser to each position from the console. The position of the switch ought to tell me what is in there. The TIMETABLE also specifies when and where trains are to be laid up.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
I'd considered using a mechanical switch but kind of discarded that idea due to spac constraints. This is a lower level staging yard. Installing or repairing somthing like that would be difficult. Though that is probably the simplest method.
Transistors huh? Hadn't really thought about those but that's certainly a possibility. Refresh me on those, IIRC they act kind of like a relay don't they? Meaning using a very low current siginal to control a higher current load.
I was thinking of a more analog idea, use a micro switch with lever (or whisker like this: http://www.alpha-crucis.com/en/push-buttons-switchers/3711-micro-switch-w-wire-3-terminal-3700386508202.html) mounted under the layout and attach a 'D' shaped piece of wire (or bend the whisker if already equipped) to the lever that sticks up between the rails so when something rolls over it, it will depress the lever and trigger a light. Sorry for not being able to describe it better, but hopefully you get the idea.
On my old DC layout, I bent a small piece of brass strip over a rail (but not touching it) in a hidden location for loco storage. A wire was soldered to the strip and then to a LED several feet away (hidden, when unlit, in a building window) and the other leg of the LED was connected to the opposite rail. Since the loco was moving slowly into the track (low voltage to the track), when the loco rolled over the strip, it made the strip touch the rail and complete the circut, lighting the LED in the window showing me that the loco was in the clear. It worked great for DC, probably not exactly the circut for DCC but it might give you (or someone else) an idea to start out with.
I loved figuring out cheap ways to do things on that old layout, it really got the brain juices flowing and gave me hours of fun tinkering with scrap/spare parts I've been collecting over the years. As much fun as it was, I agree with others, spending a little money on a 'proper' device would probably work better in the long run and allow more time to work on your layout. Maybe pick up a how-to book on basic electronic projects and surf the internet for circuit diagrams, then hit your local electronics Shack to get all the components you need to build it?
http://delray1967.shutterfly.com/pictures/5
SEMI Free-Mo@groups.io
have you consider Linn Westcott's twin-tee detector circuit (http://homepages.paradise.net.nz/~rdmurg/clinic/detectit.htm).
In general, a higher current diode is in series with the track and a voltage exists across when current flows. The base-emitter junction of a transistor is across the diode and the diode voltage makes the transistor conduct and drive some device (a series resistor limits the transistor base current). The circuit shows a relay, but a modified version could be an LED-resistor.
The twin-tee has two diode-transistor circuits one for each polarity across the tracks. But only one may be needed with DCC if some filtering is added. I doubt this circuit costs more than a couple bucks.
Cheap or thrifty?
My grandfather used to say, "Don't put fertilizer on your lawn until you can afford to put steak on your table".
Rich
Alton Junction
I am a PA Dutchman, we make the Scots look like spendthrifts. Just like the POA Dutchmen who ran the Reading Railroad - our most well known steam locomotives were rebuilt from old ones! And it was not until near the end we even had any purpose built covered hoppers - and even the first ones of those were used. All previous covered hoppers were rebuilt from open hoppers. Even in the diesel era, why buy new locomotives when you can slap an EMD prime mover and hood on an old Baldwin and make a 'new' loco.
I'm so cheap, I buy the 'kit' version of the Tam Valley Singlets to save the $1.50 or so.
ruderunnerRich, I inherited my cheapness though I'm not as bad as my grandma who would wash and reuse sandwich baggies!
I am a Scotsman.
It takes an iron man to play with a toy iron horse.
LOL, gotta love grandmas.
Hmmm, time to go back to the drawing board and the check book. These video monitors are starting to make a bit more sense when thinking that 1 monitor can cover 6 tracks vs 1 detector monitoring 1 track. Price per track starts to equal out. I may have to wait for one of the C628's I want.
Randy, thanks for the explanation, I get it now.
Rich, I inherited my cheapness though I'm not as bad as my grandma who would wash and reuse sandwich baggies!
I was about to chime in with the same suggestion that Mr. Beasley made above.
Being a basement dweller, I set up a Radio Shack camera/monitor by my front door. This thing was great with a 2 way intercom, motion detection that would alert you and relay outputs for whatever function you might want to wire into it, lights, VCR (at the time) bells, etc. I first set this up in 1995 and have been adding to it since.
SO when it came time to set up train detection in my hidden staging yard I looked at all the available options at the time, photocell, IR, current sensing etc. On a double-ended 8 track yard the cost and complexity climbed quickly.
Enter Electronics Surplus or was it All Electronics? They had Panasonic color cameras at $20 a pop. That was my solution, fed through a cheap 4 channel video selector box (later a Pelco multiplexer) and I had a cheap visual occupancy detector. I had an old 13" TV that I put eye bolts in and hung from the ceiling where I could view it easily.
Added bonuses, if anything derails or the train gets broken in two, I see it right away. If you don't have detection in the middle of your yard that can be a problem. I have one camera looking out of a building window just to see the same view my HO peeps have of the passing trains!
I have since upgraded to 16 cameras, a Geovision DVR (not ALL dedicated to the layout) but I can watch hidden curves, junctions and other traffic trouble areas and still keep an eye on the front door for the Pizza or UPS deliveries!
All this stuff was picked up at auction or closeout places for pennies on the dollar.
Maybe this isn't the solution for you but it is another option to consider. I don't have any wireless cameras but with all the motors and electronics going on near the layout there MAY be some interference issues...
Hope this helps, Ed
Well since ruderunner has declared himself a cheapskate, unwilling to spend $20 on a BD20, I'll bet he will consider the camera "relatively expensive".
LOL
richhotrainRelatively expensive, but a highly practical alternative.
Low-end ones are only around $60 brand new. On Craigs List, you can find them for $25. Or, you could pick up separate monitors and cameras, connect them yourself and avoid the extra $20 to attach the word "baby" to the package.
Does your DCC system have an LED to indicate that track power is on? Does it go out when you put a loco on the rails?
When you have an LED across the rails AND a loco in the same block, the LED won;t go out, it';s just an LED (and resistor) in parallel witht he motor - multiple loads in parallel. It's electrically no differnent than 3 different wall outlets in your house, on the same breaker, with a lamp plugged in to two outlets, when you plug the vacuum in the third outlet, the lights don;t go out.
All model railroad detection works on the same principle, sensing the current flowing through the occupied tracks. With no loco and no cars with resistor wheelsets sitting on the track, there is no current flowing, the unoccupied rails are an open circuit. Put something on those rails drawing current, even the slight amount of a resistor wheelset, and it draws a current that can be measured, either as the voltage drop across diodes or transistors, or directly in the case of current transformers.
You can get transformer type detection units for about $5 per block. That's about the best you cna do with an effective system that actually can be used for simple LED activation today and more complex signalling later. Also, since it does not put a voltage drop on the track power, you can install just a few where you want them for now and not worry about the trains changing speed as you move to areas without detection. That simple 8 diode system will work - but it's a 2.8V drop which WILL be a noticable change in train speed from a detected area to a non-detected area, so you'd really need to make everything detected for this to work.
The key is that you need to gap one rail between detection sections. All feeders for that section must be connected via the detector for that block, if you bypass the detector for a few of the feeders, you will have either no detection or erratic detection.
Hmm now we got some ideas going. But a couple questions:
MrB- so bridging the rails wouldn't work even with the loco "jumpering" the tracks? I'm a little confused now, the LED/feeder won't light since the other feeders bypass it, why wouldn't the LED across rails go out if the loco allows a bypass for it's circuit? I realize there will be some resistance from the circuitry in the loco, but if there is enough resistance in the LED combo, wouldn't it go off?
Elmer and Mark: those seem to be workable circuits but are you saying it would have to be a single feeder? Would that be acceptable for a 12 foot "block" of track (trains will be limited to 12 foot lengths)
Rich- I realize there are plenty of off the shelf solutions fo this, I'm just trying to maximize my budget saving where I can.
Have you considered a wireless video baby monitor? Not only can you tell which tracks are occupied, you can also see what trains are on them.
As Randy mentioned, the cheapest, dirtiest, simplest way to do it ....
If you are only running a single engine and a few lighted cars, 1 amp diodes should be sufficient. IF you plan on running more than one engine (2 or 3 in consist), you should really step up to using 3 amp diodes.
This detector, being crude, will cause a 2.8V drop on your track. A train going from a block using this detector to one that does not, will noticeably speed up. A train will noticeably slow down when leaving an undetected block to a detected block. As cheap as this detector is, you could block detect all blocks. The change in speed is noticeable, but you may decide it is tolerable and not worth worrying about. Build a few of these detectors and try it.
If you don't need an indicator for every block, but don't want the speed change, you can leave off the LED's. In this case, the circuit just acts as a voltage equalizer.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
4 diodes in a row one way, 4 more in a row the opposite way, will work. With a lot of voltage drop to the rails, about 2.8 volts.
Not sure how Digitrax does it, but they do a 2 diode drop per block - the BDL168 has 5x bridge rectifiers for detecting 16 sections. The RD2 remote sensore is basically just a bridge rectifier you wire back in to the BDL168
If you had on-board power instead of track power, you could do something similar to the real thing - power held a relay up until the metal wheels and axles of the train shorted across the rails, causing the relay to drop out.
The type of systems using a transformer are generally superior to the diode systems, since there is no voltage drop and you won;t have to worry about speeds varying between detected areas and areas without detection.