As they say a little knowledge is a dnagerous thing. I'm no electronics genius but I do understand some basics of wiring.
Due 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.
Would it work if I wired an LED into a track feeder for a staging track? The thinking goes like this: the rails, when properly gapped, have no power passing through the feeders when the track is unoccupied. This would keep the LED off. Now if a loco, lighted car or somethigs with resistor wheelsets bridges the gap between the rails, it completes the circuit causing power to flow and hopefully lighting the LED. This is for DCC since the bus has power all the time.
Or, would the electricity bypass the LED and just pass through the other feeders?
Modeling the Cleveland and Pittsburgh during the PennCentral era starting on the Cleveland lakefront and ending in Mingo junction
My initial guess would be that the current draw of the train would be much more than a LED in series would be able to handle.
Brad
EMD - Every Model Different
ALCO - Always Leaking Coolant and Oil
CSX - Coal Spilling eXperts
You would really need one of these or an equivalent: http://www.ncedcc.com/component/virtuemart/?page=shop.product_details&flypage=flypage.tpl&product_id=63&category_id=16 (NCE BD-20)
Another way would be to utilize some sort of infrared circuit.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
That NCE BD20 that maxman suggested is a simple, reliable device and not all that expensive. I use them to trigger my crossing signals wherever the track intersects with a road. You gap the rails and loop a wire through the ring on the BD20 and you are good to go for occupancy detection.
Rich
Alton Junction
Ahh I see I wasn't terribly clear abut the feeders, the LED feeder would be an add on to the primary feeders, not the only source of power for the loco. Though it'sa good point about the voltage passing through it.
LED are diodes, they just light up. From my understanding of diodes, no power passes through in one direction (no light) but does in the other (lights up) A check valve for current flow if you will. Therefore the A/C like DCC siginal "should" be acceptable with current flow through it approx. 50% of the time.
I'm also a cheapskate, a pack of LED's and some wire should cost less than 1 premade detector
Think about it for a second, or better yet, draw it out. You have a red buss wire and a black buss wire, both of which are attached to their respective red and black rails.
You are wanting to attach another feeded from the red buss wire, through an LED to the red rail. At no point does that red rail ever become the black rail in order to light the LED.
Mark.
True that the red rail doesn't change to black. And if no loco is present there is no current flow between the red and the black. But when a loco "completes the circuit" between red and black rails, current begins to flow through the feeders (LED included hopefully)
All the red feeders are parallel circuits controlled by one switch (the loco being present or not) This is why DCC can work with just 2 wires connected to track, but works better with multiple feeders, each feeder carries some of the load.
As an alternative, what if the LEd/resistor bridged the rails? The LED would be lit if no train was present, would it go out if a train was present? This I believe would be dependant on the resistance of a decoder/lighted car/wheelset versus the resistor needed for the LED.
I'm not particular on wether the on or off aspect means occupied, as long as the other aspect means unoccupied
No, the current will only flow through the feeders without the LED. They have effectively zero resistance. You will need at least a few hundred ohms in series with the resistor to keep the LED from becoming a DED (Darkness Emitting Diode.) With a zero-resistance path in parallel with the LED and resistor, there will be no current going through that path at all.
Another way of looking at it is to observe that the feeder is effectively a jumper across the LED-and-resistor combination, so the voltage across them will be effectively zero, so that no current will flow.
It takes an iron man to play with a toy iron horse.
That was kind of what I was afraid of, figuring the powwer would bypass through the other feeders. Maybe the others were saying the same thing, you just put it more succinctly.
That said, what about option 2, bridging the rails with the LED? Or asked differently what kind of resistance would a decodr provide since the resistor for the LED can be changed within a range that may still work.
ruderunnerThat said, what about option 2, bridging the rails with the LED?
No, sorry. That would just keep the LED on all the time.
Have you considered using an infrared LED and an infrared detector? These are relatively cheap, although you'll need some resistors and a power supply to support them. Use the detector to turn on a panel LED. Infrared will be less sensitive to room light than visible.
OK, here is another idea.
Back in the heyday of DC, there was a circuit for constant lighting for locomotives. This may work for your detection scheme, but I am not sure although it seems logical.
Three diodes were connected in series and a low current 1.5v light bulb and a single diode in series with the bulb was connected in parallel with the two diodes. This small circuit was put in series with the motor of the loco. When the train would run, the current would pass through the diodes. The three diodes dropped 1.8v and could be read with a meter, this small voltage would light the bulb through the other diode (which would drop .6v bringing the voltage to the bulb down to 1.2v). Now, this would only allow the loco to run in one direction, so three other series diodes were added in parallel with the first three, but backwards. The result was that the light would only light in one direction, and the diode in series with the bulb prevented the bulb from lighting in the reverse direction.
Since diodes will pass a DCC signal (Digitrax uses them in it's BDL-168) this cheap circuit may work for your detection. You also may be able to put an LED in place of the 1.5v light bulb.
The circuit would be put in the main feeder to the track and all other feeders would have to be connected to it so there is only one path for the current to the track.
---|<--|<--|<--- D1, D2, D3
---|<--O------- D4, Bulb
At this time, I am not sure about the polarity of D4.
--->|-->|-->|--- D5, D6, D7
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
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.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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.
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.
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.
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.
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.
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
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
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!
LOL, gotta love grandmas.
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.
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.
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".
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.
greg - Philadelphia & Reading / Reading
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
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.
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