Train on Track detectors.

Having reached the stage of wishing to indicate TOT to prevent any
more senior moment accidents I decided to make up one of the Roger
Amos offerings. On testing and thinking about it ( as opposed to
just making it), it became obvious that these little devices will
function with or without controller power being present and simply
require to be attached to each rail to provide the circuit through the
on-track motor. It does help that when one of our computers died I
was able to re-use the Power Unit to provide wedges of 12 & 5 volt DC.
Have any of the fraternity used these Twin Tee units in such a manner?
If so, have any drawbacks been revealed ?
Regards
Reply to
Sailor
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Yes. Cost. (which can be reduced with modern circuitry)
Detectors come in two broad categories: - passing a point. - stock in block detection.
They can also be divided into: - general detection. (all rolling stock detected) - specific trigger detection. (eg magnet or trip on rolling stock)
If you use point detection for block occupation then you need several detectors and additional logic to retain that information. If you use specific trigger detection such as magnet and reed switch then your system fails when unfitted stock is used on the layout.
Greg.P.
Reply to
Greg Procter
And further divided: - Specific item detection, e.g. DCC bi-directional comms (Digitrax transponding or Railcomm), LISSY or RFID - Non-specific (all the rest)
You need to think very carefully about what you want from detection and how the information will be used.
MBQ
Reply to
manatbandq
Well my idea was to indicate the presence of a "train" in a section using secondary current flow through the motor. After that the on/off can be routed via diode isolators to relays/ LED etc for local indication and switching power to provide positive isolation (blocking) between trains. As I use conventional control I am already finding spurious routes (electrical) which indicate TOT when there isn't so I shall probably have to rethink he wiring a tad!
Regards
Reply to
Sailor
If you want whole train detection you will need to add resisters across the wheels of your wagons and coaches.
Chris
Reply to
Chris
It might be simpler to glue some strong magnets below stock and use reed relays on the relevant track sections. Small magnets are really really small, well under 1mm cube being readily available. Or a LED based beam-breaking system trackside (or below track with another part above train)
Otherwise, I'd head down the DCC route, probably with a Loconet (Digitrax based) offering the widest range of options; CML in the UK make a number of interesting boards which talk LocoNet.
- Nigel
Reply to
Nigel Cliffe
I am thinking along the lines of sub dividing each section and using loco only recognition. The movement into each subsection ( irrespective of main section) would then gate a series of subsections in sequence ( the direction can be commanded) this will generate a travelling block which remains open until the tail end sub section of the next occupied section is encountered and power is run down to stop. This should allow two trains to run the same route without fear of collision -- mine always manage this in the most awkward places! This means that each travelling block covers it's own butt end.
Regards
Reply to
Sailor
Place a pair of series diodes (plus two reverse polarity) in each block feed. Measure voltage (1.4v/0v) across the diodes and you have current detection while the controller is above zero. Add HF lighting or just a low current AC bias to your controller output and you have constant current detection. Add axle resistors or interior lighting to your brake vans and you have 'train' detection. Add resistors to all rolling stock and you have full rolling stock detection. etc etc.
Greg.P.
Reply to
Greg Procter
If you just add resistors to the last vehicle (assuming the first vehicle to be electrically powered/reactive) you have the ability to detect the extent of a given train. In point of fact, you are detecting occupation of a given block. It is a reasonable assumption that that occupation is by a train, but it could be something else like a mouse dragging a coin, or a Matchbox car blown by a breeze, or (insert your own ...)
Greg.P.
Reply to
Greg Procter
Reedswitches require modification to make your detection operate. The DCC route still needs blocks for any detection to be relevant.
Greg.P.
Reply to
Greg Procter
Yes agreed, this is the double Tee referred to by Roger Amos. He provides detection under unpowered conditions using a bleed off from the actual detector power supply in parallel to the Loco Controller circuit.
I built one yesterday and it is great on a single length but when offered to my maze of wiring finds lots of alternative paths! I have realised that the only solution is to double insulate sub sections and isolate using double pole switches although I still think that a common rail should be possible but I shall have to ensure that my sub section isolators are on the same line ( difficult with the number of reverse loops which I employ). At the moment our summer is so crap that we still have resident mice but just to show that it is summer they are sharing with the odd lizard. So far the only mouse crime has been to steal the dogs (4 off) special fish jerky treats -- the whole bag full! My track debris usually arises from dead meat flies and spiders.
I am reluctant to load my carriage wheels with pickups as the two which I run with lighting really do have a lot of drag.
Regards
Reply to
Sailor
Use surface mount resistors fixed to the axle and connected to the wheels with conductive paint abd there is no need for extra pickups.
MBQ
Reply to
manatbandq
Now that sounds sensible. I do have a load of these little widgers but quite honestly have never used them. How do they attach to the conductors or PCB come to that?
Regards
Reply to
Sailor
You don't need pickups. Solder a physically small resistor between rim and axle across the isolating bush. One per coach will do for a start and add a second later if that isn't 100% reliable. Best to set up a production line of like wheels and do a good stack at a time :-)
Alternative paths - I guess this is a problem of trying to add detection after it's built, rather than building it in first.
Reply to
Greg Procter
The "problem" is soldering between the relatively tiny end contacts and the relatively large mass of axle and tyre/wheel. Solder the SMD at 45 degrees to the axle with the other pad against the plastic bush and then solder a single strand from tyre to SMD pad. Of course, tinning the axle and wheel surfaces first is a must.
Greg.P.
Reply to
Greg Procter
I assume SMD is = surface mounted device?
Those which I have on a card are said to be resistors and there are also capacitors which look the same. That is to say rectangular blocks. Which are the surfaces to which one solders? I assume the ends would solder onto strip conductors and then break the conductor under the SMD. On an axle therefore it would need insulation (glue?) from the axle to enable conducting paint to be applied to one end already lying on a wheel hub, the other end could then use the axle as you describe. I forsee tyre fitted wire strands getting beaten up in points etc so the paint idea is good.
Blue sky and sun have been seen creeping up on us.
Regards
Reply to
Sailor
Yes.
The two ends are metallised.
See also
formatting link
and google for "resistor wheelsets" and variants thereof. You can actually buy them ready made.
MBQ
Reply to
manatbandq
If you glued the resistor to the axle and use conductive paint to connect each end to the wheels you could do away with soldering altogether.
Regards Jeff
Reply to
Jeff

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