3 aspect model RR signalling help plse

Raiway Pete said:

Even a train with 50 cars in tow on a long block will use up onlz an extra 80 milli amps.

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Also this is only taken from one power supply. With DCC you add boosters. My main unit is 3 Amp, then I can add further 3A boosters where I may be short of current allowing for one loco per block active. Maximum number of blocks on a 3A PS is roughly 5. However if the consist is double/triple headed then that's 2 or 3 of the 5.

Detectors

Angie, Mr Deb,

I guess I made my point. The extra current drain caused by the cars is minimal when compared to the motive power.

As an aside, I see ads on this site for the manufacture of PC boards. Do you guys make your own? I use a film which comes in standard printer size. I just copy a reverse image of the pc board on to it with a laser copier and then just iron the image onto the copper clad surface. I etch in ferric chloride. My foils have a minimum width of about 5 mil. Seems to work and each sheet can provide four 4.5 inch square boards for about a dollar.

Raiway Pete said:

Angie, Mr Deb,
Do you guys make your own? I use a film which comes in standard printer size. I just copy a reverse image of the pc board on to it with a laser copier and then just iron the image onto the copper clad surface.

.....can provide four 4.5 inch square boards for about a dollar.

Click to expand...

I've just started. Using etch resist pen ATM but trying to find someone local with a laser printer. I've got the artwork.

Little bit more expensive here tho', 9"x9" board is about £1.80, but still cheap compared to getting a company to do it

I will send you a printed sheet of Pulsar paper with the pc board printed on it.
If you get the block detector set up then could include it as well.
just iron it on and etch.
Trying the second link you posted (block detection) in TINA. working out why it does not work right. think I have the wiring wrong.
don't know why a resistor is not used for hysteresis? (avoids the circuit from jumping on and off erractically. either on or off)

something not right|??

going to get back to it later. got to get xmas lights, all 15,000 up.
hopfully computer still works

Save this image

Save this attached image. Will write explanation later.

Explanation of Twin-T operation.

Dear MrDeb.

I hope you got the above attachment and made a hardcopy.

The basic Twin-T shows the core of the operation. Basically it consists of two transistors with cross connected emiters and bases. Only one base/emitter junction will conduct for a given current direction. Both transistors however, have their collectors connected to a resistor(R1) and should one of the two base/emitter junctions conduct the resistor/collector junction will tend to drop to the common return. In other words, should the throttle supply a current across the track one of the two transistors (Q1 or Q2 depending on the direction of the current) will conduct.

Notice the presence of R2. This resistor's job is to provide a trickle current to the track should a load be connected across it. This trickle current is enough to get Q1 to cunduct.

So let's look at the "Twin-T with an amplifier diagram. The track being an open connection prevents either Q1 or Q2 from conducting. The collectors are at Vcc. This output is fed to an amplifier transistor Q3, which will conduct - illuminatingthe "block clear" lamp (in this simple case). This is indicated in the "no train" diagram.

As soon as a standing train is on the block with the throttle disconnected, R2 supplies a trickle current to the track va the Twin-T power supply causing Q1 to conduct, thereby dropping the common collector conection to drop to common ground and extinguishing the "block clear" lamp.

When the throttle is supplying current to the engine motor the eastbound current causes Q1 to conduct while the westbound current causes Q2 to conduct. Either transistor conducting causes the "block clear" lamp to be extinguished.

So far so good.

From a practical point of view we really should have some positive logic here. Instead of a lamp we really need a reed relay which is normally OFF. so we take the output of Q3, invert it, debounce it and feed it to another transistor. This is indicated in the lower right diagram on the page. There is also a list of components and quiescent voltage levels at key points.

One note here. Diodes D1 and D2 are two heavy duty devices that can handle 2 Amps. These diodes are connected across the base/emitter junctions (in parallel to the detectors) These diodes bear the brunt of the current should you decide to use signal transistors. These diodes limit the voltage drop across the base/emitter junctions to 0.7 volts preventing Q1 and Q2 from going to transistor heaven. If you decide to use power transistors that can handle 2 to 4 Amps then these two diodes are not needed.

Try it. You might just like it.

Pete

Question for Angie1199

Are you running DC or DCC?

If you are running DCC there are a lot of harmonics generated by the DCC power bus. Harmonics are frequency subsets of the original square wave frequency, and create electronic noise. The Twin-T needs to have a capacitor installed across the detector junctions so that they bypass them. This rounds the corners off enough to prevent False "occupied" indications. It makes no difference to the track power bus and any engine or static decoders.

the pics are really small.
what website did you get them from. I am interested is seeing how this circuit works, Will maybe never build one as I am not doing model rr at this time.

I'm running DCC, 16vac.

Unfortunately I can't read the doc properly as the images are so small.

Aslo the forum rules do say don't upload word documents, use pdf or image filetypes. Hate you to get into trouble.

amazing how small they make the DCC

never got into that level of model rr.
couldn't afford it.
found a very simple and nice descriptive method of block detection.
it explains HOW to assemble a system using prototype boards.
Easy Block Detection and 2-Color Signals, Part 1: Detection Systems and Circuits
that system railway pete is trying to describe was designed back in 1958!!
didn't dawn on me that a DCC system uses AC not DC to control the trains. not familiar with DCC to begin with. get the impression that it is basically remote control using AC to power the locos and then coding the AC signal so each loco has a decoding circuit with is own id per loco.
nice idea.
All I ever did was power the rails with DC and go. One train only. Did get into isolated rails but nothing fancy.

Twin-T diagrams

Dear MrDeb and Angie1199

Yep. I went for the simple stuff too. I found the commercial stuff way too expensive. Today there is stuff that has too many bells and whistles. I found that the Twin-T works fine with DCC. I needed to add a capacitor across the two transistors to get rid of electronic noise and if power is guarranteed to be on the rails all the time then the bleed current resistor (R2) can be omitted.

I recreated the diagrams in a PDF format

See attached.

Try this circuit:

sorry, I think that I've mistaken your post for someone else's.

Old Technology.

Dear MrDeb,

Just a note on old technology. First a tale. I spent 45 years in the computer industry and spent a lot of time and company resources (cash) fixing both software and hardware problems on a world wide basis. One outstanding nugget of wisdom can be gleaned from my illustrious career. Companies are split into "cost" centers". A very noble tenet was to lower costs as much as posible thereby making a division manager one to contend with and a leader of men. Unfortunately the department that took the product over was faced with the extra costs that "cheap" components (read "new and improved technology") imparted upon it. Hence my trip to Rome.

The problem. A subunit periodically went through a power shut down sequence. It was an intermittend problem and I hung around for days waiting for it to happen again. It turned out o be a leaky emitter follower. It was a 2N2222 (Since then it has become a 2N2222A). The company manufactured about 500 of these units. Should a more expensive reed relay have been used the problem would not have occured. So let's do the math. Air fare was around $1500. Italian hotels in Rome are not cheap and I stayed 5 days at $130 per night. Food and other expenses came to about $150. The rented car was $400. (This was in the 70s). My trip cost the company about $2600. Amortize that over 500 units and you get about $5. The reed relay would have cost the company $2 at the most. But because the 2N2222 was only 20 cents someone in manufacturing became a hero.

Linn Wescott's circuit is now over 50 years old. It has proved itself endlessly. It works and it works well. It uses few components none of which are of critical value. And it is extremely cost effective. Trouble shooting is simplicity itself. I try and use transistor sockets so that replacement or testing is simple.

I looked at the site you mentioned and the instructions, history and methodology are superb. The final design however uses chip technology which my fellow model railroaders who are not electronic engineers look upon with abject fear. When it came to actually building such a unit I began to fear the worst. These Radio Shack pre drilled strip boards are designed to be used in a lab where only a "one off" project is required. Those little holes that are evenly spaced all look the same. A jumper one hole off (it's easy to do) means the unit fails the smoke test. A project requiring ten such detectors, I guarantzee, will cause a modeller to tear his hair out in frustration. Troubleshooting a tiny board which has high tech TTL chip technology on board with criss crossed jumpers and components covering each other is NOT the way to go. Angie1199 is doing it right. Once an etch design is in concrete a smooth and seamless production line can be set up.

I have just unplugged a detector driver from my layout controller to check. My detector/debouncer/relay driver uses 14 components consisting of 2 power transistors (I just know that they are two PNP 4 amp devices), 2 2N3906 transistors, 6 resistors, 2 capacitors and a relay with a protecting diode. I have jumpers but they are low profile and don't prevent me from getting at an offending component. These parts occupy less than half of the real estate of a 4.5 inch square PC card.

A final note. If we are talking about a sound decoder on an 'N' scale shunting engine I can understand miniaturization. However the electronics under the layout need not consist of tiny components. Be generous with component real estate on your PC card. There is plenty of room inside that mountain.

Raiway Pete said:

My trip cost the company about $2600. Amortize that over 500 units and you get about $5. The reed relay would have cost the company $2 at the most. But because the 2N2222 was only 20 cents someone in manufacturing became a hero.

Click to expand...

Whilst I see the business logic of stopping expensive trips around the world, you do realise I am just talking about a home model railroad, and not a worldwide business to supply units around the world??

Raiway Pete said:

I looked at the site you mentioned and the instructions, history and methodology are superb. The final design however uses chip technology which my fellow model railroaders who are not electronic engineers look upon with abject fear.

Click to expand...

I'm not so sure this is the case. The project is listed on the NMRA website and other such detectors are listed on other model RR enthusiasts webpages. There is a newer breed of model railroader who have been brought up with technology and they are embracing such new technology. If they are unable to get a circuit working then they also have the access to forums such as this, with people like MrDeb to assist. This is after all why I am on this forum

Raiway Pete said:

A final note. If we are talking about a sound decoder on an 'N' scale shunting engine I can understand miniaturization. However the electronics under the layout need not consist of tiny components. Be generous with component real estate on your PC card. There is plenty of room inside that mountain.

Click to expand...

Oh, trust me I didn't go miniature. 2" x 2 3/4" boards. Components are at least 1/4" apart so I also am able to get easy access. I think I know why I have been having problems tho'. It appears my iron doesn't get hot enough at the tip (alternates purchased) to melt the solder instantly so the heat is on the component too long and hurts the components. I have just ordered a new iron, and hopefully this will fix the issue.

I hope Angie your using a heat snk on all the semi conductors.
I found a sinple paper clip or an aligator clip works great.
USE thin rosin solder as well as extra flux as I described in an earlier post. I use the posin soldering paste from Radio shack. yea its cheap but when your 3 hours away from nearest electronics store.
HEAT the trace pad then apply the solder to the pad not the iron. This may help with your soldering joints hopefully?

Advice for making PC boards

Dear Angie1199,

Yeah I know I ramble on, and I know that your project is not world shattering but I am trying to make a point. That little extra that you spend today will save tons in the future. I had seen the site you mentioned and that is what I was refering to. (OK, your 5 volt power supply went berzerk and burned some of the chips. Try unsoldering a 14 pin device from under some jumpers and components that straddle it -- Yarghh!)

When it comes to PC size and component spacing it's a matter of finger size and heat dissipation. The August 1980 issue of Model railroader "revisits" the Twin-T. The article is very comprehensive and even presents the reader with etch patterns for the 5 component circuit on a 2x4 inch PC board. I hought it was going a bit overboard myself until I had to solder, unsolder, remount and resolder components on my much more compact version. By the way I used an old Commodore 64 to design my PC board. (Just to give you some idea how old I am). I changed my philosphy a bit, gave up on embracing the highest newest technology, made my PC boards larger and became more circumspect about fitting the lowest (and safest) technology to the problem at hand.

MrDeb's idea concerning the filling of spaces between foils is an excellent one. Not only does that make the board more rugged it implies that there is room to make the soldering areas larger. Larger areas imrove post soldering heat dissipation. Cleaning is important too. I can't stress that enough. I use a scouring pad, toothpaste, distilled water and/or alcohol. Then I tin the areas to be soldered. I use a 30 watt iron and apply the tip and some rosin core solder to the end of the component's lead poking through the board. Please don't apply the rosin core solder to the iron tip and THEN to the component lead. The rosin, which acts as a deoxidizer, prevents an insulation layer from forming between it and the copper foil. In the short time between melting and forming a bead and applying it to the area to be soldered it dissipates (in the smoke). This is the prime cause of "dry" soldering joints. Once the bead has formed I then run it down to the (pre-tinned) area. It takes about two seconds. One little tip given to me by an old shop floor technician. Lay the board down for twenty seconds before trimming the leads. Also invest in a pair of side cutting snippers for this. The reason is this. The heat in the component lead travels up to the componet's interior. There the insulation (plastic) keeps it hot a lot longer than that exposed to the air. Using a pair of straight edged snips that "pop" the extra lead off the copper foil sends a pretty powerful shock wave to the allready stressed internal junction of the transistor. Luckily most manufacturers have been using softer alloys for component leads but I have bought transistors that still have those hard metal leads.

Finally a note about the new rail hobbyists. You, MrDeb, myself and very few others that I know like to "make" stuff. Personally I take great pride in making my own scenery, doing my own electrics, laying flextrack etc. etc. But as an editor of MR told me "No one makes PC cards any more". Indeed, indeed. There are few construction articles in magazines that do not use pre-manufactured, plug and play materials. I am living in Slovakia and do not have access to Woodland Scenics, Walthers, or TrainWorld. I have to make do and it's amazing what one can achieve with "on-hand" materials.

Besides, it's fun.

As far as Rail Way petes post, yes use quality parts. nothing wrong with new technology. If old is better then use tubes.
Take for example, you need a flashing signal light. Either use discrete parts, around 10 components I recall or use a 555, with a min of 3 additional components.
now which one is more reliable? having 10 components or 4 components?
Transistors are perhaps the easiest to fail. your posted circuit has 4 per block where as the detector Angie is contemplating on constructing has one semi conductor that unplugs. the TWIN T has a relay that adds to the cost. BOTH circuits are viable circuits but for achieving the same results with improved reliability and lower cost the op amp circuit is the winner hands down.

MrDeb
I'm using a croc clip on the components. Read that somewhere else too. I've got some 60/40 alloy solder. Not sure of gauge but it works fine when the heat melts it. I use that with 'Regular Soldering Paste', lead and acid free. I really do think it's just the soldering iron not getting hot enough. It's an ancient one with cheap metal tips, don't appear to be copper or brass with whatever plating, just solid metal.

I have to say I like the detector circuit on the NMRA site. Not sure how to replcate it in TINA tho' as it needs the track and loco to be simulated. Seems a lot simpler than the original one I was looking at too.

Raiway Pete
I would never say anyone rambles on I like this discussion. I'm learning but also not simply accepting. While it's obvious you have many years building model railways, as I have, I haven't built a project as large or technically advanced as this before. I have never had signalling done automatically so this is a first and even if I may choose a different way to those you suggest or detail, do not think it's a waste of your time. I would rather discuss, then come to a final selection, than simply go off half-cocked and build/create something that I am not happy with in the future.

The roadbed is no-where near completed as yet but once it is then the next things to add are the turnout motors, block detectors and signalling. As all 3 are linked they obviously can't be dealt with individually, and judging by the length of this thread they are a complex subject, so please don't be put off contributing. Even if I may choose a different route others may be reading this thread and could find other ways to their liking.

As you say the magazines now rarely show home made or scrath built items, other than modifications of wagons etc. Buildings, scenery and electrics are generally bought off the shelf.

Signalling pcb here **broken link removed** is rubbish and they're £14.29 each!!! They work on the photocell detector and change from red, to yellow then green 'after so many seconds' which defeats the object. It says it's prototypical but I thought signals changed dependant on presence of a loco, not after so many seconds!

This one, Lenz BM2 Block Section Module (22610) | Antics Online , is more inline with what I am attempting. and for 26 of them, over £1040 is definately not on the cards,

This is the block detector only. Lenz LB101 Current Detection Unit (11210) | Antics Online I mean, £18, for a board that contains parts worth about £3. This is why I build, this is after all rip-off Britain