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Topics: 16   Replies: 16
posted on Mar 10, 2018:

A positive DC offset of several Volts triggers the horn/whistle on O-gauge conventional control. Any engine with a horn/whistle has this detector circuit built-in. And there are after-market boards or upgrade modules with same detector capability. You can roll-your-own DC offset detector for less than $1 in parts. And if the application of DC offset detection is to simply flash alternating LED ditch lamps, you can integrate both functions for another $1 or so. There is a lot of tedious component-level assembly.

Two wires on the left bring in AC track voltage. When DC offset is detected, the two white LEDs (3mm diameter suitably sized for most diesel engine ditch lights) alternately flash.

In action:

The trick, if you can call it that, is to isolate or separate the DC offset from the 60 Hz AC voltage. You are trying to find a few volts of DC in the presence of 18V or more of AC. The filtering of the 60 Hz is a simple Resistor-Capacitor filter shown above using a 100K resistor (R5) and a 4.7uF capacitor (C4). This is a simple 1-pole filter with a time-constant of RxC = 100k x 4.7uF = 0.47 seconds. This is equivalent to a so-called corner frequency of 0.3 Hz. Such a filter will knock down the 60 Hz AC track voltage amplitude by some 100 times. So the 18V AC gyration are become less than a 1/4 Volt which in effect leaves just the DC component of the track voltage. This filtered detector voltage triggers a pair of transistors set up in a so-called Darlington configuration which essentially turns on when its input exceeds about 1.2V DC. When the Darlington-pair turns on, it provides 5V DC power to a widely used oscillator circuit which flashes a pair of LEDs.

The circuit uses readily available, low-cost components available in thru-hole or surface-mount packages depending on your preferred assembly method. C4 should be non-polarized uch as a ceramic or bipolar type.

If the 2 input wires are reversed to the track, this circuit would flash the LEDs when the Bell button is pressed - that is, when a negative DC offset of several Volts is impressed on the AC track voltage.
Alternating ditch light flasher for conve...
Topics: 43   Replies: 59
posted on Mar 4, 2018:

Thought I would like to build a model of a Garratt locomotive next so I went searching for some photos of them on the internet.

Being mostly ignorant of equipment used on railroads in foreign countries, I had thought that this type of locomotive was only used in Great Britain and that they only made one style of this locomotive.
Boy .. was I in for a surprise .....

I quickly realized that the Beyer-Garratt steam locomotive was used all over Europe and some of them are still in regular use in Australia and Africa.
They were built as small as a wheel arrangement of 0-4-0 + 0-4-0 all the way up to 4-8-2 + 2-8-4.
Here are a few photos starting with the smaller locomotives and going to the bigger ones.

They also show up in a variety of colors.

Some photos of a couple of the locomotive that are still in operation.

SO .... after spending some time looking at photos of them and seeing some of them running on Youtube, I started digging up parts to start building my model and this is what I have to start with.

These are parts of two European 0-6-0 locomotives that are plastic models made by Pola Maxi in Germany.
They are suppose to look like this but my two models have seen better days.

I'm going to build a 0-6-0 + 0-6-0 so I stripped the two models down to the basic chassis by removing the side rods and valve linkage and the steam cylinders.
The steam cylinders are the wrong design and the side rods and valve linkage are all plastic so I'm not going to use these parts.

The Garratt locomotive has a front and rear set of drive wheels with the water tank sitting over the front set of wheels and the coal tender is over the rear set of wheels.
The boiler is mounted on a carriage frame work that is hung between the two sets of drive wheels.
Each set of drive wheels has the steam cylinders at the far end of the chassis and it pivots at the other end where the boiler is mounted over the end set of wheels.

The first problem that I see is the electric motors on the plastic models is in the cab with the steam cylinders at the front.

I can't make the pivot mount for the boiler carriage on the opposite end from the cylinders because the electric motors are there.
So I need to mount the steam cylinders on the end with the electric motor so it will be hidden inside the water tank and the coal tender and the carriage for the boiler can then pivot on the other end of the two chassis units.
( Whew ... I hope that wasn't too confusing ? )

Back to my old standby of parts for building plastic locomotives, I'm milling the top off a steam cylinder from the Rivarossi 0-8-0 locomotive kit.

The tops are milled off both steam cylinders and I'm gluing a piece of styrene on top of them.
The individual parts are shown in the foreground and the piece of styrene is clamped onto the cylinder in the back ground, waiting for the glue to dry.

The next problem is the plastic models have the center drive wheels connected to the steam cylinders and the Garratt locomotives have the far end drive wheels connected to the steam cylinders so I need to switch the wheels.

The crank pin and eccentric lever are made from plastic on the model so I have to make new crank pins out of steel rod for the rear drive wheels.

The steel crank pins are made up and pressed into the drive wheels.

The center wheels and the end wheels have been switched and the crank pins are pressed into the end drive wheels.
The other two pairs of wheels have the crank pin hole threaded so I can screw a small shoulder screw into them to hold the side rods in place.

So far .. I have a pair of 0-6-0 chassis units, steam cylinders that will fit them now, brass valve linkage ( That I think I can make work ) and the main rods for the steam cylinders.
I wasn't able to find any side rods in my parts that will fit the wheel spread on these two chassis.

So I'm going to machine the side rods out of some strips of brass.

The side rods are finished and mounted on the two chassis.

The steam cylinder is mounted on the end of the chassis with two small screws and the electric motor is set in place.
The main rod is set into the guides on the cylinders and on the crank pin to see how everything fits.

The top of the chassis frame on these drive unites sits about 1/4 inch higher than the top of the frames for the 0-8-0 locomotive kit.
I had to mill out the underside of the steam cylinders where they sit on the top of the frame so that the cylinders sit down low enough to line up with the wheels.

So the support for the cross head guide rails has to be milled out so that it sits lower on the frame also.
The support on the left is the stock unit and the modified support is on the right.
The two little white blocks on each side is where the holes were drilled for fastening this to the front of the valve linkage frame with two small screws.

The front part of the brass valve linkage assembly has to be shortened in order for the front linkage arms to reach up to the steam cylinders and the rear linkage arms to fit back to the rear wheel.

The stock brass valve linkage assembly is on the left with the stock cross head guide support in front of it.
The shortened valve linkage assembly is on the right with the modified cross head guide support attached to the front of it.

Seeing as how the steam cylinder and guide support had to be lowered for them to fit .. you would think that I would have realized right away that the valve linkage is probably going to have to be lowered also ....
Well I didn't think about that until I had everything assembled on the chassis and got right down at eye level to take this photo.

It was then that I saw that the pivot point at the end of the front linkage arms is still sitting higher then the slide bracket on the upper part of the steam cylinders.
This pivot point on the front linkage arms is suppose to rest in the pocket of the slide bracket on the cylinders.

Oh well ... I'll chalk this one up to brain fade and go on from here . ......
I took the brass valve linkage assembly all apart so I could reassemble it with the side frames upside down.

With everything put back together, the pivot point of the front linkage arms now fits snugly into the pocket of the slide bracket on the steam cylinders like it is suppose to.

The valve linkage assembly with the cross head guide support mounted to the front of it is attached to the top of the chassis with two screws.

A matching pair of drive chassis's.

I have left the electric motor off the chassis unit so I can rotate the wheels by hand to make sure that everything works correctly and they won't be put back on until after everything is painted and the locomotive is assembled for the last time.

I'm going to use this frame and floor piece from the tender of the Rivarossi 0-8-0 locomotive kit to build the carriage frame that is mounted in between the two drive units and carries the boiler.

The two parts are clamped together while the glue dries.

Then I milled off the parts for the brake system.

A piece of styrene is mounted on the end of each of the drive units and a counter-bored hole is machined into them for the pivot point with a brass ring set into each of pivot holes.
A round boss is glued onto each end of the underside of the carriage frame that will fit into the counter-bored pivot holes.

Styrene is glued onto the top of the carriage to bring it out to the correct width.
The carriage frame is set on the drive units.

Beyer - Garratt locomotive
Topics: 16   Replies: 16
posted on Feb 25, 2018:

As of February 2018, the MTH website continues to show the use of an NTE50 latching DPDT relay to control a Tortoise switch machine from an AIU SW(itch) port.


The suggested relay is now obsolete and even when in production was quite spendy (over $25). The required functionality to operate a Tortoise switch machine via the AIU's SW(itch) port is a so-called LATCHING DPDT (double-pole-double-throw) relay. Suitable "bare" or loose unmounted relays can be had for just a few dollars but require soldering and such. There are assembled DPDT relay modules with screw-terminals but are around $15 each.

Here's a DIY method for about $5 out-of-pocket and does not require soldering to tiny relay pins. Additional ports would be less the $3 out-of-pocket as a single 12V DC power adapter can power multiple (at least 10) ports.

Again, this method does require careful attention to detail and is perhaps more of a thought-provoking idea than a practical solution. In any case, here's the concept in action ... albeit driving a bi-directional DC motor rather than a Tortoise switch machine.

Note: using this method, when the relay module is first powered, it always starts in the "OFF" or unlatched position. This can be wired to be the "straight" or "diverge" position. The point being this is different than a true mechanically-latching relay which remembers its position between operating cycles. There are features within MTH DCS command-control to set multiple SW ports to a pre-determined configuration.

Note: DPDT relay is used to reverse (invert) the polarity of a DC voltage to the switch machine DC motor. If AC voltage is available to drive the switch machine(s) then only a single-pole SPDT relay is required. This method is described in the Tortoise literature. A latching relay is nevertheless required. In this case, Relay #3 can be the SPDT relay and Relay #4 is not used.
Tortoise switch machine control using MTH...
Topics: 16   Replies: 16
posted on Feb 25, 2018:

MTH DCS Accessory-Interface-Unit (AIU) provides 10 each SW(itch) ports and ACC(essory) ports. You cannot reconfigure an SW port to be an ACC port or vice versa. So if you use up all 10 ACC ports and need one more, it doesn't matter that you have any spare SW ports - buy another AIU for >$100 (MSRP).

Here's a way to get ACC port functionality from an SW port for about $5 out-of-pocket. Additional ACC ports after the first are less than $3. The user-interface will be arguably unconventional in that you will press the SW port "diverge" button to turn ON the accessory, and the SW port "straight" button to turn OFF the accessory.

The star of the show is the 4-channel, non-latching 12V DC relay module for less than $3. Only 3 of the relays are used to make a latching relay that is "set" when the diverge button is pressed, and reset when the straight button is pressed. The wiring is somewhat tedious but it is what it is. Here it is in action.

The $2 12V DC power supply can supply at least 10 modules so each additional ACC port only requires just the 4-channel relay module. Since only 3-channels are used per "new" ACC port, some wiring and space can be saved using 8-channel or 16-channel relay modules. These modules have similar less than $1/relay pricing. The relays in these modules start in the OFF condition so, like an AIU, the ACC port will be OFF when you power on the TIU/AIU.


The wiring of the multi-channel relay module is somewhat tedious to say the least. Another idea is to use a so-called bistable relay. On each trigger, a bistable relay alternates (toggles) between On and Off. So unlike the previous method which has 2 inputs (set and reset), the bistable method has a single input (toggle) which alternates between ON and OFF. So rather than pressing "diverge" to turn ON and "straight" to turn OFF, you press "diverge" to turn ON, then "diverge" again to turn OFF, then "diverge" again to turn ON, and so on. The "straight" button has no effect.

And here is is in action.

Perhaps obvious, but the downside of this method is you can't directly or absolutely set the Accessory to ON or OFF. You can only alternate between ON and OFF with each button press. This may be a non-issue since you might be watching the Accessory and can visually see it operating (or not). In any case, with the bistable relay, the relay itself starts in the OFF condition when you first turn on the AIU for an operating session.

As with the latching relay method, a single 12V DC power adapter can supply 10 or more bistable relay modules so the cost for each additional ACC port is less than $3 out-of-pocket.

The particular bistable relay module shown can be doubled up such that a single SW port can create 2 "new" ACC ports.

MTH AIU: make an ACC port from a SW port
Topics: 16   Replies: 16
posted on Feb 25, 2018:

Roll your own or purchased 4-wire 3-aspect LED signal heads typically use common "+" or common-anode wiring. Published circuits such as the reverse-engineered MTH timed-yellow method for 3-LED Red-Yellow-Green do not use the common "+" wiring.

The circuit can be modified with additional components. While the component cost is only a few dollars, the assembly and soldering can be tedious.

3-aspect timed-yellow circuitry also applies to PRR 7-LED style where the center LED is always ON. In both styles, the "+" DC supply to the LEDs has a single current-limiting resistor. For 12V DC operation, a typical resistor value for 1-LED-at-a-time heads is 1000 Ohms (3-LED-at-a-time heads 330 or 470 Ohms).

A low-cost "Delay ON" relay module from eBay can be used which in many cases can eliminate the need to turn on the soldering iron!

A signal head is typically driven by a 2-output occupancy detector such as the MTH ITAD or Lionel 153IR. The timed-yellow circuit provides the 3rd-output.

In any case, the occupancy detector must provide 2-outputs which even for the basic insulated-3rd-rail method will have a relay output with the "NO" and "NC" being the 2 outputs. Here's an example of the same delay-ON relay module providing timed-diagonal to a 3-aspect 7-LED 4-wire PRR-style head.

DIY 4-wire 3-aspect timed-yellow signal h...
Topics: 68   Replies: 116
posted on Feb 21, 2018:

Small roadside diners like this one were common. The 'home cooked' food was great at some, not so great at others. They were given various nicknames - the Greasy Spoon, The Beanery, etc. This modified Plasticville diner occupies a lot at the Highway 5 grade crossing on the Baltimore & New York.
The Beanery
Topics: 16   Replies: 16
posted on Feb 5, 2018:

This rainy-afternoon project was more for amusement than something practical I'd expect anyone else to try. But this might spawn other ways to apply low-cost Arduino and similar DIY microcontrollers and remarkably inexpensive (99 cents) servo mechanisms which easily attach to Arduino modules.

For conventional O-gauge operation, I am not aware of any inexpensive method to smoothly vary AC track voltage under remote control. Typical applications might be to automatically decelerate or accelerate a train approaching or departing a station. Or to automatically adjust track voltage to regulate speed as a train ascends or descends a grade.

I say "smoothly" vary because there are several write-ups on using the string of back-to-back diode method to provide discrete voltage steps...some even using relays under Arduino control to sequence a stair-step of voltages selected from a diode string. The diode string method is simple and inexpensive but is also inefficient from a power standpoint. The standard method for varying AC voltage in most low-end O-gauge controllers (Lionel CW-80, MNH Z-controller) is the semiconductor triac. But it takes specialized knowledge to control triacs from an Arduino.

On the other hand, making a servo motor turn from one angle to another is as simple as a single command using the standard Arduino servo library. So why not just use a servo motor to turn the knob of a Z-controller. Note that in the video a $1 servo-exerciser is used to generate the magic pulse-modulated commands that the 3-wire servo requires.

The Arduino can emulate a DIRECTION change by momentarily commanding zero track voltage.

And since even the entry-level Arduino comes with 2 servo outputs, the obvious next step would be to use a 2nd servo to control whistle/horn and bell. The trick is the buttons on a Z-controller are spaced such that a single servo can activate both!

Multi-button sequences of Horn and Bell can trigger special functions in some O-gauge engines as demonstrated at the end of the video. For example, a controller that is sensing where a train is on a layout can know to activate a short-short-long warning when approaching a grade crossing.

Servo control of MTH Z-controller transfo...

O Gauge General Categories:

Electronics & Wiring (62)
   Alternating ditch light flasher for conventional control
Electronics & Wiring (62)
   Tortoise switch machine control using MTH AIU SW Port
Electronics & Wiring (62)
   MTH AIU: make an ACC port from a SW port
Electronics & Wiring (62)
   DIY 4-wire 3-aspect timed-yellow signal head
Electronics & Wiring (62)
   Servo control of MTH Z-controller transformer voltage, horn,...
Electronics & Wiring (62)
   Modifying a 99 cent servo for continuous rotation
Electronics & Wiring (62)
   Post war 3 rail relay blook
Scratch Built Rolling Stock (7)
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