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DCC combined with Computer Control

Question: I have spent quite a bit of money on my DCC  layout only to discover that Computer Control via my PC would be the next logical step for me. I would like to incorporate Computer Control without abandoning my DCC hardware. Do you have any suggestions?  Mel, New York City

Over the past few years Computer Control of model railroads has been developed, particularly the Digital Command and Control (DCC) type.  The following paragraphs discuss Computer Control techniques from various manufacturers:

o CTI Electronics

o JMRI

o Digitrax

CTI Electronics of Baltimore, MD is a developer of model train Computer Control software (not free) and associated interface hardware  that will permit your DCC model train layout  to run your trains and associated model railroad accessories using an IBM Compatible Personal Computer (PC).  Basically with the CTI scheme your present manually operated control panel is replaced with your PC screen.

Of course your PC screen with the help of CTI software and an array of  hardware control and sensor modules which  CTI refers to as Train Brains becomes a rather sophisticated train control panel. Each CTI electronics Train Brain is daisy chained into a communications network which is connected to your computer’s COM or USB port.   See Figure below.

With the Train Brains it will be possible to control various railroad functions turnout control, track signal control,  detect and display train position, and detect and display turnout position, just to name a few.  In addition there will be true interaction between track signals, train speed and direction providing true model train speed control.

Train Brain sensor modules are compatible with various types of sensor components such as Infra-Red, Photo cell and Current Detection.

The CTI Smart Cab Hardware Module provides a pop-up throttle display onto your PC screen integrated with other Train Brains effects in lieu of using your own  DCC controller (Throttle). Effectively will you will have accomplished the building of your own model railroad DCC controller.

If you have a DC layout with blocks that are used to operate more than one train on a track, also lends itself control via the CTI Smart Cab Module.

You can also use your own DCC throttle for parts of your layout operation and Smart Cab for the remaining sections.

In other words, use your DCC throttle without Smart cab and limit your Train Brains for turnout control, etc. for semi-automatic operations. Again the computer will interface with the model railroad turnouts using the USB or COM ports.

Visit the CTI website for additional and more detailed info.

To date, CTI Electronics software supports the following DCC controllers:

o   Power House Pro and Power Cab series from North Coast Engineering (NCE)

o   System One from Wangrow Electronics

o   DCS-100 and Zephyr from Digitrax

o   Easy-DCC system from CVC

o   XPress Net from Lenz

o   V2x- Bus based on command stations from Lenz

o   Master command station from ATLAS

o   Train Master Command Control (TMCC) from Lionel

o   Marklin Digital System from Marklin

It is also possible to mix CTI hardware and software with other vendors.

Visit the CTI Electronics site for additional information.

JMRI

JMRI which stands for JAVA Model Railroad Interface is Freeware comprised of the following applications:

o JMRI DecoderPro

o JMRI PanelPro

o JMRI Tools

o JMRI LocoNet Tools

JMRI DecoderPro

DecoderPro software is free and is compatible with the following operating systems: Windows, Linux, Macintosh (OS 8.6 through 9.2 and MacOS X), and OS/2.

JAVA must also be available as well as a serial interface, either on the computer itself, or via a USB adapter.  You also need to have a serial connection to your DCC system for your DCC computer interface. For more information, reference the DCC hardware pages on the JMRI website.

DecoderPro performs the following functions and provides the following attributes:

Programs Configuration Variables (CVs) into a locomotive’s decoder without using your own DCC command station. Can also be used to program stationary decoders. Much more user friendly than typical DCC command station.

Configured using text files, can be adapted to additional decoder types.

Create a Roster of every locomotive you have depicting detailed Configuration Information for the installed mobile decoder.

Communicates to decoders using JMRI programming interface, compatible with most computers and layout hardware.

Open Source code, can be changed.

JMRI PanelPro

Panel Pro performs the following functions and provides the following attributes:

It is used to create front panels on your PC screen. This is accomplished in two ways:

o  Panel Editor will allow you to make a drawing of your track layout with icons representing turnouts, etc.

o Layout Editor will allow you to develop the logic for the icons, such as turnout position appearing when icon is clicked upon.

Other Handy JMRI Tools

SENSORS – Tool permits interface with your layout’s sensors to provide the sensor’s output, for example train position to be displayed on replica of track layout on PC screen. Other items like semaphore operation is another item that can be displayed.

TURNOUTS – Used to control and display  turnout position via PC screen, on track replica or used for semaphore operation, etc.

THROTTLE – Used to create a graphical throttle interface on PC screen.

CONSISTING –  Used to control more than one locomotive to pull the same train.

SIGNALS – Provides signal head control, lamp colors as a function of train occupancy detection sensors, train speed, etc.

LIGHTS – Provides lighting for control panels as well as scenery.

ROUTES– Permits the development of canned program scenarios to set up a complete set of actions and reactions on a train layout by one command, such as turnout control, in addition to others.

LROUTES – This tool is an extension of the ROUTES tool to include lights and signal heads.

LOGIX – Permits the model railroad hobbyist to set up logical conditions on the layout.  For example, train direction and presence using model train block occupancy must be detected prior to operating a crossing gate.  The tool is user friendly. The need for expressing himself with mathematical terms is not required.

FAST CLOCKS – Fast Clocks are used in model railroading to simulate the faster passage of time which makes the train on the layout appear to run longer distances.  In particular, this tool develops an internal fast clock using your computer or it can interface with an external clock provided by other DCC system vendors such as Digitrax or NCE.

SPEEDOMETER – The tool calculates and displays the train’s scale speed.  Of course it is based on the train being detected as it passes motion sensors.

ENGINE SPEED MATCHING – Used as part of the Consisting process previously mentioned.

SCRIPTING – In the world of computer programming, a script is a program or sequence of instructions that is interpreted or carried out using another program rather than the computer processor, (as a compiled program is).  JMRI scripts use Python, a popular general-purpose computer language, which will be used to control the model trains.

AUDIO – This tool controls sounds that are played back by your PC.

ID TAGS – This tool creates Identification Tags (ID Tags) for many items on your layout, for example, rolling stock.  With the use of sensors the tool can track rolling stock position and report the time the stock was last observed.

LocoNet Tools – These tools have specifically written to interface with the Digitrax LocoNet specific hardware devices such as the PR3 which will tie in to the computer via the USB  interface port  to the Digitrax DCC model train controller.

The purpose of the above explanations was to give you an idea of the JMRI tool suite. More detailed information is available on the JMRI website.

Digitrax

Digitrax manufactures the following hardware products that are used for computer control:

MS1oo is a RS232 Computer Interface device

The PR2 is an interface device which allows Digitrax SoundFX locomotive decoder users to download new Project sound files and even reflash the decoder’s firmware for latest updates.

The PR3  is also an interface device but is different from the PR2 in that it offers a USB 2.0 interface,  selectable MS100 mode, and is priced lower.

MS100

  • The MS100 Computer Interface allows computer with an IBM compatible COM, or RS232 communications port, to monitor Digitrax LocoNet.

 

  • See Figure below:

  • For example, an application from either CTI Electronics or JMRI Panel Pro would display a control panel to include a replica of the railroad layout on the computer screen. The software messages received via LocoNet and the MS100 will indicate block occupancy, signal state and other information generated by detection devices attached to LocoNet port. This is how the DCC system can detect train location.
  • Ofcourse the programming details can be found on the CTI Electronics website or JMRI website.
  • For IBM compatibles with only a 9 pin male DB9 type COM port connector, you can use a DB9(female) to DB25(male) adapter commonly sold in electronics.  Make sure you are connected to the correct COM port and that you have it set up as required to match the settings needed by your CTI Electronics software.
  • For the latest Computers which have a USB Interface another type of adapter is required. Ses figure below.

PR2 SoundFX Decoder Programmer performs the following functions:

In conjunction with SoundLoader software the PR2 allows the hobbyist to substitute different locomotive sounds into a Sound Project file.

Digitrax also has a website (Digitrax Sound Depot) which can be used to download Sound Projects.  Your Sound Projects can also be uploaded to other model train hobbyists.  Link to the Digitrax Sound Depot for more detailed information.

See Figure below:

There is an alternative hook-up for the PR2 which uses a USB port adapter if required. See following Figure:


 The PR3 is slightly different than the PR2 in that it is compatible with a USB 2.0 interface, has a selectable MS100 mode and is priced lower than the PR2.  The PR3 also provides the USB/LocoNet connectivity for third party software such as JMRI, Railroad and Co., and others.  See Figure below:

Here is another device that is good for third party software usage. It is called the Loco Buffer-USB and is another way to interface between a Digitrax DCC Controller and a Computer’s USB port.

It is manufactured by RR CirKits, Inc. 7918 Royal Ct. Waxhaw, NC 28173

See figure below for typical hook-up.

 

 Reference to link www.rr-cirkits.com for hardware and software compatibility.

The previous scheme can be expanded to include the addition of  CTI hardware and software for control of a typical group of  CTI’s Brain Train devices. See figure below.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

 

Digital Command Control (DCC) for Model Trains

 Model railroading and specifically model train control is in the process of changing drastically from the past.  Digital Command Control (DCC)  for railway modelers  replaces the Alternating Current (AC) and Direct Current (DC) power controls previously used.  It fundamentally contains a Digital Command and Control station, which replaces the AC Model Trains Transformer or DC power pack that is used in the non-digital or analog world.

The DCC controller generates a digital signal packet, which is capable of communicating with several locomotives on your model train layout.  Each locomotive contains a decoder, which has its own address thus limiting its response to only when the DCC controller sends out the locomotive’s address. A digital instruction code follows the address which controls the locomotive’s speed, direction, sounds, and lighting effects just to name a few. The DCC controller provides these commands via the model train track rails. There are also DCC controllers that are wireless, permitting the operator to walk freely around the model train track layout at the same time. As required, in order to provide adequate current to run several locomotives at once, a Booster device is added to amplify the DCC current.

In addition to locomotive control, DCC digital signal packets can also be used to control stationary devices such as turnouts and other model train accessories in a wireless fashion.   This is a big breakthrough in the model trains hobby. See the following figure, which depicts a typical digital signal packet:

DCC Signal Packet Waveform


If one were to monitor the electrical signal across the train rails with an oscilloscope, the following characteristics should be noted:

1)      The waveform is Bi-Polar with its voltage varying between + 14 volts and – 14 volts. It is symmetrical about zero volts.

2)      It is Pulse Width Modulated in such away as to provide a digital command to the locomotive’s decoder or other device containing a decoder.

3)      It is not a periodic waveform, meaning it does not repeat itself as an AC signal does.

4)      The National Model Railroad Association (NMRA) in association with its DCC Working Group is in charge of the design and manufacturing standards for DCC equipment.  Basically this group controls the critical elements of the electro-mechanical design of a DCC  manufacturer’s products.  Details of these standards can be found on the NMRA website.

5)      The DCC timing and protocol defined by the NMRA and DCC Working Group defines signal levels and timing between the command station and the track.  However, these protocols are combined with a variety of proprietary standards from several manufacturers.  In other words, command stations from one manufacturer might not be compatible with throttles from another.

It should be noted that many manufacturers of model trains have gotten on the DCC bandwagon such as:

Bachmann Trains and train sets

Lionel Model Trains and train sets

Model Power

LGB Trains

Hornby (UK Company)

Kato

MTH Trains

Walthers Trains

Atlas

Athern Trains

Broadway Limited

Rivarossi Model Trains

The above manufacturers will generally supply locomotives that are DCC ready (Have  internal wiring and NMRA compatible connector without Mobile Detector) or DCC installed (Has Mobile Detector installed).  In addition, locomotives are available with or without Sound Decoders.

DCC is basically model train scales independent.  Hence, whatever your interest whether it is HO, O, N, or G scale model trains, you should have no trouble entering the world of DCC. Even Z scale model trains and on30 scale which are not as popular can be operated with DCC.

Another interesting aspect of DCC is its adaptability to computer control. Go to the following link for more information: DCC combined with computer control

DC Locomotive using DCC Controller

It is also possible to run a DC analog locomotive (non-DCC Type) at the same time as a DCC locomotive.  This is accomplished by assigning the DC analog locomotive an Address of 00.  This address will cause the DCC waveform to have what is known as a zero stretched waveform which is basically either a plus DC  voltage to cause the locomotive to move in one direction or a negative DC waveform to cause motion in the opposite direction.  However, because the DCC waveform still has periodic bits ( AC-like voltage swings), some DC motors begin to hum and heat-up while at idle (locomotive not moving).  Therefore, caution is recommended if one tries this technique.

DCC Model Train Wiring Requirements

With DCC operation, it is possible to control many trains simultaneously on the same track. Hence your controller or booster must have the capability of shutting down in the event of a short. Hence, the wire size chosen must not only be capable of supplying several trains, but it must also be capable of turning off the controller or booster if a short is detected at the greatest distance from the booster or controller . The following table depicts the primary track bus wiring vs scale used.

The Track Bus is typically wired to a Terminal Block along with the feeder wires. The smaller size feeder wires are soldered to the rails.  Rule of Thumb – Feeder wires are usually 1 to 3 ft in length and are usually  3 to 6 ft apart.  The following table depicts the feeder bus wiring vs scale used.


Direct Current (DC) and Alternating Current (AC) Differences

If a locomotive is of the Direct Current (DC) variety it will likely use 2 rails instead of  3 as used with the Alternating Current (AC) Lionel Trains.

The table below provides a breakdown of locomotive AC/DC power requirements vs scale.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Refer to the following for additional information associated with Digital Command and Control units for model trains for every scale such as HO, O, N, and G :

Digitrax

Lenz

Loy’s Toys

Zener Diode

 

 

What is a Zener Diode?: A Zener diode is a special case of  ordinary semiconductor silicon diode.  Specifically, the Zener displays the following property: The direction of current is from positive to negative and it blocks current in the minus to plus direction (Reversed Bias). See sketch for Zener diode symbol and picture of markings on a part itself. If a positive voltage is applied to the anode terminal of a Zener diode and a negative voltage is applied to cathode terminal, the Zener diode will behave as an ordinary semiconductor diode.  However, when a positive voltage is applied to the negative, the Zener diode will breakdown when it is reversed biased by a voltage greater than the breakdown voltage. As a result a Zener voltage (Vz) will appear across the diode terminals, with its cathode being positive and the anode being negative.See Figure below for pictorial and associated symbol:

See example below for more information

In the preceding figure which reflects a zener diode acting as a zener voltage regulator across load resistor R2.

There is a + 12 vdc voltage source.

There is a 9.1 vdc output voltage requirement from the zener

Total Current passing through R1 = I total

The current through reversed biased zener  = I zener

The required load current is passing through  = I load

Important Considerations:

1) Diode Voltage = 9.1 vdc +/- 10%

2) Zener diode voltage must be several volts below the source voltage in order to force the zener into its breakdown region (9.1 vdc).

3) The Zener maximum power rating must never be exceeded. In order to achieve this, R1 must be selected first, in order to limit the current through the Zener. This is calculated with the R2 load disconnected.

Case 1 Details using 1N4739 1 watt Zener diode (reference zener diode data sheet available on Internet):

This Zener voltage which appears across the zener terminals is very stable, hence it is used a relatively inexpensive zener voltage regulator or voltage reference. The Zener voltage is steady over a wide range of input or output load variations.

Given the following:

1) Test Current  = 28ma = Best operating Zener Current (available from zener diode data  sheet for the 1N4739)

2) Load requires 10ma based on device that is across the 9.1 vdc zener

Calculations:

I total = I zener + I load          Kirchoff’s Laws

or

I total = 28 ma + 10 ma = 38 ma.

R1 resistance value = Voltage across R1/I total     Ohm’s Law

or

R1 = 12-9.1 = 2.9 vdc/38 ma = 76.3ohms

9.1 volt Zener has a 1N4739 part number. Data sheet indicates that the maximum power rating = 1 watt.

Maximum Zener Current = Max Power/Zener voltage

o r

1 watt/9.1 vdc = 110 ma  with load R2 disconnected.

With R2  removed, Zener power = 9.1vdc x 28ma = 254 milliwatts

This choice of diode is perfectly safe even with a 10% variation of voltage tolerance and subsequent power change we are still under 1 watt.

Case 2 Details using BZX79-C9V1 500 mw Zener diode (reference zener diode data sheet available on Internet):

Given the following:

1) Diode Voltage = 9.1 vdc +/- 0.1 vdc

2) Test Current  = 5ma = Best operating Zener Current (available from data  sheet for the BZX79-C9V1)

3) Load requires 10ma based on device that is across the 9.1 vdc zener

Calculations:

I total = I zener + I load               Kirchoff’s Law

or

I total = 5 ma + 10 ma = 15 ma.

R1 resistance value = Voltage across R1/I total       Ohm’s Law

or

R1 = 12-9.1 = 2.9 vdc/15 ma = 193.3ohms

9.1 volt Zener has a BZX79-C9V1 part number. Data sheet indicates that the maximum power rating = 500 mw.

Maximum Zener Current = Max Power/Zener voltage

o r

0.5 watt/9.1 vdc = 55 ma  with load R2 disconnected.

With R2  removed, Zener power = 9.1vdc x 5ma = 45.5 milliwatts

This choice of diode is perfectly safe even with a +/- 0.1 vdc variation of voltage tolerance and subsequent power change.


Conclusion: Either the Case 1 or Case 2 diode will meet the max power specification for the selected diode, but the Case 2 diode is much more accurate voltage-wise.

The Battery voltage source to the Zener diode can actually be a variable or fixed voltage power pack  whose DC voltage is three to five volts greater than the Zener’s voltage.

Another Application

A Zener diode can be used as an overvoltage protector for the output of a power supply that experiences an unwanted voltage surges, as long as the zener voltage is less than the power supply output. When the voltage across the power supply spikes up, the zener across the power supply output will absorb the spike and limit the voltage output to equal the zener output.  Further explanation is beyond the scope of this tutorial.

What are Power Zener Diodes? As the name implies, Power Zener Diodes can take alot more power dissipation.  For example these diodes are available in the 22 to 39 vdc range with currents as high as 50 amps. They are obviously used in high powered power supply applications and in automobile alternators as rectifier diodes.  Not much application to model trains but if your interested take a look at Diodes, Inc. at www.diodes.com

A Surface Mounted Zener Diode is one that is mounted directly to a Printed Circuit Board (PCB)  without the use of wire leads attached to the diode which in turn are fed through holes in the circuit board.

Zener Diode Testing

There are two methods.

(1) The first way is using just an ohmeter.  If the diode is in the 2.4 volt to 12 volt range set the meter to the 10kohm scale. Put red probe on cathode and black probe on anode and the meter needle will go towards full scale. If you reverse the probes with red probe to the anode and black probe to the cathode you should measure about 2 to 4 ohms using a lower scale. By the way if you read zero ohms in both directions the zener is shorted or if if both readings are full scale on the 10k scale, then the zener is blown open. Some zeners will read other values other than 2 to 4 ohms, but what is important that you get less than 100 ohms (red/anode to black/cathode) and a much larger reading (greater than 10k red/cathode to black/anode).

(2) The second way is to test the zener in a dynamic fashion by creating a circuit similar to either case 1 or 2 above, with the load resistor removed. However, the zener must be put in series with a current resistor on the order of 5k. Then measure the voltage across the zener and determine adequacy per data sheet.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Connecting Zeners in Series

Rather straightforward, if two zeners are hooked up (cathode to anode + cathode to anode) the two voltages will add up.

Connecting Zeners in Parallel

Putting Zeners in parallel creates a situation where one will turn on before the other and draw all the current, thereby negating the effect of the second Zener.

In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

LED Lights

 

Definition: LED Lights or LED  Bulbs are actually Light Emitting Diodes (LEDs) possess all the properties of a conventional semiconductor  diode described in another section which passes current in one direction with the additional property of emitting light. The direction of current is from positive to negative. See sketch for diode symbol and picture of markings on a typical LED.  The top sketch is a schematic symbol for the LED. The arrow on the diode symbol indicate direction of current flow. The LED has a positive and a negative terminal. The positive LED lead is known as the Anode. The negative terminal is known as the Cathode. The small wiggly arrows above the main arrow represent light being emitted. The lower sketch represents what the LED physically looks like. It has two leads emanating from the base of the LED. The long lead is the positive lead (Anode) and the negative lead (Cathode). The LED resembles a miniature light bulb that comes in several colors red, green, yellow, orange, etc.

In the figure below (CASE 1) the LED lights up because the current is permitted to flow from plus to minus. In the second part of the figure (CASE 2) the LED is blocking the flow of current. Note that when using an LED it is necessary to always use it with a series resistor (R1) in order to limit the current flow to a safe value. For example, if the LED specification is rated at 2 vdc @ 20 ma, then the Battery voltage of +12 vdc will provide +2 vdc across the LED and the remaining voltage will be 10 vdc across R1 as per Kirchoff’s Law and the current thru the circuit will be calculated per Ohm’s Law as follows: R1 = Voltage/Current  which equals 10vdc/20ma =  500 ohms.  The Power value at R1 = I squared x R = 20ma squared x 500 = 0.2 watts. Therefore, R1 we should use a 500-ohm ½-watt resistor.

Typical LED Applications to Model Train Layouts

Track Signal Lighting– With the proper interface circuitry to provide the Track Turnout position, LEDs draw a fraction of the current of the average incandescent bulb with the advantage of long life on the order of 100,000 hours. For this application the following would be applicable: red led lights, green led lights, or yellow led lights. The size of the leds 1 mm,  3 mm, 5 mm, etc. would be a function of the specific application to the railroad model train scale being used.

Passenger Car Lighting– As a minimum it is possible to add LED lighting with some very simple circuitry which uses the track voltage as the source. It is also possible to install a regulator in each passenger car with an output capacitor to virtually eliminate interruptions caused by passenger car wheel pick-up bounce. Internal lighting is best accomplished with 5 mm LED lights (clear) while tail lighting is best accomplished with the smallest possible red LED lights. The Internet is a good source of schematic diagrams for these applications.

Model Building Lighting– One of the most important applications of LEDs is for Model Train Scenery associated the lighting up of the model buildings used in your layout. Again as with other applications, low current draw and long life provides model railroad LED lighting a real advantage.  Of course the LED must be surrounded by some sort of painted plastic shade to soften the generally bright LED light.

Additional Locomotive lighting can be added such as Ditch lights with associated circuitry. More about that in future articles.

Control Panel Lighting – The following figure depicts a model railroad control panel whereupon red and green LED’s are used to show model train turnout position. Another section discusses how to construct a model railroad control panel with LED lights that denote turnout control and position.

Control Panel Lighting For Railroad Yard– The following figure depicts a control panel whereupon green LEDs are used to show chosen path for train to enter. It is accomplished by wiring several LEDs in series to depict turnout positions as well as the track(s) being used.

How to wire LEDs in series – In the above Control Panel several Green Leds were wired in series to depict switch path that is to be by train. For example, we wish to illuminate 3 Leds in series and we are using a + 12 vdc battery or power supply. Just as before we have to calculate the value of resistor R1.

For example, if the LED specification is rated at 2 vdc @ 20 ma, then the Battery voltage of +12 vdc will provide +2 vdc across each LED and the remaining voltage will be (12-6) vdc across R1 as per Kirchoff’s Law and the current thru the circuit will be calculated per Ohm’s Law as follows: R1 = Voltage/Current  which equals 6vdc/20ma =  300 ohms.  The Power value at R1 = I squared x R = 20ma squared x 300 = 0.12 watts. Therefore, R1 we should use a 300-ohm 1/4-watt resistor.

The following figure shows how a small portion of the Yard Panel would appear using 3 LEDs for one track path and a single LED for an optional path. Notice that a third Power Supply, PS #3 is used because the Yard might not be physically located near the Main Panel.

 

LED Rope Lighting – This type of lighting which is comprised of a string of lights can be very handy to place under your layout table. This will be very handy to use when troubleshooting wiring problems.

In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/

For more detailed  information on Model Railroad Projects utilizing LEDs, navigate to the following links:

Turnout Indication LED Projects

Model Railroad Fire Engine LED Project

Model Railroad Crossing Flashing LED Project

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Diodes

Definition:  A Diode is a semi-conductor silicon device which passes current in only one direction. Think of it as a one way valve. It is constructed of a semi-conductor material similar to transistors. It has two terminals, positive and negative.  The direction of current is from positive to negative. See sketch for diode symbol and picture of markings on a typical diode.

Simple circuit demonstrating diode action:

In the sketch on the left, the diode is oriented so that current from the 12 volt battery can flow to the lamp thus permitting the lamp to turn on. In actuality there will be a small voltage of  0.6 to 1.7 volts when conducting.

In the sketch on the right, the diode is oriented so that current from the 12 volt battery cannot flow to the lamp thus preventing the lamp from turning on.

Diode Applications

Notice in the figure below that the diode passes only the positive part on the sine wave, thus creating a relatively poor positive only dc power supply.  The resulting dc value is also shown in the sketch. This process is known as ½ wave rectification.

Notice in the above circuit how the diode combination passes the positive and the negative part of the sine wave, thus creating a relatively positive only dc power supply which is better than the previous example.

During the positive half of the sine wave the current will pass from the source through diode #1 , through the load and then through diode #2. During the negative half of the sine wave the current will pass from the source through diode #3, through the load and then through diode #4.

The resulting dc value is also shown in the sketch. The process is known as full wave rectification. In practice, as part of power supply design, a capacitor is often added across the load to provide a dc voltage with minimum variations or ripple.

There are many types of diodes which have many applications in the model train world such as the following:

Light Emitting Diodes (LEDs) possess all the properties of a conventional semiconductor  diode  described in another section which passes current in one direction with the additional property of emitting light.   Refer to the following link for more information:  Light Emitting Diodes

A Zener diode is a special case of  ordinary semiconductor diode.  Specifically, the Zener displays the following property: The direction of current is from positive to negative and it blocks current in the minus to plus direction (Reversed Bias).  If a positive voltage is applied to the anode terminal of a Zener diode and a negative voltage is applied to cathode terminal, the Zener diode will behave as an ordinary semiconductor diode.  However, when a positive voltage is applied to the negative, the Zener diode will breakdown when it is reversed biased by a voltage greater than the breakdown voltage. As a result a Zener voltage (Vz) will appear across the diode terminals, with its cathode being positive and the anode being negative.   Refer to the following link for more information: Zener Diodes

Infrared Diodes  are different regular LEDs in the following ways:  They do not give off visible light. They have a lower forward voltage and a higher rated current.   Infrared Leds are used in remote control devices.  In the world of model railroading use Infrared hand held wireless throttles and wireless receivers.

Bridge Rectifier Diodes are comprised of a package of four diodes configured as described in a previous paragraph associated with full wave rectification.  They are available in various voltage and current ratings.

Switching Diodes as the name implies are used  in switching and logic networks.  The 1N914 is an example of such a diode.

High Current Diodes  as the name implies are used  in high voltage power supplies, 6 amps to 100 amp range.

Schottky Diode has the following properties: Low Forward Voltage Drop = 0.15 to 0.45 volts when conducting. Typical Voltage Drop for regular semi-conductor diode=0.6 to 1.7 volts when conducting .  High switching action.

Laser Diodes have the following properties: Transmits analog or digital signals for sending through optical fibers via a very tiny beam.

High Voltage Diodes  as the name implies are used  in high voltage power applications,  10kvolts max

The Infrared Laser Diode is similar to the Laser Diode except it is based on the gallium arsenide compound in the 750 to 900 nanometers wavelength in the infrared spectrum or the indium gallium phosphide in the 1200 to 1700 nanometers in the infrared spectrum.

A Surface Mounted Diode (smd diode) is one that is mounted directly to a Printed Circuit Board (PCB)  without the use of wire leads attached to the diode which in turn are fed through holes in the circuit board.

A Current Regulator Diode is similar to a zener diode except that it regulates current over a wide voltage range.

In general, the following vendors are recommended for any of the above electronic components:

Radio Shack local store or at www.radioshack.com

Futurlec at www.futurlec.com

DeMar Electronics at www.demarelectronics.com

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

 

Transformers

One of the most useful devices that rely upon the Mutual Inductance effect is the Transformer. The Transformer is capable of transforming energy from one circuit to another without a direct connection. It is comprised 2 coils of wire wrapped around an iron core. The input coil is known as the Primary and the output coil is referred to as the Secondary. Electrical energy (voltage) is supplied to the primary causing a change in magnetic field at the iron core. The magnetic core enhances the mutual inductance between the coils. This causes an electric field, which induces an output at the secondary. The transformer is an alternating current (ac) device only. See sketches  below.

Top sketch is a physical representation & the bottom one is the schematic representation.

Mathematical Relationships associated with Transformers –

The input voltage to the primary and the output secondary voltage relate as follows:

Vsec = Vpri multplied by (Nsec/Npri)  where:

Vsec = the secondary output voltage

Vpri = the primary input voltage

Nsec = number of turns in the secondary winding or coil

Npri = number of turns in the primary winding or coil

Example:

If  Vpri =120 vac;

Nsec = 100 turns;

Npri = 10 turns;

Then Vsec = 120(100/10) = 1200 vac

Note that if  in the above sketch we can consider the Secondary as a Primary and vice-versa, we get inverse results. In other words 1200 vac input will result in 120 vac output.

The input current to the primary and the output secondary current relate as follows:

Ipri = Isec  (multplied by (Nsec/Npri)  where:

Isec = the secondary output current

Ipri = the primary input current

Nsec = number of turns in the secondary winding or coil

Npri = number of turns in the primary winding or coil

Example:

If  Isec = 1 amp

Nsec = 100 turns

Npri = 10 turns

Then Ipri = (1)(100/10)  =10 amps

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

In the Model train hobby, Transformers can be used in lighting applications as a source of voltages.
Point Of Interest:  The Lionel O gauge trains use a power pack which contains a transformer of the variable type.

In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/

Inductance

In the figure below, when the switch is closed, the battery produces an electric current, which induces a magnetic effect or field.   The red line in the figure depicts the magnetic field.  If one were to take a magnetic compass, which faces North-South in the direction of the earth’s magnetic field, and place it next to a wire that is carrying a current, the compass needle deflects away from its North-South orientation.

 

Likewise, if one would replace the compass with another coil, the second coil would respond to the magnetic field created between the 2 coils which in turn would cause a voltage at the terminals of the second coil. See above sketch:
This above phenomenon are examples of Inductance. More specifically, the voltage at the second coil in the bottom figure is created by Mutual Inductance.

Inductance It is measured in henrys: symbol, L

Typical values of Inductance are either in millihenrys mH (one thousand of a Henry) or microhenrys uH (one thousand of a Henry).

Inductors in Series –

In the following figure, two Inductors are in series.  When two inductors are in series the total inductance exclusive of  Mutal Inductance = L1+ L2  measured in henrys.  Now if  the coils are close enough physically, the magnetic fields that the coils generate will interact causing a Mutual Inductance.

This must be accounted for by stating that the total inductance = (L1+M) + (L2 + M) or (L1-M) + (L2 – M) which can be rewritten as Total Inductance = L1 +L2  +/- 2M where M is the Mutual Inductance which depends on whether or not the coils magnetic fields aid each other (+)  or oppose each other (-). 


Inductors in Parallel –

In the following figure two Inductors are in parallel.  When two inductors are in parallel the total inductance exclusive of  Mutal Inductance = 1/L1+ 1/L2  measured in henrys. 

Now if  the coils are close enough physically, the magnetic fields that the coils generate will interact causing a Mutual Inductance (M). This must be accounted for by stating that the total inductance = 1/(L1+M) + 1/(L2 + M)

or 1/(L1-M) + 1/(L2 – M)  where the Mutual Inductance (M)  depends on whether or not the coils magnetic fields aid each other (+)  or oppose each other (-). 

Typical values of Inductance are either in millihenrys mH (one thousand of a Henry) or microhenrys uH (one thousand of a Henry).

Model Train Applications

(1) Manufacture of relay coils which can be used to throw turnouts or switches to control train direction, or select electrical signal paths. Basically the inductor surrounds a magnet. As the coil is energized with a voltage, the magnetic field will cause the magnet to move, thus causing electrical contacts to move. It is a way from converting electrical energy to magnetic and then to mechanical motion.

(2) The inductance caused by long wire runs that cross higher voltage runs can play havoc with a train layout. In other words a 115 vac wire run can cause interference if  it  is within a couple of inches from a digital low level set of pulses.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Capacitors in Series and Parallel Circuits

Example of  Three Capacitors in series:

The total value of the above capacitors in series is equal to 1/C1 + 1/C2 + 1/C3.   In the above sketch the symbols for the capacitors represent polarized capacitors. The  curved line of each capacitor is the negative plate. The straight line  is the positive plate.

Example of  Three Capacitors in parallel:

 

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

In general, the folowing vendors are recommended for any of the above electronic components:

Radio Shack – Local Store or on-line at www.radioshack.com

Futurelec at  www.futurlec.com

Capacitor

The term Capacitance refers to an electrical phenomenon whereupon an electric charge is stored.  In the following figure a Capacitor is shown comprised of two metal plates separated by a small distance. When the switch is closed, the battery will cause plate number 1 to be positively charged. Conversely plate number 2 to be negatively charged because of electrons being repelled from the negative battery terminal to plate number 2.

In the above circuit,  an electric field is established between the plates, even though there is an air gap.

 In the construction of a Capacitor, the air gap is usually replaced or combined with other solid or thin-filmed dielectrics. The dielectric is actually the insulation material that is used between the plates.   The dielectric material selected is a function of the circuit application.  In general the name of a capacitor describes the dielectric being used. There are capacitors (electrolytic types) which filter ac ripple in a DC Power Supply.  Electrolytic and tantalum capacitors are always labeled and are polarized.  The Ceramic, mylar, plastic film, and air capacitors are not polarized and therefore their leads need not be marked.

Capacitance Units

 Capacitance is measured in units of farads, however most practical values of capacitors are in microfarads, abbreviated as uF.

 The uF is equal to one-millionth or 1/1,000,000 of a farad or E-6 farads  in E Notation or E-6F

A capacitor 0.47 uF can also be written as 0.47/1,000,000 or 0.47E-6 in E Notation.  Capacitance can also be specified in pico farads or 1 millionth of a microfarad.  In other words 1 pico farad = E-12 farads or E-12F.

Model Train Applications

Capacitors are not just used in DC power supplies but  are an integral part of many electronic circuits. Many electronic schematic ciruit diagrams and associated parts lists are available to the model train do-it yourself  hobbyist  in magazines and on the internet to perform special functions like crossing gate comtrol,  etc.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics


In general, the folowing vendors are recommended for any of the above electronic components:

Radio Shack – Local Store or on-line at  www.radioshack.com              

Futurelec at  www.futurlec.com

Definition of Power

Power is defined as the rate of doing work. It is calculated by the following formulas:

 1) P = V x I whereupon:

     P= power measured in watts

    V= voltage measured in volts

     I = current measured in amperes or amps

 2) It can also be expressed as P = I squared x R whereupon:

    P= power measured in watts

    I = current measured in amperes or amps and then squared

    R= Resistance in the circuit of interest

 3)  It can also be expressed as P = V squared divided by R whereupon:

      P= power measured in watts

     V = voltage measured in volts and then squared

     R= Resistance in the circuit of interest

 It should be noted that formulas 2 and 3 are derived from formula 1 by algebraic solution.

A volt-ampere (VA) is the unit used for the apparent power in an electric circuit, equal to the product of root-mean-square (RMS) voltage and RMS current. In direct current (DC) circuits, this product is equal to the real power (active power) in watts. Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents).

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

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