Railelec, Model Railroad Electronic Projects

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Railmodel Electronics A collection of Simple electronic Projects for the Railroad Modeler

Š 2020

This book presents a number of electronic projects for the railroad modeler who wants to enhance the layout and add more realism without a lot of expense. Projects in this book will use readily available components and simple circuits that can be assembled without needing to understanding a circuit schematic diagram or to find special printed circuit boards. Project Index on next page

Some of the projects were originally presented in the NMRA ‘Scale Rails magazine’ Train Position Detectors

Using a CdS cell with LED output A Short Track Break - with Opto output

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--------------------------------------------------Utility Power Supply

A Resistor selectable voltage - from the DCC supply

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Using a computer Hi current, multiple voltage power supply Click Here ---------------------------------------------------

Timing Circuits

Basic timer IC

- 555 description of operation

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Basic flasher - Utility circuit, DCC powered

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FRED rear end LED - with optional power sources

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--------------------------------------------------Automatic Operations

Automatic Turnout and Reverse Loop controller

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A Train Shuttle controller for DC power

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An Intermediate signal - DC track signal with power control

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Single Line control/acquisition signaling

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- Linked Departure signals Flashing yellow signal aspect

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Grade Crossing Signals

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--------------------------------------------------Other circuits

Simple CAB for Yard or other motors

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Servo motor controller for points or semaphore signals

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Carriage Lighting for all scales

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So it doesn’t work and you have checked everything. Go here and follow the help steps - see pages 4 & 5

To Railmodel.design Home

The these page links go to a web site for description and build pages. There is a return link to this book. Each project links to a Components list where suppliers part numbers are listed. Page 2

To Construct these Circuits. You will need some soldering skill which is easy to pick up with a little practice. A number of internet web sites can be found with instructions and advise on the equipment needed. A cheap volt/ohm meter would be a help if things don't work as they should. Each project will show a picture of the finished item, a graphical representation of the components in place on the circuit board, a diagram of where the copper strips on the underside of the board are to be cut and for those who can read them, the schematic diagram. You will find assembly instructions with each project as well as optional changes to modify the performance. If the instructions and diagrams are followed carefully then a going project should result. If not turn back to the index page and follow the trouble shooting procedure link. Component links go to suppliers, links and part numbers to order from them.

Soldering is no big deal but many people are put off by it. There are only three things to remember: • Clean metal surfaces • A flux to make the solder flow • Solder to cover the copper and wick up the component lead. Clean the copper before you do anything to it. If it has been around for a while it will have a tarnish on it so use steel wool to brighten it up. Similarly the component leads, if they are not new may need to be burnished or scraped with a blade before soldering. The Solder Wire used for electronic work has a flux in the center of the solder and this is usually sufficient to cover the immediate area of soldering. Some will be left and spill over to the between tracks area but can be washed off with solvent when finishing the job. Put the 25 watt or similar iron with a pencil bit to the component lead and the copper strip together, count two and push the solder wire into the heated area and iron tip. It should melt immediately and flow out over the copper and the lead. Pull the iron up the component lead so extra solder does not spill over to other copper tracks. If the iron is not hot enough or too small a wattage it will lose heat to the copper and the solder will take a second or two longer to flow. The iron tip should have a covering of clean solder but not an excess which will spill onto the copper. If the work is not clean the solder will not flow and will form a blob on the component lead. Page 3

Some considerations and basic procedures 1. Get out the magnifying glass and carefully check each copper strip for solder spill overs to adjacent strips or across copper breaks. 2. Running a craft knife blade along the gap between the strips also helps to locate spillover solder.

3. If you have a multimeter check the +12 input to Ground The resistance should be high, you could also meter between the copper strips for unseen shorts. There will be shorts if link wires connect the strips, so check for them. 4. Do a visual check of the components and link wires for position, polarities and the values. 5. Diodes transistors and capacitors are polarity sensitive so check that they are the right way round. A reverse connected capacitor or diode will draw a lot more power and overheat, even explode after a few minutes.

If you are certain that there are no faults then it is time to apply the Power . Again a multimeter is good value. 1. Connect the meter to plus and minus points in the circuit and apply power if the voltage is not what it should be then there is a Problem. 2. If no meter then the only sign of a fault might be a component getting hot and smelling, or even worse smoking. 3. If you have no meter then put a 21 watt car bulb in series with the power lead. If it comes on then investigate and find what is drawing so much power. With no wires, components or soldering out of place then the circuit should be working. Time to connect it into the layout or a test setup. If not working then it is time to understand the schematic and with a meter check for realistic voltages across the various components. If you get half the voltage you expect and it is a timer output then the output may be oscillating rapidly between on and off.

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TROUBLE SHOOTING A.. Use a magnifying glass to check for potential short circuits - Look along the gaps between the copper - is there any solder bridging the gap. B.. Trim component leads and link wire ends - Are any of the component or link wires bent across the gaps C.. Finally check with a knife - run a knife blade along the gaps to find whisker of solders D.. The cuts in the copper strips. - check that they are all cut right through. - A meter is a help here. E.. Are components etc in the right place - double check the component positions - is the component polarity correct - are the copper cuts in the right place F.. Meter for these power problems - check plus and minus power input for shorts - check all ground connections are made - check all plus power connections are made - check that IC pins go to the correct component Finally.. - it should be safe to apply power for a few seconds - do LEDs power on? - no smell of something heating up Now.. Power on again and measure with a meter the voltages on some of the obvious components, IC pins etc. If all look more or less correct you probably have a going circuit Page 5

Chapter 1A Page 6


The Photo resistor, sometimes called a Light Dependent Resistor (LDR or CdS cell), should have a light on resistance of about 1,000 to 5,000 ohms. They are sensitive to visible light and can be packaged in metal cans or encased in moisture resistant epoxy.

Adjustment:Set the 20K potentiometer at about half way and with the photo resistor covered (Dark) by whatever you are sensing, adjust the potentiometer so the LED is on at the brightness you want. Uncover the photo resistor and the LED should go off. If not readjust so the LED is less bright.

Installation:The photo resistor needs a moderately strong ambient light to reduce its resistance to a low enough value. If there is not enough light where you want to Operation:place the detector then a small The light shining on the photo bulb will need to be installed to resistor makes its resistance low shine on the cell. You could mount which makes a low voltage on the this low down to the side of the transistor base (b). This is passed to rails and shine it up across the the emitter (e) but will not be space that the train will pass sufficient to light the LED. When the through and on to the photo photo resistor is covered its resistor mounted above and on the resistance increases to a high value, other side of the rails. A shield or gives a higher voltage on the emitter tube could be put over the light to and current stop it being visible from the side. flows from the collector  to the LED. Many other means of getting light To operate reliably a 3 volt battery is to the detector could be devised. needed. A multi-output Plug pack, 3 to 12 volts unregulated DC could be used in place of the battery. The circuit will work up to 12 volts from a DC power supply but care is needed in the adjustment as the LED could be burnt out at the higher voltage.



If you are using a battery, the current drain of this circuit will be about 0.25 milliamps per detector, which should give it several months operation on 'D' cells. However you will probably have several detectors running through a tunnel or along a hidden yard and supplied by the one battery so a power on/off switch would be advisable.

Construction:The components can be mounted on a piece of strip board (vero board) and can be fitted into a 4 hole by 10 hole area - see diagram. The picture shows the CdS cell mounted on the vero/strip board but it can be on flying leads somewhere on the layout and the LED and PCB mounted on a convenient track side panel. Multiple PCB's and LED's could be mounted side by side as they are very small.

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