3 Light - Model Railroad Signal Driver

  The 3 Light type model railroad block signal circuit that has been designed to produce solid - Red, Yellow or Green signal aspects. The signals can be connected for NORMAL or APPROACH type lighting of the Green signal.

Printed circuit boards and parts are available for this circuit.

email

  If you are interested in printed circuit boards please send an email to the following address: rpaisley4@cogeco.ca Subject: 3 Light Signal

3 Light Signal Driver Features

The Circuit Can Be Used To Drive

  For2 Colour, Position Light and Search Light type signals.


Block Diagram And Schematic For The 3 Light Signal Driver

  A block diagram symbol is used to represent the PCB schematic on block connection diagrams. The following diagram shows the block diagram and the circuit that it represents.

  The terminal placement on the block diagram matches the terminal placement on the circuit board.


Test Circuit Schematic


3 Light Signal Connections

Red, Yellow or Green

  This is the basic circuit for common cathode and common anode connected LEDs for a 3 Light Signal.

  Any number of signal blocks can be connected in series. To be able to show all of the aspects the protected track section should be at least four blocks long.

  The signal blocks can be wired for NORMAL or APPROACH lighting of the GREEN signal. These schemes are shown on other diagrams.

  NORMAL - Type Lighting means that the GREEN signal is always lit unless the signal is changed to YELLOW or RED by one of the circuits inputs.

  APPROACH - Type Lighting means that the GREEN signal is on only when the block after a particular signal is showing a RED signal. The Green signal is on when Terminal GI is LOW. The YELLOW or RED input functions are the same as for Normal GREEN lighting.


3 Light - Common Cathode LED Connections

Connected In A Four Block Loop



3 Light - Common Anode LED Connections

Connected In A Four Block Loop



General Notes For The 3 Light Signal


Connecting Occupancy Detectors To The 3 Light Signal Circuit

  The 3 Light Signal Driver circuit can be controlled by many types of input devices including most Block Occupancy Detectors designs as well as toggle switches and the outputs of computer system interface cards.

  For BODs with open collector transistor outputs, the signal circuit and the BOD can use the same power supply and must have a common connection at the minus of the power supply.

  Computer system interface cards usually have open collector transistor outputs. The interface card can have its own power supply but will need a common connection at the minus of the power supply of the card and the signals circuit.

  BOD's and interface cards with optoisolator outputs can be used directly and do not need to have a common power supply connection.

  A dispatcher can control the signals by using toggle switches to control the signals as shown on the block diagrams. In this case no occupancy detectors would be needed but they could be used in conjunction with the switches.

  See the Using Isolating diodes At The Occupancy Detector Inputs section later on this page for more BOD input information.



  The signal circuit can also be controlled by the VT-5 Block Occupancy Detector that can be found at this site.



Circuit Board Options And Prices


  The 3 Light Signal circuit boards are 2.0 inches by 2.0 inches. They are commercially made and have been tinned.

  All external connections to the PCB are made via 3.5mm terminal blocks.

  LEDs for the signals are not supplied with the circuit boards as the LEDs used depend on the scale and the user's preferences.


  3 Light Signal circuit boards sold = 785.

OPTION 1 - Circuit Boards Only

 1 to 4 - 3 Light Signal circuit boards without parts are 3.50 dollars us each, plus postage.

 5 to 10 - 3 Light Signal circuit boards without parts are 3.00 dollars us each, plus postage.

 11 or more - 3 Light Signal circuit boards without parts are 2.75 dollars us each, plus postage.


OPTION 2 - Assembled Circuit Boards

 1 - Assembled - 3 Light Signal circuit board is 9.00 dollars US, plus postage.


OPTION 3 - Circuit Board With All Parts

 1 - Kit - 3 Light Signal circuit board with all parts is 7.50 dollars US, plus postage.


OPTION 4 - Circuit Board Without Terminal Blocks

 1 - Kit - 3 Light Signal circuit board without terminal blocks is 5.00 dollars US, plus postage.


email

  If you are interested in printed circuit boards please send an email to the following address: rpaisley4@cogeco.ca Subject: 3 Light Signal



3 Light Signal Parts List

Qty   Circuit Part Number   Part Description   Digi-Key Number
3 - Q1, Q2, Q3 - IC TRANS PNP SS GP 200MA TO-92 - 2N3906FS-ND
5 - D1, D2, D3, D4, D5 - DIODE SWITCHING 75V 500MW DO-35 - 1N4148DICT-ND
3 - R1, R2, R3 - RES 100K OHM 1/4W 5% CARBON FILM - 100KQBK-ND
3 - R4, R6, R8 - RES 1.0K OHM 1/4W 5% CARBON FILM - 1.0KQBK-ND
3 - R5, R7, R9 - RES 10K OHM 1/4W 5% CARBON FILM - 10KQBK-ND
1 - C1 - 1.0uF 50V Radial capacitor - P5174-ND
4 - Terminal Blocks - 2 Position - TERMINAL BLOCK 3.5MM 2POS PCB - ED2635-ND
1 - Terminal Blocks - 3 Position - TERMINAL BLOCK 3.5MM 3POS PCB - ED2636-ND

3 Light Signal PCB Parts Placement Diagram

Circuit Board Parts Placement Diagram

Print the diagrams to aid in assembling the circuit board.


Bidirectional Signals For Single Track

With Tumble Down Interlocking

  Four blocks of opposing direction signals are show in the next diagram.

  Directional interlocking (Tumble Down) of the signals is included so that the opposing direction's signals can be manually or automatically be forced to RED while the scheduled movement has normally operating signals. The interlocking and all of the diodes can be omitted if not needed.

  Two diodes have been added at each signal's BOD input to separate the BOD inputs from the interlocking circuits.


Using Diodes At The Occupancy Detector Inputs

  The next diagram shows how diodes can be used at the BOD inputs of the signals to provide more complex signal schemes. The diodes allow separate input devices to control more than one signal while isolating the BODs from each other during normal operation.

  A possible use for diodes at the BOD inputs is at a rail crossing or interlocking where tracks that do not have the right-of-way would have their signals held at RED by the dispatcher until the crossing is clear.

  A diode matrix circuit could be used to create complex signal control systems.




Other Signal Light Arrangements


2 Colour Signals

Red and Green

  The 3 Light Signal circuit board can be used to control two aspect, Red and Green only signals. No modification is needed to the circuit board and the inputs, except for yellow, retain their functionality.

There is no YELLOW aspect for the 2 colour signals, however, diodes can be added to the BOD inputs that will cause the empty block behind an occupied block to show a RED signal. This is illustrated in the lower schematic on the next diagram.

  The number of blocks held at RED can be extended by using more diodes.


PRR - Position Light Type Signals

  The 3 Light Signal circuit board can be used to drive a PRR - Position Light type signals. No modification is needed to the circuit board and the control inputs retain their functionality.

  Approach signal lighting is possible for position light signals but it is more difficult to achieve.


3 Colour Signals Using Common Cathode Or Anode LEDs

Red, Yellow and Green

  The 3 Light Signal circuit board can drive common 3 lead, cathode and common anode connected bicolour LEDs used in a searchlight type signal head.

  Diode, D2, is removed from the circuit so that the Green LED remains ON when the YELLOW input to the signals goes LOW.


High Current Adapter For Larger Lamps

  The 3 Light Signal circuit board can control high current lamps such as automotive lights by adding transistors to the signal outputs of the circuit.


PNP - 3 Light Model Railroad Signal Circuit Page.

556 - Bipolar LED - Searchlight Signal Circuits Page.

Colour Shifting for Bipolar LEDs

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

email

  If you are interested in printed circuit boards please send an email to the following address: rpaisley4@cogeco.ca Subject: 3 Light Signal

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20 February, 2017