Instructions for wiring the Model Scenery Signal Driver to control 3 aspect block signals.

The instructions in this page cover:

• Common Cathode and Common Anode connected LEds.
• Normal and Approach Green Signals
• Three Light Normal Four Block Loop
• Three Light Approach Block Loop
• Connecting Occupancy Detectors To The 3 Light Signal Circuit

The image to the left shows the Model Scenery Signal Driver

You can get the parts necessary to make this Signal Driver here .

Instructions for assembling it are here.

Other Signal Types

• Red, Yellow and Green – 3 Light signals.  Click For Instructions
• Red, Yellow and Green And Red Green – 1 Light Spotlight signals. Click For Instructions
• Red and Green – 2 Light signals.  Click For Instructions
• PRR Position Light signals. Click For Instructions

Circuit Diagrams

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.

 

 

Normal Or Approach Green Signals

The signal drivers can be connected for NORMAL or APPROACH lighting of the GREEN signal. These schemes are shown on other diagrams on this page.

NORMAL 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 Lighting means that the GREEN signal is only on when the block before a particular signal is occupied and thus 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 the Normal GREEN lighting configuration.

See the 4 BLOCK, NORMAL GREEN and 4 BLOCK, APPROACH GREEN diagrams below for an illustration of these functions.

General Notes For The 3 Light Signal

Some of the notes below require that the changes be made when assembling the board.  The instructions are here.

•   The signal circuits can be controlled by any device that can pass at least 1 milliamp current and shares a common connection with minus terminal of the signal circuit’s power supply.
•   The circuit is designed for a 12 volt power supply voltage and will drive light emitting diodes at approximately 10 milliamps. Other supply voltages and LED currents can be used.
•   The values of the current limiting resistors for the LEDs – R4, R6 and R8 – can be changed to achieve the desired brightness from each signal LED. For example;- If the signal LEDs are too bright, external resistors can be connected at the circuit board’s outputs rather than replacing resistors R4, R6 and R8 on the circuit board.- If the signal LEDs are too dark, resistors R4, R6 and R8 can be replaced with resistors of lower value.
•   Diodes D1 and D3 at the base circuit of transistors Q1 and Q2 provide an extra voltage drop in the base circuit that allows the transistors to turn off completely. This diode is not needed at the base of Q3.
•   The combined current from a DETECT INPUT of one block and the YELLOW INPUT from the previous block is about 2 milliamps. This low current allows the PNP signal circuit to be controlled directly by optoisolators.
•   The circuit’s BOD input will operate at properly at voltages of less than 3 volts.
•   More than one block can be controlled by a single input device if diodes are used to separate block input devices such as occupancy detectors, toggle switches and computer control systems.
•   The signals can be controlled by a dispatcher using toggle switches. In this case no occupancy detectors would be needed.The toggle switches can be used in conjunction with block occupancy detectors.
•   Common cathode and common anode connected LEDs can be used for different blocks so that various home built and commercial signals could be used at the same time.
•   The circuit can be adapted to drive 2 colour, common cathode connected or common anode connected LEDs to make a Search Light type signal. Diode D2 is removed from the circuit for this application.

 

Three Light Normal Four Block Loop

Three Light Approach Block Loop

 

Common Cathode And Common Anode Connections

 

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 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.

 

Using Diodes At The Occupancy Detector Inputs

The next diagram shows how diodes can be used at the BODinputs 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.

 

 

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.

Feedback

If need any information, have comments, or have questions, please use this spam free form.