556 - Searchlight Signal Circuit (2016)

For Red & Green - Bicolour LEDs

  This circuit controls a single head Searchlight, or Target, type signal and can produce a solid - RED, YELLOW or GREEN indication. The signals can be configured for NORMAL GREEN or APPROACH GREEN lighting of the signal.

 - 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 lit only when the block before a particular signal is showing a RED signal. The GREEN signal is on when GI Terminal is LOW. The YELLOW or RED input functions are the same as for Normal GREEN lighting.

Printed circuit boards and parts are available for this circuit.

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556 - Searchlight Signal Driver Features

The Circuit Can Be Used To Drive

  This circuit uses a LM556 - Dual Timer IC in a complimentary output configuration to drive a red and green, bipolar type light emitting diode to produce the signal's three colours.



Searchlight Signal Driver Complete Schematic

For 1 Block

  The following schematic shows one signal circuit schematic with all of the components needed for Normal or Approach Green Lighting of the signal.


Complete Circuit Board - Multiple Block Connections

Normal Or Approach Green Lighting

  This following diagram shows five signal blocks using complete circuits.

  Complete circuits can be used for either NORMAL or APPROACH Green lighting of the signal.

  Any number of blocks can be connected together.

 



Partial Circuit Board - Multiple Block Connections

Normal Green Lighting Only

  If Approach Lighting is not needed, the parts associated with this can be left off of the circuit board and Q1 replaced with a jumper.

Partial Circuit Board - Multiple Block Connections

Normal Green Lighting Only

  This following diagram shows five signal blocks using partially assembled circuit boards.

  Partially assembled circuit boards can only be used for NORMAL lighting of the GREEN signal.

  Any number of blocks can be connected together.



General Notes For The 556 - Searchlight Signal Driver Circuit


Connecting Occupancy Detectors To The 556 - Searchlight Signal Driver Circuit

  The 556 - Searchlight 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 often 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 556 - Searchlight Signal Driver 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 556 - Searchlight Signal Driver circuit boards are 2.0 inches by 6.0 inches and contain 3 complete block circuits. Each circuit board has 3 complete signal circuits on it.

  The boards are commercially made and have been tinned.

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


Click On The Picture For A Larger Image.



OPTION 1 - Circuit Boards Only

 1 - 556 - Searchlight Signal circuit board without parts is 12.00 dollars US each, plus postage.


OPTION 2 - Assembled Circuit Boards

 1 - Assembled - 556 - Searchlight Signal circuit board is ?.00 dollars US, plus postage.


OPTION 3 - Circuit Board With All Parts

 1 - Kit - 556 - Searchlight Signal circuit board with all parts is ?.00 dollars US, plus postage.


OPTION 4 - Circuit Board Without Terminal Blocks

 1 - Kit - 3 Light Signal circuit board without terminal blocks is ??.00 dollars US, plus postage.


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


Circuit Board Parts Lists For One Circuit Board

Parts For 3 - Normal Or Advance Green Block Circuits

Part Qty. Description DigiKey Part #
IC 1 3 LM556 Dual timer LM556CNFS-ND
Q1 3 2N3906 2N3906FS-ND
D1, 2, 3, 4, 5, 6, 7 21 1N4148 Diode 1N4148FS-ND
R1, 2, 3, 6 12 10K OHM 1/4W Resistor 10KQBK
R3 3 100K OHM 1/4W Resistor 100KQBK
R4 3 33K OHM 1/4W Resistor 33KQBK
R5 5 820 OHM 1/4W Resistor 820QBK
R7 3 330 OHM 1/4W Resistor 330QBK
R8 3 2.2K OHM 1/4W Resistor 2.2KQBK-ND
R9 3 3.3K OHM 1/4W Resistor 3.3KQBK-ND
C1 3 CAP FILM 0.1UF 63VDC RADIAL 495-2465-ND
C2 3 1.0uF 50V Miniature Aluminum Electrolytic 493-1099-ND
TB 2 2 Position Terminal Block - 3.5mm ED2635-ND
TB 1 3 Position Terminal Block - 3.5mm ED2636-ND

Normal Or Advance Green Parts Placement Diagram


Parts For 3 - Normal Green Only Block Circuits

Part Qty. Description DigiKey Part #
IC 1 3 LM556 Dual timer LM556CNFS-ND
D1, 2, 3, 4 12 1N4148 Diode 1N4148FS-ND
R1, 2, 3, 6 12 10K OHM 1/4W Resistor 10KQBK
R3 3 100K OHM 1/4W Resistor 100KQBK
R4 3 33K OHM 1/4W Resistor 33KQBK
R5 5 820 OHM 1/4W Resistor 820QBK
C1 3 CAP FILM 0.1UF 63VDC RADIAL 495-2465-ND
C2 3 1.0uF 50V Miniature Aluminum Electrolytic 493-1099-ND
TB 2 2 Position Terminal Block - 3.5mm ED2635-ND
TB 1 3 Position Terminal Block - 3.5mm ED2636-ND

Normal Only Green Parts Placement Diagram



Using Diodes At The Occupancy Detector Inputs

For More Complex Signaling Systems

  The next diagram shows diodes being used at the BOD inputs to allow 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 STOP by the dispatcher or interlocking until the crossing is clear.

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



Searchlight Signal LED Testing Circuit Schematic

  This circuit can be used to determine the values for R3 and R4 that will produce the best YELLOW indication for a given LED. The circuit lets the user customize the circuit to their preference for the YELLOW indication before constructing a set of signal drivers.

  A variable resistor can be used for R4 to find the best value.

  For more information on the timer used for this circuit see second circuit on this diagram and the 555 Timer web page.


Searchlight Signal Circuit Board Testing



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.

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28 June, 2017