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Turnout Indication LED Projects

Turnout Position Indication – If you want to save some money by not buying an expensive system here is a suggestion for building your own system which has the following attributes:

(1) Use of Green and Red LEDs on your Main Control Panel to indicate Turnout position, Green straight ahead, Red to the right or left.

(2) Use of only Green LEDs on a separate Yard Panel to depict the turnout train path selected.

(3) For those turnouts that require momentary toggle switches to activate dual coil switch machines, for example ATLAS or PECO a Latching Circuit can be used to memorize the recently activated turnout position.

(4) A series of signal heads placed near each turnout which will track the turnout position selected on the Main or Yard Control Panel. More about Signal Heads in another paragraph.

The one disadvantage to the scheme is that it does not actually give the operator any feedback as to whether or or not the Turnout has been thrown because it only latches the last momentary toggle switch position.

The figure below depicts the overall concept in block diagram form.

Detailed Description of above diagram

The diagram depicts two Power Supplies.

Power Supply #1 is a 12 vdc, 1 amp wall-wart type or equivalent, that is used to energize the twin coil machines (Turnouts). Notice that the two coils are tied together via a jumper wire. Notice that + 12 vdc from PS #1 is hard-wired to both coils. Either coil is energized by the application of the PS#1 Return line via momentarily toggling Switch S1 to either one side or the other. Notice that S1 is a momentary double pole switch mounted on the Control Panel.

Power Supply #2 is a 12 vdc, 1 amp wall-wart type or equivalent, that is used as a power source for the Latch Network. As either coil is energized by the application of the PS#1 Return line via momentarily toggling Switch S1 a SET or RESET Signal is created and routed to the Latching Network. The SET and RESET inputs are normally biased at + 12 vdc from PS# 2. If a SET is selected via S1, then the input to resistor R1 becomes a Logic zero (12 vdc Return) and the RESET input to R2 remains at a Logic one (+12 vdc). If a RESET is selected via S1, then the input to resistor R2 becomes a Logic zero (12 vdc Return) and the SET input to resistor to R1 remains at a Logic one (+12 vdc).

The important thing to remember is that the Output of the Latching Network (Q) will hold or memorize the last state (SET or RESET) that was last toggled to by S1.

Voltage-wise the Output of the Latching Network will either be +12 vdc or zero vdc. If it is +12vdc, then the Green LED on the Control panel will be lit. If it is Zero vdc, then the Red LED will light.

What I have described above is available on one fourth of an Integrated Circuit (Chip). Therefore, one Integrated Circuit such as the CD 4044BC will program four Turnouts. It is possible to fit four of these Integrated Circuits into a Radio Shack Project Enclosure (7 x 5 x 3), giving one the capability to control sixteen turnouts.

The Latching Network can be packaged as part of the Control Panel with or without an enclosure. Remember that an enclosure usually requires connectors that mate to the outside world. The Detailed Schematic Information below reflects an actual design to control 16 turnouts (4 Chips to control 16 Turnouts packaged in a Project Enclosure with the following 37 pin connectors for interface to the Control Panel and the Track Signal Heads.

Connector Data

For Large Project Box:

Quantity = 2; Part Number DUBSCM37; Description 37 Contact Male Solder Cup Connector

Quantity = 2; Part Number DUBSCF37; Description 37 Contact Female Solder Cup Connector

Quantity = 2; Part Number DSUBCH37; Description 37 Pin Connector Hood

Detailed Schematic Information for Chip U1

Four Chips U1 through U4 are used in a large Project Box to control 16 Pecos on my layout. The above Schematic shows the necessary interconnections. Specifically the J1 connector is a 37 pin P/N ? used to interface with the Main Control Panel which contains the LED Turnout Position Indicators attached to the appropriate spot on the pictorial of the track layout which appears on the panel surface. It also interfaces U1 and U2 to the Track Signal Heads on the layout via the Main Front Panel LEDs. There is also another connector J2 which is also part of the Project Box. It interfaces with U3 and U4.

The resistors (Rs) depicted above are all of the same value, 10k, 1/4 watt. Each resistor is wired to some sort of bus terminal within the Project Box. The other ends of the resistors are wired to the associated signal pin on the Chip.

Detailed Schematic Information for Chip U2

In the figure below it can be seen that U2 is wired in a similar fashion to U1, except that it reflects being used with Turnouts 5 through 8.

Detailed Schematic Information for Chip U3

In the figure below it can be seen that U3 is wired in a similar fashion to U1, except that it reflects being used with Turnouts 9 through 12 and it uses connector J2 on the Project Box.

Detailed Schematic Information for Chip U4

In the figure below it can be seen that U3 is wired in a similar fashion to U2, except that it reflects being used with Turnouts 13 through 16 and it uses connector J2 on the Project Box.


Signal Heads

Signal Head wiring is relatively simple in concept. Each Signal Head is generally made up of one green LED and one red LED.  The can be wired in parallel to the corresponding LEDs on the Control Panel. Refer to the figure below  and simply wire the positive side of the Red LED on the Control Panel to the positive side of the RED LED on the Signal Head; likewise wire the negative side of the Green LED on the Control Panel to the negative side on the Signal Head.

In the above figure, resistors R3 and R4 are each about 750 ohms each if the Signal Head LEDs are also used.  This is because we have pairs of diodes in parallel so that the overall circuit draws twice the current. Normally R3 and R4 would would have been 1500 ohms each.

P.S. You can save some money by buying existing Signal Heads and removing the existing light bulbs and replacing them with LEDs.

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

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