Turnout Coil Switch Machine Breakout Board Assembly Guide

Table of contents
  1. Turnout Coil Switch Machine Breakout Board Assembly Guide
    1. Introduction
      1. Application Design Diagram
      2. Usage
    2. Assembly and Component Placement
    3. Tools Required
    4. Safety Precautions
    5. Testing and Verification
      1. Visual Inspection
      2. Functional Testing
    6. Troubleshooting
    7. Appendices
      1. Specifications
      2. How It Works
      3. Protection
      4. Connections
      5. References

Introduction

The Turnout Coil Switch Machine Breakout Board, used in conjunction with the LCC LCC Fusion Node Card, Turnout Card, and a coil switch machine, provides both motor control and turnout point position sensing, while also handling frog polarity switching. The board leverages a set of transistors to reliably switch the frog connection between Rail A and Rail B, based on the turnout’s position, ensuring proper electrical connection as the turnout moves between the Thrown and Closed positions.

By interfacing directly with the Turnout Card, this breakout board provides a seamless way to control the turnout motor direction and manage frog polarity automatically, making it ideal for complex layout control and automation.

This board contains a Capacitor Discharge Unit (CDU) to drive the coil switch machines using solenoid coils to move the points. The CDU can be charged directly from the Turnout Card. Connection to the PWR BUS is optional.

Application Design Diagram 

flowchart LR; 
can["CAN Network"];
subgraph layout ["Train Layout"];
n["Node Card"]; 
nb["Node Bus Hub"];
c["Turnout Card"];
bb[Turnout Coil <br/> Switch Machine <br/> Breakout Board];
frog1["Frog 1"];
frog2["Frog 2"];
direction LR;
smotor1["Single-Coil, or<br/>Twin-Coils"];
smotor2["Single-Coil, or<br/>Twin-Coils"];

onodes["Other LCC Nodes"] <-->  |"Event ID"| can;
can <-->  |"Event ID"| n;
subgraph cluster ["LCC Fusion Node Cluster"];
n <---> |"GPIO Signal <br/> (high/low)"| nb;
nb <--> |"Commuications <br/>Power"| c;
end;
c <--> |"Turnout Control <br/> (12 V, direction, status)"| bb;

bb --> |"DC Power <br/>(150 ms on / off)"| smotor1;
bb --> |"Track Power <br> (Rail A/B)"| frog1;
bb --> |"DC Power <br/>(150 ms on / off)"| smotor2;
bb --> |"Track Power <br> (Rail A/B)"| frog2;
pbus["PWR BUS"] --> |"AC/DC/DCC"|bb;
tbus["TRACK BUS"] --> |"AC/DC/DCC"| bb;
end;
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class layout lightGrayStyle;

Usage

This breakout board is for use with both 2-wire switch machines using one solenoid (single coil) and 3-wire switch machines using two solenoids (twin-coils).

Manufacturer Product Switch Machine Type Breakout Board to Switch Machine Connects Frog Polarity Points Status1 Comments
KATO Unitrack Turnout Single-Coil Connect 1 to red wire
Connect 2 to black wire		 Breakout Board Breakout Board Configure Turnout Card for 12 V DC Motor Output
Rapido Rapido RailCrew Switch Machine Single-Coil Connect 1 to red wire
Connect 2 to black wire		 Breakout Board Breakout Board Configure Turnout Card for 12 V DC Motor Output
Atlas Snap Switch Machines Twin-Coils Connect 1 to left connector
Connect COM to middle connector
Connect 2 to right connector		 Breakout Board Breakout Board  
Hornby R8014 Point Motor
R8243 Surface Mount Point Motor		 Twin-Coils Connect 1 to Red wire
Connect COM to Black wire
Connect 2 to Green wire		 Breakout Board Breakout Board Configure Turnout Card for12 V DC Motor Output.
R8014 Wiring (PDF)
R8243 Wring (PDF)
Model Railroad Control Systems (MRCS) MP1, MP1 (v2), MP5 Twin-Coils Connect 1 to poz1 connector
Connect COM to COM connector
Connect 2 to poz2 connector		 Breakout Board, or
MRCS MP1, MP5		 Breakout Board MP1 Wiring (PDF)
MP5 Wiring (PDF)
For MP4 & MP10, use Turnout Slow Motion Switch Machine Breakout Board
Peco TwistLock Motor (PL-1000, PL-1000E
Turnout Motor PL-10/PL-10E
Pico Side Mount		 Twin-Coils Connect 1 to Black or Red wire
Connect COM to both Green wires
Connect 2 to other Black or Red wire		 Breakout Board, or
Peco Turnout Motor (PL10)		 Breakout Board PL10 Wiring (PDF)
Switch 1 and 2 connections to reverse motor
Rails Connect (by DCCconcepts) Rails Connect Point Motors RPM-SM.1, RPM-UB.1 Twin-Coils Connect 1 to Red wire
Connect COM to Green wire
Connect 2 to Black wire		 Breakout Board Breakout Board  
  1. To produce LCC Events, the breakout board is must be used since the switch machine itself is not integrated with LCC.
## Terminology

For other terms, please refer to the full Terminology Guide.

Assembly and Component Placement

This section combines both the component specifications and the assembly instructions to ensure a smooth assembly process. Below is a comprehensive list of components, their placement on the PCB, and orientation details to assist you during assembly.

High-Level Steps for Assembly:

Component Identifier Count Type Value Package Purpose Orientation
Capacitors            
C1 1 Capacitor-Polymer 100 uF, 35 V 6.3x5.8mm SMD Smooths rectified DC voltage See silk screen image
C2 1 Capacitor-Ceramic 0.33 uF, 50 V 1206 X7R Smooth input for voltage regulator None
C3 1 Capacitor-Ceramic 22 uF, 50 V 1206 X7R Smooth output for voltage regulator None
C4 1 Capacitor-Ceramic 0.1 uF, 50 V 1206 X7R Smooth output of voltage regulator None
C5, C6 2 Aluminum Capacitor 2200 uF, 25 V 13mm Provides current to drive coil switch coils Position anode towards PCB right edge
C7, C16 2 Capacitor-Ceramic 10 uF, 50 V 1206 X7R Part of the 150 ms pulse timing circuit (RC) to control discharge rate None
C8, C11, C12, C15 4 Capacitor-Ceramic 47uF, 50 V 1206 X7R Use to handle bulk energy for the relay coil’s inrush None
C9, C10, C13, C14 4 Capacitor-Ceramic 0.1uF, 50 V 1206 X7R Use of relay coil high-frequency snubbing None
Diodes            
BR1, BR2 2 Bridge Rectifier MB6F SMD Converts DCC/AC to DC Position indent to PCB left edge (pin1 DC-)
D1 1 TVS Diode SMAJ5A SMA GPIO pin Transient Voltage Spike (TVS) protection Cathode end has a white line and positioned towards PCB top edge
D2, D4, D7, D9 4 Diode SS310 SMD Flyback for relay coils Cathode end has a white line and positioned towards PCB left edge
D3, D10 2 Diode SS310 SMD A negative-clamp, preventing the PWM input from swinging more than 0.6 V below GND and thus ensuring clean, well-defined PWM edges Cathode end has a white line and positioned towards PCB left edge
D5, D6, D19, D20 4 Diode SS310 SMD Reverse current protection for RC circuit Cathode end has a white line and positioned towards PCB left edge
D8, D9 2 Diode SS210 SMD Reverse current protection from motor driver output to relay coil (-) Cathode end has a white line and positioned towards PCB left edge
D11-D18 8 Diode SS310 SMD Flyback for switch machine coils Cathode end has a white line and positioned towards PCB left edge
Fuses & Protection            
F1, F2 2 Fuse-PTC Polymer JK30, 1.5A, 16 V (or more) 5.1mm, PTH Current overload protection from track (frog) None
Connectors            
J1 1 JST XH Socket 2P, 2.54mm PTH or Spring Terminal Connector to PWR BUS (V+, GND) for charging 2200uF capacitor and regulator for TB6612FNG IC motor driver Position connection towards PCB top edge
J2 1 JST XH Socket 2P, 2.54mm PTH or Spring Terminal Connector to turnout frog Position connection towards PCB top edge
J3 1 JST XH Socket 2P, 2.54mm PTH or Spring Terminal Connector to track bus  power rails (Rail A and Rail B)  
J4, J5 2 JST XH Socket 2P, 2.54mm PTH or Spring Terminal Connector to switch machines (coils) Position connection towards PCB top edge
J6 1 RJ45 Socket 8P8C PTH Network cable (CAT5/6) connection from I/O Card Fits only one way
Resistors            
R1 1 Resistor 68Ω 1206 SMD Limits current to capacitor for 1 sec charge time None
R2, R3, R10, R11 4 Resistor 10kΩ 1206 SMD Pullups for Optocoupler LED Anode None
R4, R7 2 Resistor 15kΩ 1206 SMD Part of the 150 ms pulse timing circuit (RC) to control discharge rate None
R5, R6, R8, R9 2 Resistor 1kΩ 1206 SMD current limiting to Optocoupler LED Anode None
ICs            
U1, U2 2 Optocoupler MCT6H DIP8, PTH Convert RJ45 bipolar control signal into lower power signals to Motor Drivers (U1, U2) Position IC’s indent towards PCB top edge
U3 1 Motor Driver TB6612FNG SSOP-24 Drives coil(s) with pulse bipolar Position IC’s dimple/dot towards PCB top/right edges
Voltage Regulators            
VR1 1 Voltage Regulator LM7805CV TO-220, SMD Provides 5V to relays, 2200uF, optocoupler, and Drive Motor (U1, U2) Position heat sink towards PCB top edge
RELAY            
K1, K2 2 Relay DPDT TQ2-L2-12V TQ2, DIP-10 Switches Track A/B to Frogs Indent (black line) towards PCB top edge

Tools Required

List of recommended tools.

Safety Precautions

Testing and Verification

Visual Inspection

  1. Initial Check: Examine the board for any obvious issues like missing components, solder bridges, or components that are misaligned or not fully seated.
  2. Solder Joint Inspection: Use a magnifying glass or a microscope to inspect solder joints. Look for cold solder joints, insufficient or excessive solder, or any shorts between pads.

Functional Testing

  1. Connect accessory bus to PWR BUS connector (J1)

  2. Connect track bus rails to TRACK BUS connector (J3)

  3. Test Motor 1

    1. Connect a single or twin coil switch machine to MOTOR 1 (J4)

    2. Momentarily connect 12 V+ (e.g. accessory bus) to RJ45 socket (J5) pin 1 and GND to pin 2.

      Access RJ45 pins from PCB bottom). Pin 1 has a square solder pad. Pin 2 is position above it, with other pins alternating between the rows.

    3. Results:

      • one of the motor’s coils moves the turnout points in one direction.

  4. Check for movement by the 2nd turnout coil by momentarily touching 12 V+ to pin 2 and GND to pin 1.

Troubleshooting

Appendices

Specifications

Specifications for the Turnout Coil Motion Switch Machine Breakout Board include:

Characteristic Value
Input (Layout’s power bus or dedicated supply) 12 V–35 V AC, DC, or DCC
Max Coil Switch Machines (per Breakout Board) 2
Max Coil Switch Machines (per LCC Node Cluster) 8 (per 1 sec of charging)1
Max Input Current (CDU charging) 12 V @ 180 mA for 1 sec
Max Output (to each Coil) Up to 25 V @ 150 ms per 2200 µF2,4
Max Output (Track Bus to Frog) 2.5 A3

  1. The default 12 V used for 1-second CDU charging is supplied via the Turnout Card. The LCC Node Cluster provides 12 V @ 1.5A, supporting up to 8 breakout boards charging simultaneously. Optionally, the user may offload this power by connecting an external power supply or layout-wide power bus (PWR BUS).

  2. Coil resistance varies by manufacturer. Some switch machines may not operate reliably with a single 2200 µF capacitor. If this occurs, install the jumper (JP1) to connect a second 2200 µF capacitor, effectively doubling the pulse energy.

  3. Output current to the frog from the Track Bus is limited by the PCB trace width of 48 mil (typically supports ~2.5 A with 1 oz copper).

  4. If the switch machine stalls or the throw is insufficient, consider increasing the capacitor value in the RC timing circuit (keep all four capacitors the same value).

    Pulse Time (τ = R × C) Resistors (R10,R11,R14,R15) Capacitors (C6-C9)
    150 ms (0.15s) 15kΩ 10uF
    30 ms (0.3s) 15kΩ 22uF
    500 ms (0.5s) 15kΩ 33uF

How It Works

The Turnout - Coil Switch Machine Breakout Board is designed to control both single-coil and twin-coil switch machines using a flexible, pulse-based drive system. It integrates seamlessly with the LCC system via the Turnout Card, supports AC, DC, or DCC input, and uses a motor driver IC to manage turnout movement. The board also includes configurable energy output and sensing support for turnout position feedback, with frog polarity now handled by a TQ2-L2 dual-coil latching relay.

Power Supply and Conditioning:

  • The primary source of power is the Turnout Card. The bipolar 12 V is rectified using a bridge rectifier to provide a stable DC 12 V supply.
    • Note that the board optionally supports receiving AC, DC, or DCC power through the PWR BUS, which is rectified using a bridge rectifier to provide a stable DC supply. This will override the use of power from the Turnout Card.
  • A 5 V regulator (e.g., LM7805) supplies power to the TB6612FNG motor driver and logic components.
  • A 2200 µF capacitor is charged through a 68 Ω resistor to store energy for driving the turnout coil.
  • A jumper (JP1) allows the user to connect a second 2200 µF capacitor, increasing energy to 4400 µF for larger switch machines.

Input and Direction Control:

  • Directional signals arrive from the Turnout Card via RJ45 Pins 1 and 2 for switch 1 (pins 5/6 for switch 2), carrying polarity-based control for turnout direction.
  • These signals are isolated and converted using a dual optocoupler (MCT6H), producing OC1 and OC2 outputs.
  • Each optocoupler’s output connects to both:
    • The AIN1/AIN2 direction for switch 1 (BIN1/BIN2 for switch 2) inputs of the TB6612FNG motor driver
    • An RC timing circuit (10 µF + 15 kΩ + SS310 diode) that generates a ~150 ms pulse to the PWMA for switch 1 (PWMB for switch 2) input
    • Pullups (10k) when OC1/OC2 are off so they are not floating (TB6612FNG has no internal pullups)

Coil Pulse via Motor Driver:

Note: A TB6612 motor driver instead of discrete MOSFETs because it provides reliable polarity control for dual-coil latching relays in a compact form factor with fewer components.

  • The TB6612FNG receives:
    • Direction from AIN1/AIN2 and BIN1/BIN2 (via the 2 optocouplers)
    • Pulse from RC circuit (to PWMA/PWMB)
    • Motor power from VM1 (connected to the charged capacitor)
  • When triggered, the TB6612FNG outputs a 150 ms burst across AO1 and AO2, delivering power to the turnout coil(s).
  • For twin-coil switch machines, the COM terminal is connected to GND, and the output pulse is applied to Coil 1 or Coil 2 based on direction.

Flyback Protection:

  • Four SS310 Schottky diodes are used across the coil terminals (1/COM and 2/COM) to suppress voltage spikes when the coils deactivate, protecting the motor driver.

Frog Polarity Switching (via TQ2-L2 Relay):

  • The board employs a TQ2-L2 dual-coil latching relay to control the polarity of the frog. One coil is dedicated to setting the relay, while the other is used to reset it.

  • Each relay coil is driven directly by the motor driver’s output using a 150 ms pulse. The two coils are wired in opposite directions, so a change in the motor driver’s output polarity selectively energizes either the set or reset coil.
  • This approach ensures reliable, momentary actuation without requiring continuous power, which could lead to overheating or damage in a latching relay. Since latching relays are designed to hold their state mechanically, continuous current is unnecessary and potentially harmful.
  • The TQ2-L2 relay reliably toggles the frog connection between Track Bus A and Track Bus B, ensuring the frog always matches the polarity of the selected route.

Turnout Point Sensing:

  • The optocoupler outputs (OC1/OC2) also pull the RJ45 sense lines Pins 3/4 for Switch 1 and Pins 7/8 for Switch 2 low depending on direction.
  • This allows the Turnout Card to determine if the switch is in the thrown or closed position.

The board is compatible with both 1-coil and 2-coil switch machines, with no jumper required. Users simply wire their switch machine using 2 or 3 terminals depending on the design. The board is engineered for ease of use, protection, and reliable turnout control using a mix of analog and digital logic.

<img src=”/LccFusionProject/assets/images/pcbs/Breakout_Boards/Turnout_Coil_Switch_Timing.png/” style=”zoom:30%; float:center” /

Timing and Pulse Generation Explanation

The diagram above illustrates how the Turnout - Coil Switch Machine Breakout Board uses a shared RC timing circuit to convert a directional polarity signal (via OC1/OC2) into a brief, high-current pulse for the motor driver input (PWMA). Here’s a breakdown of what’s happening across each transition:

  1. Key Components Involved

    • MCT6H Optocoupler (OC1/OC2):

      • Detects the polarity of the control signal from the Turnout Card.
      • Only one channel is HIGH at any time, based on current flow direction.

      • Acts as both a signal isolator and a logic switch.

      • Series Diodes (D1, D2):
        • One diode is inline between each optocoupler output and the shared RC timing circuit.
        • Prevents back feeding between OC1 and OC2, ensuring isolated triggering.
      • RC Timing Circuit (R + C):
        • A resistor (e.g., 15kΩ) and ceramic capacitor (e.g., 10µF X7R) form a charge circuit.
        • When OCx goes HIGH, the capacitor begins to charge, creating a voltage ramp.
        • This rising voltage is seen at the PWMA pin of the TB6612FNG.
      • PWMA Input (Motor Driver):
        • Recognizes a HIGH signal (typically >2V) to enable the motor channel for a pulse.
        • As the capacitor voltage drops below ~0.8V, PWMA returns LOW.
        • This delivers a single ~150 ms burst to the motor coil, preventing overheating.

    • Discharge Diode (D3):

      • Connected from PWMA to GND (cathode to PWMA).
        • Ensures the capacitor can discharge cleanly after each pulse, resetting the circuit.

  2. Pulse Cycle

    1. Turnout is Thrown (OC1 HIGH):
      • OC1 goes HIGH
      • Capacitor begins charging through R
      • PWMA crosses HIGH threshold → motor pulse starts
      • After ~150 ms, capacitor is fully charged, PWMA falls to LOW causing motor driver to turn off current to turnout coil
    2. Turnout Holds Position:
      • OC1 remains HIGH
      • Capacitor remains charged (no further current flow)
      • PWMA remains LOW (motor driver off)
      • Coil is safe from prolonged current
    3. Turnout is Closed (OC2 HIGH):
      • OC1 goes LOW, OC2 goes HIGH
      • Same process repeats through D → R → C
      • PWMA sees new 150 ms pulse → motor actuates in other direction

âś… Benefits of This Approach

  • No firmware timing required
  • Safe, non-latching control of coil motors
  • Only one pulse per change, regardless of signal duration
  • Universal compatibility with most single- and twin-coil switch machines

Protection

Protected Component Protection Component Function Specifications Location
Turnout Card (MCP23017 GPIOs) MCT6H Optocoupler Electrically isolates control signals from high-current switching, preventing back-EMF and voltage spikes from reaching the Turnout Card. - Isolation Voltage: 5300 V RMS
- Forward Current: 10 mA
- Output Type: Open-Collector		 Between RJ45 input control signals and Relay
5 V Regulator & Power Supply Bridge Rectifier Ensures correct polarity, allowing AC, DC, or DCC power sources while preventing reverse polarity damage. - Maximum Input Voltage: 600 V AC
- Forward Current: 0.5A (Max 1A surge)
- Forward Voltage Drop: 1.1 V per diode
- Reverse Leakage Current: 5µA (at 600 V)		 Between external power input and 5V regulator
Accessory Power (ACC V+) TVS Diode Provides overvoltage protection to prevent damage from voltage spikes on the accessory bus Voltage clamp at specified level (e.g., 12 V) Across the ACC V+ and ACC GND power lines
Track Power PPTC Polyfuse Protects from sustained overcurrent conditions by increasing resistance. Resets once the fault condition is cleared. Fuse Rating: Based on max track current (typically 0.5-3.5A depending on track power). In series with the track power supply, between the power source and the track.
Coil Motors Flyback Diode Protects the circuit from high-voltage spikes caused by inductive loads (switch machine coils) when switching off. Diode Type: Schottky
Max Current: Min 2A
Reverse Voltage: Min 25 V		 Across the turnout switch machine coils.
LM7805CV Regulator Capacitors (Input/Output) Stabilizes voltage and reduces noise on the input and output of the voltage regulator. Input Cap: 470uF, 0.33µF Output Cap: 0.1µF Input cap across the input pin and GND. Output cap across the output pin and GND.
DCC and ACC Circuits Separate Ground Planes Isolates DCC and accessory grounds to prevent interference N/A Between DCC and ACC
         

Connections

The purpose of the Turnout Twin Coils Switch Machine Breakout Board and its connectors is to facilitate quick and easy connections between the Turnout Card and a turnout controlled by twin-coils (i.e. snap switches)

Component Designator **Connector Label ** Connector Type Connection Number Description
J1 PWR BUS JST XH, Spring Terminal 1, 2 AC/DC connection to the layouts accessory bus or dedicated power supply (not to DCC). GND must connected to the same ground plane as the LCC Fusion Node Card.
J2 FROGS JST XH, Spring Terminal 1, 2 Connection to power turnout frogs
J3 TRACK BUS JST XH, Spring Terminal A, B Connections to the layout track bus for Rail A and Rail B. Used to power the frog when. If necessary, switch the connections to match the frog to the correct rail.
J4, J5 MOTOR 1 / MOTOR 2 JST XH, Spring Terminal 1, 2 Connection to 1 or 2 twin-coils switch machines. Connections 1 and 2 are for one side of each coil. COM is for the shared connection of the 2 coils.
J6 TURNOUT CARD RJ45 Socket 1 - 8 Refer to Turnout Card’s connection table for the function of each pin
JP1 COIL BOOST JUMPER n/a Use Jumper Cap to boost power to the coils by using (2) 2200uF capacitors.

References

Last updated on: May 10, 2025 © 2025 Pat Fleming