Digital I/O Card & Breakout Board Installation Guide 

Table of contents
  1. Digital I/O Card & Breakout Board Installation Guide
    1. Overview
    2. What’s Needed
    3. Connection Diagram
    4. Installation Steps
    5. Wiring Suggestions & Best Practices
    6. Status Indicators
    7. Testing & Troubleshooting
    8. Safety Notes
    9. References

Overview

The Digital I/O Breakout Board interfaces the Digital I/O Card with up to eight digital input or output devices. It supports a wide variety of devices such as sensors, buttons, LEDs, and small actuators used in model railroad automation and other low-power control applications.

The board is powered from one of the layout’s power bus (AC, DC, or DCC), rectified via an onboard bridge rectifier, and regulated to a stable 5 VDC supply for the devices and board circuitry.

What’s Needed

Component Purpose
Computer / RPI (3B+)1 Runs JMRI for CAN communications with Node Card
Node Card  & Power Supply Interfaces with CAN network and cards (via Node Bus Hub)
Digital I/O Breakout Board Interfaces digital I/O signals and power for digital I/O devices
Digital I/O Card Interfaces with Node Card via serial communications and converts digital I/O to signals for the Digital I/O Breakout Board.
Digital I/O Devices (8 max) Sensors, buttons, LEDs, relays, or actuators
Network Cable (CAT5/CAT6) Connects Digital I/O Card to Digital I/O Breakout Board via RJ45 connector
3-wire cables Connect devices to breakout board JST XH connectors
Layout Power Bus (AC/DC/DCC) Supplies breakout board power (<40 VDC, AC/DC/DCC)

1) When using an RPi, you can simplify integration by using the RPi-CAN Card, which provides built-in CAN communication and connects directly to the LCC Fusion Node Bus—no extra wiring required. Otherwise, to run JMRI on a standalone Pi you will need:

  • Raspberry Pi 3B+ (or newer): Runs JMRI for CAN communications. We recommend Steve Todd’s preconfigured JMRI image
  • microSD card (8 GB or larger): Holds the JMRI OS image
  • microSD card reader & imaging tool: For flashing the image to your card (e.g., balenaEtcher)

Connection Diagram 

flowchart
  subgraph layout ["Train Layout"]
  	subgraph hub["Node Bus Hub"]
      nodeCard[["Node Card"]]
      ioCard[["Digital I/O Card"]]
    end
    jmri["JMRI Software<br>CDI Config Tool"]
    computer["Computer, or <br>Raspberry PI"]
    pwrSupply(("Power Supply"))
    breakout1["Digital I/O <br>Breakout Board"]
    breakout2["2nd Digital I/O <br>Breakout Board"]
    devices1(("Digital I/O Devices (8x)"))
    devices2(("Digital I/O Devices (8x)"))
    pwrbus(("PWR BUS <br>(AC/DC/DCC)"))
  end
  jmri -.- |"runs on"|computer <--> |"CAN Bus via<br>Network Cable"|nodeCard
  pwrSupply -.-> |"1+ A @ 40 v max via<br>2-wire"| nodeCard
  nodeCard <--> |"Digital I/O via<br>Node Bus"|ioCard
  ioCard <--> |"Digital I/O via<br>Network Cable → J10" |breakout1
  breakout1 <-.-> |"I/O via<br>2-wire → J1...J8"|devices1
  breakout1 <--> |"I/O via<br>Network Cable → J11" |breakout2
  breakout2 <-.-> |"Digital I/O via<br>2-wire →  J1...J8"|devices2
  pwrbus <--> |"14+ VDC via<br>2-wire Cable →  J9"|breakout1

  classDef lightBlueStyle fill:lightblue,stroke:#2c7a2c,stroke-width:2px,font-size:16px;
 	classDef lightGreenStyle fill:lightgreen,stroke:#333,stroke-width:2px,font-size:20px;
  class hub lightBlueStyle
  class ioCard,breakout1,breakout2 lightGreenStyle

Installation Steps

  1. Connect the Digital I/O Breakout Board to the Digital I/O Card using a standard network cable (RJ45).
  2. Connect the layout Accessory Power Bus (AC, DC, or DCC) to the breakout board’s power input (J9).
  3. Connect up to eight digital devices to the breakout board’s 3-pin JST XH connectors:
    • Pin 1: 5 VDC power (from board regulator, used for input device power)
    • Pin 2: Signal line (digital input or output)
    • Pin 3: Ground (common reference)
  4. Configure the Node Card firmware to set each I/O line as input or output as required by your application.
  5. Ensure wiring polarity and connections match device requirements — input devices expect power on Pin 1, output devices receive control signals on Pin 2.

Wiring Suggestions & Best Practices

  • Always connect device ground to Pin 3 (GND) for common reference.

  • For input devices (e.g., sensors, switches), connect device power to Pin 1 (5 VDC) and signal output to Pin 2 (Signal).

  • For output devices (e.g., LEDs, relays), device power is typically shared from the same 5 VDC rail; device control line connects to Pin 2, device ground to Pin 3.

  • Use shielded or twisted pair cables where possible to reduce noise on signal lines.

  • Avoid mixing input and output device connections on the same physical line without proper configuration to prevent damage.

  • Consult device datasheets for power and signal wiring requirements.

  • Ensure firm and secure connections to JST headers and network cables.

    Device Type I/O Type Typical Wires Device Wire for 5V Pin Device Wire for SIG Pin Device Wire for GND Pin Notes
    Digital Sensor (e.g., proximity, IR) Input 3 VDC+ Signal (SIG) GND Sensor powered by 5 VDC; outputs digital signal
    Push Button / Switch Input 2 n/a Yes Yes Configure via CDI as Input with internal pull-up enabled
    LED (ON/OFF control) Output 2 n/a Anode Lead Cathode Lead Configure Digital I/O Card with 1kΩ current limiting resistor
    DC 5V Relay Module Output 3 VDC+ Signal (SIG) GND  
    5V Buzzer Output 2 n/a Yes Yes Simple ON/OFF control

Status Indicators

  • Power LED: Illuminates when 5 VDC power is present and regulated on the breakout board.

Testing & Troubleshooting

  • Cables & Connections
    • Ensure the network cable between the Digital I/O Card and Breakout Board is fully seated and oriented correctly.
    • Verify accessory bus voltage and polarity at the board’s power connector.
    • Confirm device wiring matches the board pinouts (signal, VDC+, GND).
  • Firmware & Diagnostics
    • Use the LCC Configuration Monitor (JMRI), serial console, or other diagnostic tool to check that inputs register and outputs toggle as expected.
Test Check Point Expected
Power LED LED beside VR1 LED is ON
PWR BUS Voltage J9 VDC+ → GND > 12 VDC (AC, DC, or DCC)
5 VDC Regulator J1–J4 VDC+ → GND ≈ 5.0 VDC
Device Activation Output lines 1–4 via J10 Outputs switch on/off; inputs generate LCC Events
Daisy-Chain I/O Lines 5–8 via J11 Same results on lines 5–8

🧰 Troubleshooting Flow

Refer to the Output Device Flow and Input Device Flow diagrams for step-by-step guidance on isolating wiring, power, firmware, and device issues. If you reach a “Likely Bad Board” node, set the board aside for bench testing or builder support.

Output Device Text Flow

  flowchart TD
    subgraph "Output Device Test Flow" 
      direction LR
      Connect-Power("Connect supply power to <br>PWR BUS connector (J5)")   
      Connect-Card("Connect <br>Digital I/O Card")
      Connect-Device("Connect <br>output devices <br>(lamps, LEDs)<br>to connectors <br>(J1–J8)")
      Activate-Device("Activate input <br>device (LCC Event)")
      Activate-Input-Line("Bypass Digital <br>I/O Card: <br>Apply 5 V to each <br>input line (J6)")
      	
      LED-Q{"Is the Power LED ON?"}
      PWR-Q{"Measure input at PWR BUS (J9).<br><br>Is voltage >14 V?"}
      Device-On-Q{"Do connected devices <br>turn ON correctly?"}
      Input-Test-Q{"Does the <br>corresponding <br>device turn ON?"}
      
      Success[["✅ Installation <br>Successful"]]
      
      Connect-Power --> LED-Q
      LED-Q -- "Yes, power LED is On" --> Connect-Card --> Connect-Device --> Activate-Device --> Device-On-Q
      LED-Q -- "No, power LED is Off" --> PWR-Q
      PWR-Q -- "Yes, valid input power" --> Bad-Board
      PWR-Q -- "No, invalid input power" --> Fix-PWR
      
      Fix-PWR["Check layout <br>power wiring, <br>power supply <br>voltage"]
      Fix-CDI["Verify card is good. <br>Check cards's <br>CDI configuration"]
      Fix-Device["Check device <br>wiring, polarity,<br>or replace device"]
      Bad-Board["Likely bad <br>Digital I/O<br>Breakout Board <br><br>Contact builder"]
  
      
      Device-On-Q -- "Yes, device working" --> Success
      Device-On-Q -- "No, device not working" -->   Activate-Input-Line --> Input-Test-Q
      Input-Test-Q -- "Yes, device works without <br>Output Card" --> Fix-CDI
      Input-Test-Q -- "No, device not working" -->  Bad-Board
    end
  
    %% Color styles
    classDef question fill:#d3d3d3,stroke:#333,stroke-width:2px,font-size:16px;
    classDef error fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:16px;
    classDef success fill:#c6f6c6,stroke:#2c7a2c,stroke-width:2px,font-size:16px;
    classDef action fill:lightblue,stroke:#2c7a2c,stroke-width:2px,font-size:16px;
  
    class LED-Q,PWR-Q,Relay-Click-Q,Input-Test-Q,Device-On-Q question;
    class Fix-PWR,Fix-CDI,Fix-Device,Bad-Board error;
    class Connect-Power,Connect-Card,Connect-Device,Activate-Device,Activate-Input-Line action;
    class Success success;

Input Device Test Flow

flowchart TD
  subgraph "Input Device Test Flow"
    direction LR
    Connect-Power("Connect supply power to <br>PWR BUS connector (J5)") 
    Connect-Card("Connect <br>Digital I/O Card")
    Connect-Device("Connect <br>input devices <br>(buttons, sensors)<br>to connectors <br>(J1–J8)")
    Activate-Device("Activate input <br>device")
    
    LED-Q{"Is the Power LED ON?"}
    PWR-Q{"Measure voltage <br>at PWR BUS (J9):<br><br>Is voltage >14 V?"}
    IOCard-Detect-Q{"Is input device detected <br>(CDI Event, <br>Card I/O line low)?"}
    Simulated-Input-Q{"Temporarily short <br>connector pins 1/2 <br>(J1-J8):<br><br>Does the <br>Digital I/O Card <br>detect the <br>input change?"}

    Fix-PWR["Check layout <br>power wiring, <br>power supply <br>voltage"]
    Fix-CDI["Check Digital I/O <br>Card CDI <br>config information"]
    Fix-Device["Bad input device: <br>Check device wiring, <br>polarity, and operation"]
    Bad-Board["Likely bad<br>Digital I/O Breakout Board<br><br>Contact builder"]
    
    Success["✅ Input Device<br>Detection Verified"]
    
    Connect-Power --> LED-Q
    LED-Q -- "Yes, power LED is On" --> Connect-Card --> Connect-Device --> Activate-Device --> IOCard-Detect-Q
    LED-Q -- "No, power LED is Off" --> PWR-Q
    PWR-Q -- "Yes, valid input power" --> Bad-Board
    PWR-Q -- "No, invalid input power" --> Fix-PWR
    
    IOCard-Detect-Q -- "Yes, device detected" --> Success
    IOCard-Detect-Q -- "No, device not detected" --> Simulated-Input-Q
    Simulated-Input-Q -- "Yes, simulated input succesful" --> Fix-Device
    Simulated-Input-Q -- "No, simulated input not detected" --> Fix-CDI
    Fix-CDI --> Bad-Board
  end
    %% Color styles
  classDef question fill:#d3d3d3,stroke:#333,stroke-width:2px,font-size:16px;
  classDef error fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:16px;
  classDef success fill:#c6f6c6,stroke:#2c7a2c,stroke-width:2px,font-size:16px;
  classDef action fill:lightblue,stroke:#2c7a2c,stroke-width:2px,font-size:16px;

  class LED-Q,PWR-Q,Input-Wired-Q,IOCard-Detect-Q,Simulated-Input-Q question;
  class Fix-PWR,Fix-CDI,Fix-Device,Bad-Board error;
  class Connect-Power,Connect-Card,Connect-Device,Activate-Device action;
  class Success success;

Safety Notes

  • Disconnect power before making or changing device connections.
  • Do not exceed device current limits; max current is limited by the 5 VDC regulator and wiring.
  • Use appropriate fusing on the accessory power bus to prevent damage.

References

Last updated on: December 17, 2025 © 2025 Pat Fleming