Relay Breakout Board Installation Guide 

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

Overview

The Relay Breakout Board interfaces with an Output Card, Digital I/O Card, or Node Card to switch up to four 5 VDC devices at currents up to 1 A each. It uses TQ2-L-5V relays driven by MOSFETs for safe isolation between the control logic and the load devices, making it ideal for motors, lights, or other low-power accessories on your layout.

Power is supplied from the layout’s accessory power bus (AC, DC, or DCC), rectified and regulated to 5 VDC on-board. Control signals arrive via an RJ45 connection from the controlling card.

What’s Needed

Component Purpose
Relay Breakout Board Provides relay switching and on-board power regulation
Output Card / Digital I/O Card / Node Card Supplies control signals (lines 1–4)
Network Cable (RJ45) Carries control signals from the card to the relay board
4 × Device Connectors (J1–J4) Connect up to four 5 VDC devices (motors, LEDs, relays, etc.)
3-wire jumper cables or wiring Attach devices to JST-XH or spring-terminal connectors
Accessory Power Bus Provides 5 VDC regulated input (< 40 VDC AC/DC/DCC before on-board regulator)
(Optional) Second Relay Board Daisy-chain control lines 5–8 via RJ45 connector (J7)

Connection Diagram 

flowchart LR
  subgraph Train Layout
    direction LR
    card[["Node Card,<br>DigitialI/O Card, or<br>Ouput Card"]]
    breakout1["Relay <br>Breakout Board"]
    breakout2["2nd Relay <br>Breakout Board"]
    devices1["Controlled Devices (4x)"]
    devices2["Controlled Devices (4x)"]
    pwrbus("PWR BUS <br>(AC/DC/DCC)")
  end
  card <--> |"Network Cable → J10" |breakout1
  breakout1 <--> |"2-wire → J1...J4"|devices2
  breakout1 <--> |"Network Cable → J11" |breakout2
  breakout2 <--> |"2-wire →  J1...J4"|devices1
  pwrbus <--> |"2-wire Cable →  J9"|breakout1

Connector Assignments

Label Connector Function
J1–J4 DEVICE 1–4 5 VDC device switched to ground via relay on control (COM -> NO)
J5 PWR BUS 5 VDC regulated power input from layout accessory bus
J6 CONTROL IN (RJ45) Control lines 1–4 from Output/Digital I/O/Node Card
J7 DAISY CHAIN (RJ45) Control lines 5–8 to second Relay Breakout Board (opt.)

Installation Steps

  1. Mount the board in your enclosure or control panel, allowing access to J1–J7.

  2. Power connection:
    • Connect the layout accessory bus (AC/DC/DCC) to J5.
    • Verify ~5 VDC at the board’s 5 VDC rail with a multimeter.
  3. Control signal:

    • Plug a standard RJ45 network cable between the RJ45 socket (J6) and a Output Card, Digital I/O Card, or Node Card I/O RJ45 socket.

      Note: when using the Node Card I/O socket, set the Node Card LINE 7 selector to I/O, and the LINE 8 selection to I/O

  4. Device wiring:
    • Attach each device to J1–J4 using 2-wire cables:
      • Pin 1 → COM
      • Pin 2 → NO
  5. Optional daisy chain:
    • To control outputs 5–8, connect J7 to J6 of a second Relay Breakout Board.
  6. Activate control lines 1–4 from the host card and confirm each relay clicks and the attached device energizes.

Wiring Suggestions & Best Practices

  • Use 22–18 AWG wiring for device power connections up to 1 A.
  • Keep signal and power wiring separate from high-voltage AC or noisy cables.
  • For motors or inductive loads, add additional suppression (RC snubbers) at the device if necessary.
  • Label all cables and connectors to avoid mix-ups during maintenance.
  • Secure RJ45 and JST connectors to prevent intermittent contact in operation.

Status Indicators

  • Audible Relay Clicks: Each relay emits a soft click when energized.
  • No on-board LEDs: Use a multimeter or indicator LEDs on devices to verify operation.

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 Description Test Points Expected Result
Check for Power LED Visual inspection near VR1 LED is ON
Verify Power at PWR BUS (J5) Multimeter across J5 VDC+ and GND >12 VDC (AC, DC, or DCC layout power supply)
Verify 5 VDC Regulator Output Multimeter across 5 VDC rail (e.g., COM at J1–J4 to board’s GND) ~5.0 VDC
Relay Activation Test Trigger Output Card Line 1–4 and observe relays Audible click for each relay when activated
Device Power Output Multimeter across J1–J4: COM (pin 1) to NO (pin 2) ~5 VDC when relay is ON, 0 VDC when relay is OFF
Daisy-Chain Test (if used) Repeat relay and output tests on second Relay Breakout Board (J6) Same results as above for output lines 5–8 (J5)

🧰 Troubleshooting Flow

The following diagram provides a step-by-step decision flow to help you verify that the board is installed and functioning correctly. It guides you through simple tests that can be performed using basic tools (e.g., multimeter, jumper wire, or Node Monitor), and helps isolate common installation issues such as:

  • Incorrect power or wiring
  • Misconfigured CDI settings
  • Device or connection faults
  • Hardware issues requiring builder attention

Each question in the diagram leads to an action or recommendation. Follow the flow from left to right. If you reach a “Likely Bad Board” node, set the board aside for further bench testing or builder support.

💡 These flows are intended for installers. Builders or testers should refer to the corresponding bench-level troubleshooting flow if needed.

  flowchart TD
  subgraph "Relay Breakout Board Test Flow"
    direction LR
    Connect-Power("Connect supply power to <br>PWR BUS connector (J5)") 
    Connect-Card("Connect <br>Digital I/O Card,<br>Output Card, or<br>Node Card I/O")
    Connect-Device("Connect <br>device to connectors <br>COM, NO (J1–J4)")
    Activate-Device("Activate relay")
    Activate-Input-Line("Bypass card: <br>Apply 5 V to each <br>input line (J6)")
    
    LED-Q{"Is the Power LED ON?"}
    PWR-Q{"Measure voltage <br>at PWR BUS (J9):<br><br>Is voltage >14 V?"}
    Device-On-Q{"Do connected devices <br>turn ON/OFF correctly?"}
    Relay-Click-Q{"Did the relay click<br>when the device was <br>expected to turn ON?"}
    Input-Test-Q{"Does the <br>corresponding <br>device turn ON?"}

    Fix-PWR["Check layout <br>power wiring, <br>power supply <br>voltage"]
    Fix-CDI["Check card, <br>CDI configuration"]
    Fix-Device["Check device wiring, polarity,<br>or replace device"]
    Bad-Board["Likely bad Relay <br>Breakout Board <br><br>Contact builder"]

    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
    
    Device-On-Q -- "Yes, device working" --> Success
    Device-On-Q -- "No, device not working" -->  Relay-Click-Q
    Relay-Click-Q -- "Yes, relay clicked" --> Fix-Device
    Relay-Click-Q -- "No, relay did not <br>click (activate/deactivate)" -->   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:18px;
  classDef error fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:18px;
  classDef success fill:#c6f6c6,stroke:#2c7a2c,stroke-width:2px,font-size:18px;
  classDef action fill:lightblue,stroke:#2c7a2c,stroke-width:2px,font-size:18px;

  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 Start,Success success;

Safety Notes

  • Always disconnect power before making wiring changes.
  • Do not exceed 1 A per line; verify device specifications.
  • Replace fuses only with the specified 1 A slow-blow type (F1–F4).
  • Avoid short circuits between VDC+ and GND on device connectors.

References

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