Relay Breakout Board Assembly Guide

Table of contents
  1. Relay Breakout Board Assembly Guide
    1. Introduction
    2. Assembly-Configuration Options
    3. Assembly and Component Placement
    4. Safety Precautions
    5. Testing and Verification
      1. Visual Inspection
      2. Functional Testing
    6. Troubleshooting
    7. Appendences
      1. Specifications
      2. How It Works
      3. Connections
      4. Protection
      5. References

Introduction

The Relay Breakout Board is designed to work seamlessly with the Output Card and Node Card, providing reliable control of 5 V devices such as motors, lights, or other accessories that require up to 1A of current. This breakout board uses high-quality relays to switch power to connected devices, ensuring safe and efficient operation for various automation and control applications.

The board contains four relays, each capable of controlling two independent outputs, giving you a total of eight outputs. Each relay is rated for up to 1A of current, making it ideal for controlling low-power devices while providing isolation between the control circuit and the devices being powered.

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  direction LR
  can[CAN Network];
  subgraph hub ["Node Bus Hub"];
    n[["Node Card"]]; 
    c[["Output Card"]];
	end;
  bb1[[Relay<br>Breakout Board]];
  bb2[[Relay<br>Breakout Board]];
  can --> |"LCC Event (On/Off)"|n;
  n -.-> |"GPIO (High/Low)"|c;
  c --> |Output Line High/Low|bb1;
  bb1 -.-> |"Current (on/off)"|d1(("Devices (4x)"));
  bb1 --> bb2;
  bb2 -.-> |"Current (on/off)"|d2(("Devices (4x)"));
end;
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class bb1,bb2 lSalmonStyle;
classDef lightGrayStyle fill:#d3d3d3,stroke:#333,stroke-width:2px,font-size:24px;
class layout lightGrayStyle; 

% include terminology.html %}

Assembly-Configuration Options

The Relay Breakout Board supports multiple assembly configurations to fit various use cases.

Configuration Required/Optional Description Required Components Optional Components
Output Card Required Connection to Output Card for setting relay(s) on off • Turnout Card RJ45 Connector (J6)  
Power via PWR BUS Required Allows board to be powered from layout accessory bus (AC, DC, or DCC) • Connector (J5)
• Bridge Rectifier (BR1)
• 5V Regulator (VR1)
• Filter Capacitors (C1, C2, C3)
• Fuse (F5)
TVS Diode (D5)
Output Devices Optional For controlling each output device • Relay (K1-K4)
• Relay Coils Flyback Diode(D1-D4)
• Fuse (F1-F4)
• Resistors (R1/R2, R3/R4, R5/R6, R7/R8)
• Transistors (Q1-Q4)
• Device Connectors (J1-J4)
—
**2nd Relay Board ** Optional For daisy chaining to a 2nd Relay Board for Output Card lines 5-8 • RJ45 Connector (J7) —

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:

Print PCB Relay Breakout Board PCB
Print
Component Identifier Count Type Value Package Required Purpose Orientation
Capacitors              
C1, C3, C5, C7 4 Capacitor-Ceramic 47uF, 50 V 1206 X7R Required Used for surge buffering of relay coils None
C2, C4, C6, C8 1 Capacitor-Ceramic 0.1uF, 50 V 1206 X7R Required Used for high freq snubbing of relay coils None
C9 1 Capacitor-Polymer Solid 100 ÂľF, 35 V 6.3x5.8mm SMD Required Used by 5V voltage regulator for input filtering. Anode positioned toward PCB top edge
C10 1 Capacitor-Ceramic 0.33 uF, 50 V 1206 X7R Required Used by 5V voltage regulator for input filtering. None
C11 1 Capacitor-Ceramic 0.1uF, 50 V 1206 X7R Required Used by 5V voltage regulator for output filtering. None
C12 1 Capacitor-Ceramic 22 uF, 50 V 1206 SMD Required Used by 5V voltage regulator for output filtering. None
Diodes              
D1 - D4 4 Diode-Schottky SS310 SMA Required for each output Protects against flyback from relay coil Position cathode end (white line) to PCB bottom edge
D5 1 TVS Diode SMAJ5A SMA Optional GPIO pin Transient Voltage Spike (TVS) protection Position cathode end (white line) to PCB top edge
Fuses & Protection              
F1 - F4 4 Fuse-PTC Polymer 1A, >5 V 1206 SMD Required for each relay (pair of outputs) Protects from sustained overcurrent conditions None
F5 1 Fuse-PTC Polymer 1.5A, >5 V JK30, PTH Required Protects from sustained overcurrent conditions None
Connectors              
J1 - J4 4 JST XH Socket or 2-Position Spring Terminal Connector 2P, 2.54mm PTH, vertical or horizontal Required for each output Connector to devices Position connection outward
J5 1 JST XH Socket or 2-Position Spring Terminal Connector 2P, 2.54mm PTH, vertical or horizontal Required Connectors to layout power bus. Position connection outward
J6 1 RJ45 Socket 8P8C PTH Required Connector to Output Card Fits only one way
J7 1 RJ45 Socket 8P8C PTH Optional Connect for daisy chaining a 2nd Relay Breakout Board Fits only one way
Resistors              
R1, R3, R5, R7 4 Resistor 10k Ί 1206 SMD Required for each output device Pullup for transistor gate None
R2, R4, R6, R8 4 Resistor 100 Ί 1206 SMD Required for each output device Current limiting for transistor gate None
Relays & Transistors              
K1 - K4 4 DPDT, TQ2-5 V 1A DIP-10, PTH Required for each output device Controls current to output devices Position IC’s small dimple in corner (pin 1) towards PCB top edge
Q1 - Q4 4 NPN Transistor BSS138 SOT-23, SMD Required for each output device Sets relay on/off Fits only one way
Voltage Regulators              
VR1 1 Voltage Regulator LM7805CV TO-220, SMD Required Provides 5V to output device thru relay Position heat sink towards PCB top edge

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

Troubleshooting

Appendences

Specifications

Specifications for the Relay Breakout Board include:

Characteristic Value
Max Output Devices 4
Max Breakout Boards Per Output Card 4
Output 5 V @ 1A

How It Works

The Relay Breakout Board uses a TQ2‑5V non‑latching (stable) relay, one per channel, to switch each device’s ground in response to a 5 V logic signal from the Output Card.

Device Control (per Channel)

  1. Control Signal & MOSFET Driver
    • Output Line n from the Output Card → 100 Ί gate resistor → BSS138 N‑MOSFET gate.
    • When Output Line n goes HIGH (5 V), the BSS138 turns on and completes the path from the relay coil– pin to ground. This energizes the single coil (coil+ is tied to +5 V), closing the relay contact.
    • When Output Line n goes LOW (0 V), the BSS138 turns off, the coil de‑energizes, and the relay contact returns to its normally‑open state.
  2. Contact Switching
    • Each relay has one set of contacts:
      • COM → connected to the device’s COM (ground) pin
      • NO → connected to the common ground plane
      • NC → unused in this design
    • Coil energize (Output HIGH) → COM–NO closes → device COM tied to GND → device ON
    • Coil de‑energize (Output LOW) → COM–NO opens → device COM floats → device OFF
  3. Common Power Rails
    • A single +5 V rail (from the LM7805CV) feeds:
      • All relay coil+ pins
      • All device V+ inputs
    • Ground is shared across the board; each device’s ground return is switched through its relay.

Independent Channel Operation

  • Each of the four channels is identical:
    • Output Line n drives MOSFET n → energizes Relay n coil → switches Device n COM to ground.
    • Channels operate completely independently—energizing one relay does not affect the others.

Typical Usage Example

  1. Turn Device 1 ON
    • Set Output Line 1 to HIGH → MOSFET 1 conducts → Relay 1 coil energized → COM₁–NO₁ closes → Device 1 COM grounded → device powers.
  2. Turn Device 1 OFF
    • Set Output Line 1 to LOW → MOSFET 1 off → Relay 1 coil de‑energizes → COM₁–NO₁ opens → Device 1 COM floats → device shuts off.
  3. Operate Channels 2–4
    • Repeat the same process on Output Lines 2–4 for Devices 2–4 independently.

Connections

The purpose of the Relay Breakout Board and its connectors is to facilitate quick and easy connections between the Output Card and the output devices.

Component Designator Connector Label Connector Type Connection Number Description
J1 - J4  DEVICE 1-4 JST XH, Spring Terminal V+, COM Connection to output devices
J5 PWR BUS JST XH, Spring Terminal AC/DC/DCC Connection to layout power, regulated to 5V for controlling output devices
J6 OUTPUT CARD RJ45 Socket 1 - 4 Connects Output Card lines 1-4 to a device thru a relay. When 5V present, the relay is close and current flow thru the device.
J7 RELAY BOARD RJ45 Socket 1-4 Connects Output Card lines 5-8 to a daisy chained 2nd Relay Breakout Board which then controls 4 additional devices.

Protection

The Relay Breakout Board includes layered protection to guard against over‑current, inductive spikes, reverse transients and regulator instability. Below is the updated protection summary for your current design.

Protected Element Protection Function Specifications Location
Board Input (5 V supply in) JK30 1.5 A polyfuse Limits sustained over‑current, auto‑resettable Hold: 1.5 A, Trip: ~3–4 A, PPTC Between MB6F bridge output and LM7805 VIN
5 V Bus (after regulation) TVS diode (D5, SMAJ5A) Clamps high‑voltage transients on the 5 V rail 5 V standoff, ~6.4 V breakdown, ~8 V clamp, SMA package Across 5 V → GND right at the LM7805 VOUT pins
LM7805CV regulator Decoupling caps Ensures loop stability, filters high‑frequency noise 0.33 µF ceramic on VIN, 0.1 µF ceramic on VOUT, 100 µF bulk As close as possible to VIN–GND and VOUT–GND pins on the regulator
Each Relay Coil Flyback diode (D1–D4, SS310) Absorbs inductive kick when coil de‑energizes Schottky, 3 A IF, 100 V VR, Vf ≈0.5 V Across each coil: cathode to coil+, anode to coil– (BSS138 drain)
Individual Device Power Lines Slow‑blow fuses (F1–F4) Protects each device from sustained over‑current 1 A slow‑blow (device‑dependent) In series with each device’s V+ input (J1–J4)

Notes:

  • The fast‑blow fuse at the board input stops large faults before they stress the regulator or copper.
  • TVS D5 protects the entire 5 V net from external spikes and surges.
  • Local flybacks (SS310) on each relay coil keep inductive energy out of the shared 5 V bus.
  • Per‑device slow‑blow fuses isolate faults to individual loads, avoiding a full board shutdown on a single device failure.
  • Proper capacitor placement at the LM7805 pins prevents oscillation and keeps your 5 V rail rock‑solid under load.

References


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