Subjects: Assembly Guides , Automation , Hardware , Signaling
Use Cases: Automation Deployment , Node Cluster Setup , PCB Design & Assembly , Signaling Systems , Train Detection
Relay Breakout Board Assembly Guide
Table of contents
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.
flowchart LR;
subgraph layout ["Train Layout"];
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;
classDef lSalmonStyle fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:24px;
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) |
â |
**2nd Relay Board ** | Optional | For daisy chaining to a 2nd Relay Board for Output Card lines 5-8 | ⢠RJ45 Connector (J7) | â |
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:
- PCB for the card can be ordered from any PCB fabricator using these Gerber Files.
- Clean PCB with alcohol to remove residue. See Cleaning_PCB for details.
- See also: Soldering Tips
- PCB Components - listing of components used for PCB assembly
- PCB Parts - listing of parts used for PCB assembly
Component Identifier | Count | Type | Value | Package | Required | Purpose | Orientation |
---|---|---|---|---|---|---|---|
Capacitors | Â | Â | Â | Â | Â | Â | Â |
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 | Â | Â | Â | Â | Â | Â | Â |
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 | Â | Â | Â | Â | Â | Â | Â |
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 | Â | Â | Â | Â | Â | Â | Â |
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 | Â | Â | Â | Â | Â | Â | Â |
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 ICâs 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 | Â | Â | Â | Â | Â | Â | Â |
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
- See Safety Precautions.
Testing and Verification
Visual Inspection
- Initial Check: Examine the board for any obvious issues like missing components, solder bridges, or components that are misaligned or not fully seated.
- 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
- See I2C Trouble Shooting.
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 TQ2â5V nonâlatching (stable) relay, one per channel, to switch each deviceâs ground in response to a 5 V logic signal from the Output Card.
Device Control (per Channel)
- Control Signal & MOSFET Driver
- Output Line n from the Output Card â 100 Ί gate resistor â BSS138 NâMOSFET gate.
- When Output Line n goes HIGH (5 V), the BSS138 turns on and completes the path from the relay coilâ 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 deâenergizes, and the relay contact returns to its normallyâopen state.
- Contact Switching
- Each relay has one set of contacts:
- COM â connected to the deviceâs COM (ground) pin
- NO â connected to the common ground plane
- NC â unused in this design
- Coil energize (Output HIGH) â COMâNO closes â device COM tied to GND â device ON
- Coil deâenergize (Output LOW) â COMâNO opens â device COM floats â device OFF
- Each relay has one set of contacts:
- 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 deviceâs ground return is switched through its relay.
- A single +5 V rail (from the LM7805CV) feeds:
Independent Channel Operation
- Each of the four channels is identical:
- Output Line n drives MOSFET n â energizes Relay n coil â switches Device n COM to ground.
- Channels operate completely independentlyâenergizing one relay does not affect the others.
Typical Usage Example
- Turn Device 1 ON
- Set Output Line 1 to HIGH â MOSFET 1 conducts â Relay 1 coil energized â COMââNOâ closes â Device 1 COM grounded â device powers.
- Turn Device 1 OFF
- Set Output Line 1 to LOW â MOSFET 1 off â Relay 1 coil deâenergizes â COMââNOâ opens â Device 1 COM floats â device shuts off.
- Operate Channels 2â4
- Repeat the same process on Output Lines 2â4 for Devices 2â4 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 - J4Â | 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 overâcurrent, 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) | JK30âŻ1.5âŻA polyfuse | Limits sustained overâcurrent, autoâresettable | Hold: 1.5âŻA, Trip: ~3â4âŻA, PPTC | Between MB6F bridge output and LM7805 VIN |
5 V Bus (after regulation) | TVS diode (D5, SMAJ5A) | Clamps highâvoltage transients on the 5 V rail | 5 V standoff, ~6.4 V breakdown, ~8 V clamp, SMA package | Across 5 V â GND right at the LM7805 VOUT pins |
LM7805CV regulator | Decoupling caps | Ensures loop stability, filters highâfrequency noise | 0.33 ÂľF ceramic on VIN, 0.1 ÂľF ceramic on VOUT, 100 ÂľF bulk | As close as possible to VINâGND and VOUTâGND pins on the regulator |
Each Relay Coil | Flyback diode (D1âD4, SS310) | Absorbs inductive kick when coil deâenergizes | Schottky, 3 A IF, 100 V VR, Vf â0.5 V | Across each coil: cathode to coil+, anode to coilâ (BSS138 drain) |
Individual Device Power Lines | Slowâblow fuses (F1âF4) | Protects each device from sustained overâcurrent | 1 A slowâblow (deviceâdependent) | In series with each deviceâs V+ input (J1âJ4) |
Notes:
- The fastâblow 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.
- Perâdevice slowâblow 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 rockâsolid under load.