Digital Sensor Breakout Board Assembly Guide

Table of contents

Digital Sensor Breakout Board Assembly Guide

Introduction

The Digital Sensor Breakout Board is a versatile accessory for the LCC Fusion Node Card, designed to provide up to six general-purpose digital connections. Each I/O line can be configured in firmware as either a digital input or a digital output, making the board suitable for a wide variety of layout control and sensing applications.

For inputs, the board supports sensors and devices such as capacitive touch modules, Hall effect switches, mechanical pushbuttons, and other logic-level devices. For outputs, it can drive panel LEDs, relay triggers, or signal lines for external logic devices.

Each I/O line is available through a 3-pin header labeled V (3.3 V), S (Signal), and G (Ground). The signal line connects directly to a GPIO on the Node Card, and includes a built-in 1 kΩ series resistor for added protection. This keeps the design simple and robust while allowing safe connection of a wide range of 3.3 V-compatible devices.

The board connects to the Node Card using a standard RJ45 cable, with six GPIO lines and power shared across the connection. It requires no additional interface or hub, making it ideal for compact, distributed applications. For more complex systems, additional Digital Sensor capabilities can be added using I²C-based expansion cards via the Node Bus Hub.

With its flexible I/O support and simple plug-and-play wiring, the Digital Sensor Breakout Board is an essential building block for interactive and responsive model railroad layouts.

flowchart TD; 
subgraph layout ["Train Layout"];
  direction LR;
  can["CAN Network"];
  can2["CAN Network"];
  sensor1(("Touch Sensor (6x)"));
  output1(("LED Output (6)"));
  nodecard[[Node Card]]; 
  nodecard2[[Node Card]]; 
  card[["Sensor Card"]];
  card2[["Sensor Card"]];
  rsbb["Digital Sensor<br>Breakout Board"];
  rsbb2["Digital Sensor<br>Breakout Board"];

  sensor1 -->|"Voltage (high/low)"|rsbb;
  rsbb -->|"Voltage (high/low)"| card;
  card --> |"GPIO (high/low)"|nodecard;
  nodecard -->|"LCC Event <br/>Touched (yes/no)"| can;

  can2 --> |"LCC Event <br/>Touched (yes/no)"|nodecard2;
  nodecard2 --> |"GPIO (high/low)"|card2;
  card2 -->|"Voltage (high/low)"|rsbb2;
  rsbb2 -->|"Voltage (high/low)"|output1;
end;
classDef lSalmonStyle fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:20px;
class rsbb,rsbb2 lSalmonStyle;
classDef lightGrayStyle fill:#d3d3d3,stroke:#333,stroke-width:2px,font-size:24px;
class layout lightGrayStyle;

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	Purpose	Orientation
Capacitors
C1	1	Ceramic Capacitor	10uF	1206 SMD	Filters high-frequency noise from input to 3V3 voltage regulator	None
C2	1	Ceramic Capacitor	22uF	1206 SMD	Filters high-frequency noise from 3V3 voltage regulator output	None
Connectors
J1-J6	6	JST XH Socket or 2-Position Spring Terminal Connector	2P, 2.54mm	PTH, vertical or horizontal	Connectors to sensors
J7	1	RJ45 Socket	8P8C	PTH	Network cable (CAT5/6) connection from Node Card
Resistors
R1-R6	6	Resistor	100kΩ	1206 SMD	Sets the op-amp gain for sensor resistances from ~1 kΩ to 1 MΩ, producing a 0–3.3 V output suitable for ESP32 ADC input.
Regulator
VR1	1	Voltage Regulator	LM1117-3V3 IC	SMD	3.3 V regulator for Sensors
Sensors
Potentiometer	0-6	n/a	0 Ω–100 kΩ	n/a¹	controller. e.g. user selection detected to set room light level
LDR	0-6	CDS Photoresistor	0 Ω–100 kΩ	n/a²	measure light. e.g. whether room lights are on/off
FSR	0-6	Passive, resistive	0-200g	Thin File Pressure Sensor³	Force detection. e.g. determine whether car is present, or is loaded. User touched panel.

Potentiometer example; RV24YN20S shaft, 0-100kΩ
Photoresistor example; GL5528 (Light ~10–20 kΩ, Dark >500 kΩ)
FSR (Force Sensitive Resistor) example; 0-200g Thin Film Pressure Sensor Flexible Force Sensitive Resistance-type Sensor

Tools Required

List of recommended tools.

Safety Precautions

See Safety Precautions.

Designator (value)	Component	Required?	Orientation
R1-R6	100kΩ, 1206 SMD	Required (one per sensor)	None
U1	LM358 Op Amp	Required (one per sensor)	IC dimple/dot position to PCB top edge
J1-J6	JST XH Socket, Terminal Connector	Required (one per sensor)	Position connection outward
J7	RJ45 Socket	Required	Fits only one way

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.
Use an Digital Multimeter (DMM) to test for continuity between:
- RJ45 socket pin 1 and each sensor V pin
- RJ45 socket pin 2 and each sensor G pin
- RJ45 socket pins 3-8 and each sensor S pin

Functional Testing

Troubleshooting

See I2C Trouble Shooting.

Appendences

Specifications

Specifications for the Resistive Sensor Breakout Board include:

Characteristic	Value
Max Sensors (per breakout board)	6
Max Breakout Boards (per Node Card)	1
Digital Input	3V3
Digital Output	3V3
Dimension	50mm x 72mm

How It Works

The Digital Sensor Breakout Board connects directly to the LCC Fusion Node Card and provides six general-purpose Digital Sensor lines. It supports both digital inputs (such as sensors, switches, or buttons) and digital outputs (such as indicator LEDs, relays, or logic triggers), making it a flexible solution for layout interaction and automation.

Direct GPIO Connection

Each of the six I/O lines is connected through a 3-pin header labeled:

V (3.3 V power)
S (Signal)
G (Ground)

The S pin of each header is connected directly to one of the Node Card’s GPIOs. These GPIOs are fully configurable in firmware as either inputs or outputs, depending on the application.

Input Mode

When configured as an input, the I/O line can accept logic-level signals from external devices such as:

Capacitive touch sensors
Hall effect sensors
Mechanical switches
Digital IR sensors

The firmware provides options for:

Enabling internal pull-ups
Setting debounce timing
Detecting rising, falling, or both edges
Triggering LCC Events when a state change is detected

Each input line includes a built-in 1 kΩ series resistor for protection against shorts or voltage mismatch, ensuring safe connection even in mixed-use environments.

Output Mode

When configured as an output, the Node firmware can drive the I/O lines to:

Light up panel LEDs or route indicators
Activate low-power relays or MOSFET gates
Send logic signals to other modules or control devices

GPIO output states can be controlled directly by:

Node-local logic (such as turnout or signal states)
Incoming LCC Events from the CAN network

This allows the board to participate in coordinated actions across the layout, whether locally triggered or remotely controlled.

Simple Integration and Expansion

The board connects to the Node Card through a single RJ45 cable, carrying:

GND and 3.3 V power
Six signal lines (GPIOs)

It requires no hub or I²C interface and is ideal for direct plug-in applications where small, distributed control or sensing is needed. For larger-scale Digital Sensor needs, additional I²C-based boards can be added via the Node Bus Hub.

Connections

The purpose of the Resistive Sensor Breakout Board and its connectors is to facilitate quick and easy connections between the Node Card and resistive sensors.

Component Designator	Connector Label	Connector Type	Connection Number	Description
J1 - J6	SENSORS 1-6	3-pin JST XH, Spring Terminal	S, V, G	Signal, 3.3V, and GND connections to each sensor
J7	NODE CARD	RJ45 Socket	3v3, GND, S, S, S, S, S, S	Power and sensor connection with Node Card I/O connector (RJ45 socket)