Button Card Assembly Guide

Table of contents

1. Button Card Assembly Guide
   1. Introduction
   2. Assembly and Component Placement
   3. Tools Required
   4. Safety Precautions
   5. Testing and Verification
      1. Visual Inspection
      2. Connectivity Testing
      3. Power-Up Tests
      4. Functional Testing
         1. I2C Verification
         2. Line Verification
   6. Troubleshooting
   7. Appendences
      1. Specifications
      2. How It Works
      3. Protection
      4. References

Introduction

See the How to Use Assembly Guides for detailed instructions.

In conjunction with the LCC Fusion Node Card and a Node Bus Hub, the Button Card provides input control for up to 16 separate buttons. Typically when used for input in an LCC Node arrangement, this card can be attached to input buttons to have the an LCC Node produce LCC Events of on/off. These events are subsequently consumed by a LCC Node to accurately control the functioning states of the other output devices.

flowchart LR; 
can["CAN Network"];
subgraph layout ["Train Layout"];
direction LR;
b["Button Device (16x)"] --> |"Button Press<br/>(on/off)"| bb[I/O Breakout Board];
bb --> |"Digital Input <br/> (high/low)"| c["Button Card (16x)"];
c -->|"GPIO Output <br/> (high/low)"| n[Node Card];
n -->|"LCC Event<br/>(on/off)"| can;
end;
classDef lSalmonStyle fill:#FFA07A,stroke:#333,stroke-width:2px,font-size:24px;
class c lSalmonStyle;
classDef lightGrayStyle fill:#d3d3d3,stroke:#333,stroke-width:2px,font-size:24px;
class layout lightGrayStyle; 

## Terminology

• Accessory Bus

• Bus

• Cleaning PCB

• Component

• Current Limiting Resistor

• Decoupling Capacitor

• Edge Card Connector

• ESD Protection Diode

• Ferrite Bead

• GPIO Expander

• HW Communications Address

• HW Communications Bus

• I2C (Inter-Integrated Circuit)

• I2C Bus

• input_cards - not defined
• jumper_caps - not defined

• LCC Configuration Tool

• lcc_event_id - not defined

• LCC Event Monitoring Tool

• LCC Fusion Breakout Boards

• LCC Fusion Cards

• lcc_fusion_io_cards - not defined
• lcc_fusion_node_bus - not defined
• lcc_fusion_node_card - not defined

• LCC Fusion Project

• MCP23017

• Network Cable

• Stencil

• TVS Diode

For other terms, please refer to the full Terminology Guide.

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

Below is a list of the PCB components used for this card (see diagram before reference):

Component Identifier	Count	Type	Value	Package	Purpose	Orientation
Capacitors
C1 - C16	16	Capacitor-Ceramic	22nF, 50 V	1206 X7R	Low-Pass Filter to filter out noise and prevent unwanted transient signals	None
C17	1	Capacitor-Ceramic	0.1uF, 50 V	1206 X7R	Decoupling capacitor for IC protection.	None
Diodes
D1	1	ESD Diode	PESD1CAN	SOT-23 SMD	I2C data bus electrostatic discharge (ESD) protection.	Fits only one way
F1	1	Fuse-PTC Polymer	PPTC, 0.2A	1206 SMD	Protects from sustained overcurrent conditions	None
Filters & Noise Suppression
FB1, FB2	2	Ferrite Bead	BLM31PG121SN1L	1206 SMD	I2C network bus data line noise suppression.	None
Connectors
J1, J2	2	RJ45 Socket	8P8C	N/A	Network cable (CAT5/6) connection to I/O breakout board connected to buttons.	Fits only one way
Resistors
R1 - R16	16	Resistor	1kΩ	1206 SMD	Current limiting for LED1 - LED16	None
R17-R32	16	Resistor	4.7kΩ	1206 SMD	Low-Pass Filter to filter out noise and prevent unwanted transient signals	None
R38 - R41	4	Resistor	10kΩ	1206 SMD	Used by switch SW1 to pullup the MCP23017 for I2C address.	None
Selectors & Indicators
JP1, JP2	2	Male Header	3P, 0.1” spacing	N/A	Used for LINE 8 and LINE 16 selection of either GND or INPUT. Set to GND when button require this card to provide the circuit’s GND connection.	None
JP3, JP4	2	Male Header	3P, 0.1” spacing	N/A	Used for COMM BUS selection (I2C hardware bus) for either A or B. Must match the configuration within the LCC Node (CDI).	None
SW1	1	DIP / Slide Switch	3P, 2.54mm	N/A	Used for COMM ADDR selection (I2C address offset, 0-7). Up to 8 cards can be installed per I2C bus. Must match the LCC Node configuration (CDI).	Position ON towards PCB top edge
SH1 - SH4	4	Jumper Caps	2.54mm	N/A	Used with I2C Bus and LINE 8/16 selections. Recommend tall caps for ease of use.	None
LED1-LED16	16	LED	Red	1206 SMD	Indicates button has been pressed
ICs
U1, U2, U3	3	IC (Schmitt Trigger)	SN74HCT14	DIP-14 PTH	Contains 6 triggers to transform noisy or slow-changing input signals into clean, fast digital outputs.	Position IC’s dimple (pin 1) towards PCB left edge
U4	1	IC (GPIO expander)	MCP23017	SSOP28	I/O expander using I2C serial interface to control 16 GPIO pins.	Position IC’s dimple (pin 1) towards PCB left edge

Tools Required

List of recommended tools.

Safety Precautions

• See Safety Precautions.

Testing and Verification

Configure the card:

1. Select the I2C bus (COMM BUS) by positioning (2) Jumper Caps on either BUS A or BUS B male header pins (JP1, JP2)
2. Select the I2C address (COMM ADDR) switch (SW1) by slide each of the 3 switches to either the ON or OFF position. Setting a switch to ON increments the address by 1, 2, or 4 for an address range of 0 to 7. Up to 8 devices can then be configured for BUS A and 8 for BUS B.

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.

3. Component Orientation: the IC’s are correctly oriented according to the PCB silkscreen or schematic.

Connectivity Testing

Power-Up Tests

1. Assembly a tested Power Module to the LCC Fusion Node Card.
2. Apply Power to the Power Module and verify the following:
   • Check for Hot Components: Feel for components that are overheating, which could indicate a problem like a short circuit or incorrect component.

Functional Testing

I2C Verification

Line Verification

After validating the LCC Fusion Node Card can connect with the I/O Card, test each of the I/O lines as follows:

1. Connect an network cable (CAT5/6) to RJ45 connector. Use the other end of the cable with a breakout board, or exposed wires to connect to devices for testing.
2. Configure each line of the card for output using an LCC CDI Configuration Tool

Troubleshooting

• See I2C Trouble Shooting.

Appendences

Specifications

Specifications for the card include:

Characteristic	Value
Max Buttons	16
Maximum Number of Cards per LCC Fusion Node Cluster	161

1. The LCC Fusion Node Cluster can support up to 16 cards, distributed across two I2C hardware buses, with a maximum of 8 cards per bus.
   • Note: total includes all cards using the I2C address range of 0x20 (MCP23017 IC).
2. GND, 5V, 12 V (optional), SLA0/SDA0, and SDA1/SCL1 (optional)

How It Works

The Button Card provides up to 16 independent button inputs via a single MCP23017 I²C port expander. Each input line is wired through a clean-up buffer and uses internal pull-ups to detect individual button presses.

1. I2C & MCP23017 Initialization
   • On power-up, the Node Firmware configures the MCP23017 over I2C. Address pins determine the expander’s I²C address.
   • All 16 GPIO pins (GP0–GP15) are set as inputs with internal 3.3 V pull-ups enabled.
2. Button Inputs (Lines 1–16)
   • Each of the 16 MCP23017 inputs connects to a corresponding pushbutton on the RJ45/ribbon header via a Schmitt-trigger buffer (e.g., 74HC14) for clean signal edges and contact bounce suppression.
   • When a button is pressed, its line is pulled LOW to GND; the MCP23017 reads a LOW and triggers a corresponding LCC Event for that button ON.
   • When the button is released, the line returns HIGH via the pull-up, and firmware generates an LCC Event for button OFF.
3. LED Indicators (Optional)
   • For visual feedback, each button line can drive an LED: wire the LED anode to 3.3 V, the cathode through a 1 kΩ resistor to the Schmitt‑trigger output (pre-expander).
   • When the button closes, the buffer output pulls LOW, lighting the LED until the button is released.
4. Debounce & Filtering
   • Purpose: The filter prevents false triggering from mechanical bounce (rapid on/off flicker when a button is pressed or released) and filters out high-frequency noise.
   • How it works: When a button is pressed or released, the contact may momentarily vibrate or bounce, producing a noisy signal. The RC network—composed of a 10 kΩ series resistor and a 10 nF capacitor to ground—slows down these fast voltage changes. This forms a low-pass filter with a time constant (τ) of 0.1 ms, which smooths out spurious transitions.
   • The SN74HCT14 Schmitt-trigger buffer further sharpens the resulting signal by introducing hysteresis, ensuring only clean HIGH or LOW levels are passed to the MCP23017.

LCC Node Operation:

1. The firmware configures the MCP23017 port expander with internal pull-up resistors (set to 3.3 V). When an input device (such as a switch) pulls an input line to LOW (GND), the corresponding GPIO line of the port expander is pulled to LOW.
2. When the LCC Node firmware detects a GPIO state change to LOW, it generates an LCC Event to indicate the ON state. When the input device resets (e.g., the button is released), the GPIO line returns to HIGH, and the firmware generates an LCC Event for the OFF state.

Protection

The Button Card provides detection of button presses. The following is an overview of each protection component integrated into the Button Card and its role:

Protected Component	Protection Component	Function	Specifications	Location
Entire Card	PPTC Polyfuse	Protects from sustained overcurrent conditions by increasing resistance when the current exceeds 1.5A and 3A. Resets once the fault condition is cleared.	Hold Current: 500 mA	In series with the incoming Power line
MCP23017 IC	Decoupling Capacitors	Filters out high-frequency noise and transient voltage spikes from the power supply, ensuring stable voltage to MCP23017 IC.	Values: 0.1 µF ceramic	Across Vcc and GND near IC.
I2C Lines	Ferrite Bead BLM31PG121SN1L	Provides high-frequency noise suppression on the I2C lines.	Impedance: 120 ohms at 100 MHz	In series with the SDA and SCL lines of the I2C bus
I2C Lines	ESD Protection Diode PESD1CAN	Protects the I2C lines from electrostatic discharge and voltage spikes.	Reverse Stand-off Voltage (Vr): 24 VClamping Voltage (Vc): 40 V	Across the SDA and SCL lines to GND
Button Lines	RC Filter + Schmitt Buffer	Reduces EMI, contact bounce, and long-wire interference	Value: 22nF, 4.7kΩ	Inline series resistor, with cap between input line and GND

References

1. Choosing the Right Resistor for LEDs.

2. I2C GPIO Mapping (Button Card)

   RJ45 Line	MCP23017 Pin	GPIO Line	Direction	Pull-up	Logic Levels	Purpose	Notes
   L1	GPA0	GP0	Input	Enabled	LOW = Pressed	Button state reading	Detects LOW when button pressed
   L2	GPA1	GP1	Input	Enabled	LOW = Pressed	Button state reading
   L3	GPA2	GP2	Input	Enabled	LOW = Pressed	Button state reading
   L4	GPA3	GP3	Input	Enabled	LOW = Pressed	Button state reading
   L5	GPA4	GP4	Input	Enabled	LOW = Pressed	Button state reading
   L6	GPA5	GP5	Input	Enabled	LOW = Pressed	Button state reading
   L7	GPA6	GP6	Input	Enabled	LOW = Pressed	Button state reading
   L8	GPA7	GP7	Input	Enabled	LOW = Pressed	Button state reading	May be used for GND detection