PCB Design Guidelines
Table of contents
Table of contents
- PCB Design Guidelines
- Introduction
- PCB Checklist
- Component Placement
- Via Size
- Trace Width Guidelines by Load Type
- Protection
- Filtering for IC Input/Output and Inductive Loads
- 🔧 Hardware ID Voltage Signature Table (3.3 V Divider)
- Signal Integrity
- Power Delivery
- Thermal Considerations
- Component Placement
- Mechanical Design
- Connectivity and Interfaces
- Manufacturability
- Protection and Safety
- Reliability
- Testing and Diagnostics
- Recent Learnings and Iterative Improvements
- Design Iteration and Documentation
- Advanced Power and Signal Considerations
- Improved Connectivity and Modularity
- Enhanced Testing and Troubleshooting
- Future Directions
- Conclusion
Introduction
This document outlines key guidelines and practices adopted in the PCB design process, with a focus on protecting circuit elements from electrical faults and transients. It is also intended to serve as a hands-on learning tool for electronics design, capturing both technical details and reflections on iterative improvements.
PCB Checklist
- PCB layout
- Cards: use Card image (contains correct board outline, copyrights, labels, drill holes)
- Breakout Boards: 50mm height with copyright image on back of board
- PCB naming: on back xxx CARD, xxx BREAKOUT BOARD vx.x
- Component identifiers / values; unique, all labels, labeled top-to-bottom, left–to-right, orientated for reading in one direction
- Component placement:
- filters near IC’s and coil contacts, connectors near edges, etc.
- components at least 1.5mm from edge (PCB housing clearance)
- Component protection: see table below
- Traces: based on usage, see table below
- Connector Labels: identify target /w specifics (i.e. Block, VDC+, COM)
Component Placement
Breakout boards are intended to fit within a UM50 Profile PCB housing. This requires the height of the board to be 50mm. The PCBs slide into the housing, requiring components to be at least 1.5mm from the PCB edge. Below are the offsets by component type:
| Component | Offset (mm) |
|---|---|
| Resistors, Diodes, Capacitors (1206 SMD) | 1.5mm (to pad) |
| Spring Terminal (2.54mm) | 8 (to pin) |
| RJ45 Socket (8p8c, vert) | 8 (to hole center) |
| RJ45 Socket (8p8c, horz) | 9 (to hole center) |
| DIN Rail Screw Spacing | 25.5 (center to center) |
Via Size
Per JLCPCB, the minimal hole size is 0.3mm with ring of 0.1mm. Anything smaller costs extra.
Trace Width Guidelines by Load Type
These recommendations help standardize trace widths across your PCB designs based on the current load type, not specific voltages or components. This table is especially useful when working with LM regulators, filter caps, signal lines, and power buses.
General Recommendations
- ✅ All values assume 1 oz copper thickness (standard for most PCBs).
- ⚡ Voltage is not a factor in determining trace width — current and thermal considerations are key.
- 📏 Shorter traces can safely use thinner widths; longer traces or higher power paths should be wider to reduce voltage drop and heat buildup.
- 🔥 Wider is better when space allows — increased width lowers resistance and improves thermal performance.
- 🛠️ For high-current paths, consider multiple parallel traces or filled copper pours.
- 🧯 Always match ground return traces to the source trace width — don’t bottleneck your return paths.
| Load Type | Max Current (mA) | Recommended Trace Width (mil) |
|---|---|---|
| Sense / Signal Lines | <10 mA | 6 mil |
| Logic-Level GPIO / Control | <20 mA | 6–8 mil |
| I2C / UART / SPI Lines | <50 mA | 8 mil |
| Regulator Filter Caps (Input) | <100 mA | 6–8 mil |
| Regulator Filter Caps (Output) | 250–500 mA | 12–24 mil |
| Low-Power Regulator Output | 250–350 mA | 12–16 mil |
| Medium-Power Regulator Output | 500–750 mA | 24–32 mil |
| High-Power Load (Motors, Wi-Fi) | 750–1500 mA | 32–54 mil |
| Track Bus Power (DCC or DC) | up to 3000 mA | 54+ mil |
| Power Input (to Regulator) | Matches load | Match output path |
| Ground Return Paths | Matches source | Equal to or wider than source |
Protection
| Component | VIN Filtering | Series Filter | Protection |
|---|---|---|---|
| Generic IC | • 0.1 µF Ceramic (50 VDC, 1206 X7R) • 10 µF polymer (50 VDC, 1206 X7R) |
• Ferrite bead (PESD1CAN) | N/A |
| CAN Data Lines (Node Card, Quad-Node Card) | N/A | • Edge damping of reflections before CAN transceiver pins (47Ω) | • Ferrite bead (PESD1CAN) • TVS diodes ( SMBJ18 1206) |
| I2C Data Lines (Node Card, Node Bus Hub, Node Bus Repeater) | N/A | • Edge damping of reflections (47Ω) before ESP32 I2C pins | • Ferrite bead (PESD1CAN) • TVS diodes ( SMBJ18 1206) • Pullups (2.7K) |
| External Power Inputs | • 0.1 µF (50 VDC, 1206 X7R) • 47 µF (50 VDC, 1206 X7R) |
• Ferrite bead (PESD1CAN) | • SMBJ18A TVS (1206) |
| DC Power Input Line Reverse Polarity | • Resettable PolyFuse | • Crowbar Diode | |
| Power Lines | • Resettable PolyFuse • Fast Blow Fuse • Low Voltage Detection |
||
| I/O Lines (Digital/Analog) | • 1K current limiting resistors |
Filtering for IC Input/Output and Inductive Loads
This section outlines key guidelines and practices adopted in the PCB design, with an added focus on protecting circuit elements from electrical faults and transients.
Signal Integrity
Our PCB strictly handles digital signals, ensuring that interference between signal paths is minimized. Signal traces are routed to prevent crosstalk and preserve timing integrity.
Power Delivery
- Stable Supply: Decoupling capacitors are strategically placed adjacent to IC power pins to filter high-frequency noise and maintain voltage stability.
- Input Power Protection:
- Reverse Polarity Protection: Use diodes (e.g., SS310) or MOSFET-based reverse-voltage protection circuits to prevent damage from incorrect power connections.
- Transient Suppression: TVS diodes (e.g., PESD1CAN) and ferrite beads (e.g., BLM21) protect power lines from voltage spikes and EMI.
Notes:
- Caps ≤ 5 mm from device pins
- Route VDC+ & GND side‑by‑side, ≥ 24 mil wide
- Minimize loop area
- VIN Caps
- 0.1 µF ceramic: shunts high-frequency noise on the regulator’s input to ground, preventing oscillations and interference.
- Bulk cap (e.g. 47 µF–100 µF): supplies energy during input-voltage dips or sudden load draws, keeping the regulator’s VIN pin at a steady level.
- VOUT Caps
- 0.1 µF ceramic: provides the fast-edge decoupling needed for regulator stability and to filter high-frequency noise on the output.
- Bulk cap (e.g. 22 µF–100 µF polymer or X7R): acts as a local energy reservoir to handle sudden load changes, maintaining the regulated voltage during transient currents.
- Inductive-Load Decoupling
- 0.1 µF ceramic: placed right across a coil or motor feed to catch very fast voltage spikes when the inductive load switches.
- Bulk cap (e.g. 47 µF X7R): provides the extra current needed by coils or motors during their pull-in time, preventing the supply voltage from dipping.
- Schottky flyback diode: clamps the inductive kick-back voltage when the coil or motor is de-energized, protecting driver transistors and caps.
| Component | VIN Caps | VOUT Caps | Inductive‑Load Decoupling |
|---|---|---|---|
| IC | • 0.1 µF Ceramic (50 VDC, 1206 X7R) «br/>• 10 µF Ceramic (50 VDC, 1206 X7R) • 10k Resistor (1206) |
• N/A | • N/A |
| Power Lines | • TVS Diode (SMBJ18A, 1206) | • N/A | • N/A |
| LM1117‑3.3 Regulator | • 0.1 µF Ceramic (50 VDC, 1206 X7R) «br>• 47 µF Ceramic (50 VDC, 1206 X7R) | • 0.1 µF Ceramic (1206 X7R) • 100 µF polymer (16 V) |
N/A – powers only IC/LED loads |
| LM78xx Regulator | • 0.33 µF Ceramic (50 VDC, 1206 X7R) • 100 µF Polymer (35 VDC) |
• 0.1 µF Ceramic (50 VDC, 1206 X7R) • 22 µF Ceramic (50 VDC, 1206 X7R, 25 VDC) |
• 0.1 µF Ceramic (50 VDC, 1206 XR7) • 47 µF Ceramic (50 VDC, 1206 XR7) at each coil/motor feed |
| LM2596S‑ADJ Regulator | • 0.1 µF Ceramic (50 VDC, 1206 X7R) • 100 µF Polymer (35 VDC) |
• 0.1 µF Ceramic (50 VDC, 1206 X7R) • 100 µF Polymer (35 VDC) |
• 0.1 µF Ceramic (50 VDC, 1206 XR7) • 47 µF Ceramic (50 VDC, 1206 XR7) at each coil/motor feed |
| M54562FP Stepper Driver | • 0.1 µF Ceramic (50 VDC, 1206 X7R) right at VCC pin • 100 µF polymer (35 VDC) on VCC if space allows |
• N/A | • N/A (External flyback diodes connected to motor contacts provide additional protection, supplementing the internal diodes of the driver for handling flyback current from inductive loads). |
| TB6612FNG Motor Driver | • 0.1 µF Ceramic (50 VDC, 1206 X7R) <right at VCC (pin 20) • 47 µF Ceramic (50 VDC, 1206 X7R) on VM1 (pin 24) and VM2 (pin 13), if space allows |
• N/A | N/A (internal MOSFET body-diodes handle flyback; external Schottky diodes across each motor winding are still recommended for extra protection) |
| TQ2 Relay | • N/A | • N/A | Across relay coils: • 0.1 µF Ceramic (50 VDC, 1206 XR7) • 47 µF Ceramic (50 VDC, 1206 XR7) • Schottky flyback diodes |
You’re welcome! Here’s the updated Markdown-formatted version of the Hardware ID Voltage Signature Table, including the additional future card entries, all based on a 3.3 V reference (with R1 fixed at 10 kΩ):
🔧 Hardware ID Voltage Signature Table (3.3 V Divider)
R1 is fixed at 10 kΩ (connected to 3.3 V) R2 is unique per card (connected to GND) Voltage is calculated as: Vout=3.3 × (R2 / (R1+R2))
See HwIdCheck.h for implementation.
| Card Name | R1 (kΩ) | R2 (kΩ) | Voltage (V) | Firmware Range (V) |
|---|---|---|---|---|
| Node Card | 10 | 5.6 | 2.12 | 2.00 – 2.25 |
| DCC Card | 10 | 4.7 | 2.24 | 2.10 – 2.35 |
| Sound Card | 10 | 2.7 | 2.58 | 2.45 – 2.70 |
| Audio Card | 10 | 1.8 | 2.77 | 2.65 – 2.90 |
| UOD Card | 10 | 10 | 1.65 | 1.50 – 1.75 |
| (Future) Card F1 | 10 | 1.0 | 3.00 | 2.85 – 3.15 |
| (Future) Card F2 | 10 | 0.68 | 3.15 | 3.00 – 3.30 |
| (Future) Card F3 | 10 | 0.47 | 3.24 | 3.15 – 3.35 |
⚠️ Notes
- All voltages are based on a 3.3 V system reference.
- ESP32 ADC inputs are not 5 V tolerant — using a 5 V divider could damage the pin.
- These ranges include ±5% margin to allow for resistor and ADC tolerances.
- Voltages above ~3.3 V are avoided to stay within ESP32 ADC safe operating limits.
Signal Integrity
Our PCB strictly handles digital signals, ensuring that interference between signal paths is minimized. Signal traces are routed to prevent crosstalk and preserve timing integrity.
Power Delivery
-
Stable Supply:
Decoupling capacitors are strategically placed adjacent to IC power pins to filter high-frequency noise and maintain voltage stability. - Input Power Protection:
- Reverse Polarity: Incorporate protection devices (e.g., Schottky diodes, MOSFET-based circuits) to guard against accidental reverse polarity.
- Reverse Current: Implement circuits (such as resettable polyfuses or directional diodes) that prevent harmful reverse current flow.
- Output Power Protection:
- Include reverse current protection measures on output lines to safeguard connected devices from backflow currents.
Thermal Considerations
Components are selected to minimize heat generation, with overall current draw kept below 3A. Voltage regulators feature integrated heat sinks, ensuring safe operating temperatures without extensive thermal management.
Component Placement
- Identification & Orientation:
- PCB silk screening clearly labels components for easy identification. Labels are uniformly oriented and sequenced from the upper left, following a logical layout.
- Similar components are grouped and aligned, facilitating straightforward assembly and troubleshooting.
- Accessibility:
- Components are chosen to support both manual DIY assembly and automated reflow soldering.
- SMD parts are optimized for solder paste application and stencil alignment, with tooling holes included for precision.
Mechanical Design
PCBs are engineered for simple assembly. Standardized component sizes (e.g., 1206 SMD resistors and capacitors) and mounting provisions (e.g., board holes for DIN adapters, screws, or casings) ensure versatile installation options.
Connectivity and Interfaces
- Inter-Board Communication:
- Cards connect seamlessly with the Node Bus Hub via card edge connectors, supported by standoffs and an ‘orientation key’ to enforce correct alignment.
- Robust 8-wire network cables link Cards and Breakout Boards.
- External Connections:
- Connector placements near PCB edges offer flexibility for external wiring, with various socket options available (e.g., ATX connectors for larger gauges, JST XH for smaller wires).
Manufacturability
- Designed and tested with industry-standard tools (such as Fritzing), ensuring compatibility with various PCB design platforms.
- 2-layer board designs facilitate modifications, while provided Gerber files support economical production (e.g., via JLCPCB).
- Use of common, readily available components aids both DIY enthusiasts and professional assembly services.
Protection and Safety
To safeguard circuit integrity and prolong board life, the following protection measures are integrated throughout the design:
- IC Protection
- Current Limiting & Filtering: Deploy current-limiting resistors and filtering capacitors at IC power inputs to stabilize voltages and suppress transient disturbances.
- I2C Interface Protection
- Automated Termination & Pull-Up Integration: Automated design ensures the proper placement and sizing of pull-up resistors for I2C lines.
- Noise Filtering & Transient Protection: Filtering components and ESD/TVS diodes shield against electrical transients.
- CAN Bus Protection
- 120-Ohm Termination Automation: Automated design steps ensure that 120-ohm termination resistors are correctly applied to maintain differential signal integrity.
- Filtering, ESD, and TVS: Supplement CAN lines with noise filters and protective components (ESD diodes, TVS devices) to defend against interference and voltage spikes.
- Overall Communications Protection
- Both I2C and CAN lines are further reinforced with dedicated noise filtering, ESD safeguards, and TVS circuits, ensuring reliable data transmission under adverse conditions.
Reliability
- ESD & EMI Protection
- ESD protection diodes (e.g., PESD1CAN) are placed on communication lines.
- Ferrite beads (e.g., BLM31PG121SN1L) are used to suppress high-frequency noise.
- Ease of Maintenance
- The board layout supports simple replacement, with quick-connect terminals and modular design elements.
- The Node Card design includes female headers for easy swapping of modules, with configuration backup tools (via JMRI) facilitating seamless transitions.
Testing and Diagnostics
- The Node Bus Hub streamlines wiring and configuration during testing phases.
- Functional checks use designated cards and breakout boards equipped with buttons and LEDs.
- Serial monitor capabilities and event-driven testing (via JMRI tools) support comprehensive connectivity and I/O diagnostics.
Recent Learnings and Iterative Improvements
As our project evolves, the following enhancements based on recent work have been integrated into the design guidelines:
Design Iteration and Documentation
-
Iterative Feedback Loop:
Each design phase now includes a brief retrospective. This record captures the decisions made, challenges encountered, and the outcomes of performance tests. Incorporating these learnings helps refine subsequent iterations and supports reproducibility. -
Documentation as a Learning Tool:
Updated documentation includes real-world application examples and troubleshooting guides. Reflections on challenges—such as unexpected noise issues or layout constraints—are shared to benefit both current and future design efforts.
Advanced Power and Signal Considerations
-
Enhanced Decoupling Strategies:
Our recent prototypes have shown that introducing additional decoupling on sensitive nodes improves overall signal stability. This revision outlines more aggressive capacitor placement strategies where needed. -
Dynamic Signal Routing:
Testing revealed that subtle adjustments in trace layouts further mitigate crosstalk. Updated guidelines now emphasize flexible routing practices that consider real-time signal integrity measurements.
Improved Connectivity and Modularity
-
Modular Interface Improvements:
Based on user feedback, the design now includes clearer guidelines for inter-board connectivity. Detailed notes on orientation keys and standardized connector placements ensure that both assembly and maintenance are streamlined. -
Interchangeable Components:
Emphasis has been placed on modularity. By grouping similar circuits and standardizing interface modules, future design revisions can be more readily integrated or replaced without affecting overall system performance.
Enhanced Testing and Troubleshooting
-
Automated Diagnostics:
Recent experiences have led to a greater reliance on serial monitoring and event-driven testing approaches. The integration of automated diagnostics tools into the testing phase has improved reliability and expedited fault isolation. -
Guided Test Procedures:
New test routines are documented in detail. These include step-by-step procedures and typical test outcomes, making the testing phase both a learning opportunity and a robust quality check.
Future Directions
-
Versioned Changelogs:
Moving forward, each major iteration of the board will include a versioned changelog embedded in this documentation. This log will detail key changes, lessons learned, and future recommendations. -
Community and Collaborative Enhancements:
As this documentation is shared on GitHub, community contributions and feedback will further refine these guidelines. A section dedicated to user contributions and FAQs will be maintained to ensure continuous improvement.
Conclusion
This document now not only covers essential design guidelines for PCB development but also integrates our ongoing learnings and iterative improvements. By blending technical standards with reflective insights, we aim to create a dynamic resource that evolves with the project, supporting both effective design and continuous learning.