CAN BUS sniffer

CANBUS Sniffer PCB

A compact USB-to-CAN Bus interface designed around an STM32F0 microcontroller and a CAN transceiver. This project was built to practice professional PCB design techniques from schematic capture through PCB layout while following industry design practices.

Version: V1.0.0

Features

• USB Type-C Interface
• STM32F0 Microcontroller
• CAN Bus Transceiver
• USB 2.0 Full-Speed Differential Pair
• 3.3V Linear Regulator
• TVS Protection
• Reverse Polarity Protection
• Power LEDs
• CAN Activity LEDs
• SWD Programming Header
• RESET Button
• BOOT Button
• Four Mounting Holes
• Four-Layer PCB

Project Images

PCB Layout with Ground Pours

3D Render with Ground Pours

Schematic

Routed PCB

3D Render

Overview

The goal of this project was to design a complete CAN Bus Sniffer PCB using KiCad while applying professional hardware engineering methodologies.

The board receives power over USB Type-C, regulates the voltage to 3.3V, communicates over a CAN transceiver, and provides an SWD interface for programming and debugging.

Rather than only creating a working PCB, this project focused heavily on layout quality, manufacturability, and signal integrity.

Topics practiced include:

• PCB floorplanning
• Component placement
• USB differential pair routing
• Controlled impedance routing
• Four-layer PCB stackup
• Power distribution
• Ground plane implementation
• Decoupling capacitor placement
• EMI reduction techniques
• Design Rule Checks (DRC)
• Design for Manufacturability (DFM)
• Design for Assembly (DFA)

Hardware Specifications

PCB Stackup

Layer 1

• Components
• Signal Routing
• USB Differential Pair

Layer 2

• Solid Ground Plane

Layer 3

• Solid Ground Plane

Layer 4

• Signal Routing
• Power Routing

Using two dedicated internal ground planes provides:

• Continuous return paths
• Reduced EMI
• Improved signal integrity
• Lower ground impedance
• Better high-frequency performance
• Improved power distribution

Engineering Design Decisions

USB Type-C

USB Type-C was selected for modern compatibility and ease of use.

USB CC pull-down resistors were implemented to correctly identify the board as a USB device.

The USB D+ and D− lines were routed as a differential pair using KiCad's differential pair router.

Special attention was given to:

• Matched trace lengths
• Constant spacing
• Controlled impedance
• Minimal discontinuities
• Smooth routing
• Short path between the connector and downstream circuitry

Differential Pair Routing

Although USB Full-Speed is more forgiving than USB High-Speed, the layout follows professional differential routing practices.

Design considerations included:

• Constant differential spacing
• Matched lengths
• 45° bends
• Minimal skew
• No unnecessary vias
• Short routing distance
• Continuous reference plane underneath the pair

Power Architecture

Power flow:

USB Type-C
    ↓
Protection Circuit
    ↓
Filtering
    ↓
3.3V LDO
    ↓
STM32 + CAN Transceiver

Wide power traces were used where appropriate to reduce voltage drop and improve current handling.

Power Integrity

Each power pin is locally decoupled with ceramic capacitors placed as close as possible to the corresponding IC supply pins.

This reduces:

• Supply noise
• Voltage ripple
• Transient voltage drops
• EMI

Grounding Strategy

The board utilizes:

• Layer 2 Solid Ground Plane
• Layer 3 Solid Ground Plane
• Top Ground Pour
• Bottom Ground Pour
• Ground stitching vias

This creates low-impedance return paths and improves signal integrity throughout the design.

The exposed thermal pad underneath the STM32 is connected directly into the internal ground planes through a thermal via.

CAN Interface

The CAN transceiver converts the MCU CAN peripheral into differential CANH and CANL signals suitable for automotive communication.

The layout emphasizes:

• Short routing
• Clean return paths
• Differential signaling
• Noise immunity

Crystal Oscillator

The crystal and its load capacitors were placed immediately adjacent to the MCU oscillator pins.

This minimizes:

• Loop area
• EMI susceptibility
• Clock jitter

Component Placement

Components were grouped by function:

USB Section

• USB Connector
• ESD Protection
• CC Resistors

Power Section

• Protection
• LDO
• Filtering
• LEDs

CAN Section

• CAN Connector
• CAN Transceiver
• Termination Components

MCU Section

• STM32
• Crystal
• Decoupling
• Programming Header

Keeping functional blocks together improves routing quality and simplifies debugging.

PCB Design Practices

The layout follows several common PCB design guidelines:

• Functional component grouping
• Short decoupling connections
• Short crystal routing
• Controlled impedance USB routing
• Wide power traces
• Ground stitching
• Clean routing
• Minimal unnecessary vias
• Four-layer stackup
• Continuous reference planes
• Full Design Rule Check verification

Software Used

• KiCad 9
• STM32CubeMX
• STM32CubeIDE

Current Status

• ✅ Schematic Complete
• ✅ PCB Layout Complete
• ✅ Four-Layer PCB
• ✅ USB Differential Pair Routed
• ✅ Ground Planes Implemented
• ✅ Design Rule Check Passed
• ✅ 3D Model Generated
• ✅ GitHub Documentation Complete

Future Improvements

• PCB Manufacturing
• Board Bring-up
• Firmware Development
• USB CDC Interface
• CAN Frame Decoder
• Desktop GUI
• Oscilloscope Validation
• Enclosure Design

Lessons Learned

This project provided hands-on experience with:

• USB Type-C hardware implementation
• Controlled impedance routing
• Differential pair routing
• Four-layer PCB stackups
• Ground plane design
• Decoupling strategies
• CAN Bus hardware
• STM32 hardware design
• PCB floorplanning
• PCB routing techniques
• Power integrity
• Signal integrity
• Design Rule Checks
• Design for Manufacturability
• Design for Assembly
• Professional hardware documentation using GitHub

Repository Structure

CANBUS-Sniffer-PCB/
│
├── README.md
├── LICENSE
│
├── Hardware/
│   ├── CAN_BUS_sniffer.kicad_pro
│   ├── CAN_BUS_sniffer.kicad_sch
│   ├── CAN_BUS_sniffer.kicad_pcb
│   └── ...
│
├── images/
│   ├── schematic.png
│   ├── pcb_layout.png
│   ├── pcb_layout_w_gndpours.png
│   ├── pcb_3d.png
│   └── pcb_3d_w_gndpours.png
│
├── Manufacturing/
│
└── Firmware/

License

This project is released under the MIT License.

Designed by David Valle
Electrical Engineer | PCB Design | Embedded Systems