Switching to CAN Transport: From WiFi to Hardware

This chapter transitions your OpenLCB node from WiFi/TCP transport (Chapter 3) to CAN bus transport—the standard physical layer for most OpenLCB networks. You’ll keep the same node code and configuration, but swap out the network interface for a hardware CAN connection via an external transceiver and a CAN bus interface module (such as RR-CirKits LCC Buffer-USB, or any compatible USB-to-CAN adapter).

Overview

In Chapter 3, we built a working OpenLCB node that communicated over WiFi via a TCP Hub. While powerful for learning and for embedded systems with network connectivity, WiFi-based OpenLCB is not the standard deployment model. Real OpenLCB networks rely on CAN (Controller Area Network), a robust, deterministic protocol designed for automotive and industrial control systems.

The good news: the OpenLCB node code barely changes. What does change is how the hardware communicates with the rest of your LCC network.

What You’ll Learn

• How CAN transceivers work and why they need external power
• The Esp32HardwareTwai class and why it’s named that (technical context for readers using other tools)
• Wiring an ESP32 to a CAN transceiver on a breadboard
• Configuring JMRI to connect via a CAN bus interface module instead of TCP
• Diagnosing CAN bus issues using TWAI status messages
• Verifying your node works the same way on CAN as it did on WiFi

Chapter Structure

This chapter assumes you’ve completed Chapters 3 and 4 (WiFi node and configuration). You’ll need:

• Hardware:
  • CAN transceiver (SN65HVD230 or MCP2551)
  • CAN bus interface module (e.g., RR-CirKits LCC Buffer-USB, or any USB-to-CAN adapter compatible with JMRI)
  • CAN bus power supply (e.g. RR-CirKits LCC Power-Point or equivalent)
  • 120Ω terminating resistors
  • breadboard
  • jumpers
• Time: ~1–2 hours depending on your familiarity with breadboard wiring
• Existing knowledge: Node code from Chapter 3, JMRI basics from Chapter 3, configuration fundamentals from Chapter 4

The sections guide you through:

1. Understanding CAN Transceivers — Open-collector design, power requirements, transceiver options
2. Hardware Wiring — Fritzing diagram and step-by-step breadboard setup
3. Code Changes — Minimal modifications to switch from WiFi to CAN
4. The Esp32HardwareTwai Class — Why it’s named that, and what’s coming in future Arduino cores
5. JMRI Reconfiguration — Disabling TCP, enabling RR-CirKits connection
6. TWAI Bus Diagnostics — Reading and interpreting status messages for troubleshooting
7. Verification — Confirming your node works the same way on CAN as it did on WiFi

Key Insight: Your OpenLCB node is transport-agnostic. The application logic (producing events every 2 seconds) is completely separate from the physical layer (WiFi vs. CAN). This is the power of good architecture—change the transport, keep the application.