Solstice

TrailCurrent Solstice

Solar gateway module that reads data from a Victron MPPT (Maximum Power Point Tracker) solar charge controller via serial and relays the readings over a CAN bus interface. Part of the TrailCurrent open-source vehicle platform.

Hardware Overview

• Board: Waveshare ESP32-S3-RS485-CAN
• Microcontroller: ESP32-S3
• Function: Serial-to-CAN bus bridge for Victron MPPT solar charge controller data
• Key Features:
  • Victron MPPT VE.Direct TEXT protocol parsing (solar data)
  • VE.Direct HEX GET polling for SmartShunt extended data (temperature, midpoint voltage, alarms, history)
  • Load control via VE.Direct HEX SET protocol over CAN
  • CAN bus output at 500 kbps
  • Real-time solar panel monitoring
  • OTA firmware updates via CAN-triggered WiFi + HTTP
  • WiFi credential provisioning over CAN bus

Hardware Requirements

Connections

See DOCS/solstice-pinout.svg for a wiring diagram of all external connections.

Components

• Board: Waveshare ESP32-S3-RS485-CAN — schematic
• CAN Bus: Built-in transceiver (TX: GPIO 15, RX: GPIO 16, 500 kbps)
• Serial: Victron MPPT VE.Direct connection via SH1.0 4-pin JST (RX: GPIO 1, TX: GPIO 2 at 19200 baud)
• Debug Console: USB CDC (115200 baud)

KiCAD Library Dependencies

This project uses the consolidated TrailCurrentKiCADLibraries.

Setup:

# Clone the library
git clone git@github.com:trailcurrentoss/TrailCurrentKiCADLibraries.git

# Set environment variables (add to ~/.bashrc or ~/.zshrc)
export TRAILCURRENT_SYMBOL_DIR="/path/to/TrailCurrentKiCADLibraries/symbols"
export TRAILCURRENT_FOOTPRINT_DIR="/path/to/TrailCurrentKiCADLibraries/footprints"
export TRAILCURRENT_3DMODEL_DIR="/path/to/TrailCurrentKiCADLibraries/3d_models"

See KICAD_ENVIRONMENT_SETUP.md in the library repository for detailed setup instructions.

Opening the Project

1. Set up environment variables (see Library Dependencies above)
2. Open KiCAD:

   kicad EDA/solstice.kicad_pro

3. Verify libraries load - All symbol and footprint libraries should resolve without errors
4. View 3D models - Open PCB and press Alt+3 to view the 3D visualization

Schematic Sheets

The design uses a hierarchical schematic with dedicated sheets:

• Root - Top-level connections
• Power - Power distribution and regulation
• CAN - CAN bus transceiver interface
• MCU - ESP32 microcontroller and support circuits
• Connectivity - Serial interface to Victron MPPT

Firmware

ESP-IDF 5.5.2 project in the main/ directory.

Setup:

# Source ESP-IDF environment
source ~/esp/v5.5.2/esp-idf/export.sh

# Set target
idf.py set-target esp32s3

# Build firmware
idf.py build

# Flash to board
idf.py -p /dev/ttyUSB0 flash

# Monitor serial output
idf.py -p /dev/ttyUSB0 monitor

Victron VE.Direct Parameters

The firmware parses the following VE.Direct TEXT protocol fields from the MPPT:

The firmware also polls the following SmartShunt registers via VE.Direct HEX GET (one every 2 seconds, ~12 s full cycle):

CAN Bus Protocol

The gateway uses the following CAN message IDs at 500 kbps:

Message 0x00 (3 bytes) - OTA trigger (received):

Triggers the device to connect to WiFi and start an HTTP OTA server for 3 minutes. Upload firmware with:

curl -X POST http://esp32-XXYYZZ.local/ota --data-binary @build/solstice.bin

Message 0x01 - WiFi credential provisioning (received):

Chunked protocol for sending WiFi SSID and password over CAN. Credentials are stored in NVS and persist across reboots. See ota.h for the protocol details.

Message 0x04 (6 bytes) - Firmware version report (transmitted once on boot):

Sent after CAN initialization. Headwaters uses this to track the running firmware version, including after OTA updates.

Message 0x2C (7 bytes) - Solar panel basics (transmitted every 33ms):

Message 0x2D (3 bytes) - Solar current:

Message 0x2E (1 byte) - Load control (received):

When a 0x2E message is received over CAN, the gateway sends a VE.Direct HEX SET command to register 0xEDAB on the MPPT to control the load output.

Message 0x2B (6 bytes) - Shunt extended live data (transmitted every 33ms):

Message 0x2F (6 bytes) - Shunt extended history (transmitted every 33ms):

Both shunt extended messages are populated by periodic VE.Direct HEX GET requests to the SmartShunt. Values update every ~12 seconds (6 registers polled at 2 s intervals).

Project Structure

├── main/                         # ESP-IDF firmware source
│   ├── main.c                    # VE.Direct parser, CAN TX/RX, load control
│   ├── ota.h                     # OTA update and WiFi provisioning header
│   ├── ota.c                     # OTA update and WiFi provisioning
│   ├── idf_component.yml         # Managed component dependencies (mdns)
│   └── CMakeLists.txt            # Component build config
├── EDA/                          # KiCAD hardware design files
│   ├── solstice.kicad_pro
│   ├── solstice.kicad_sch        # Root schematic
│   ├── can.kicad_sch             # CAN subsystem
│   ├── connectivity.kicad_sch    # Serial interface
│   ├── mcu.kicad_sch             # MCU subsystem
│   ├── power.kicad_sch           # Power subsystem
│   └── solstice.kicad_pcb        # PCB layout
├── CAD/                          # Enclosure design
│   └── trailcurrent-solstice-housing.FCStd
├── DOCS/                         # Documentation and diagrams
│   ├── solstice-pinout.svg       # External connection diagram
│   └── ESP32-S3-RS485-CAN-Schematic.pdf
├── partitions.csv                # Dual OTA partition table
├── sdkconfig.defaults            # ESP-IDF build defaults
└── CMakeLists.txt                # ESP-IDF project config

License

MIT License - See LICENSE file for details.

This is open source hardware. You are free to use, modify, and distribute these designs under the terms of the MIT license.

Contributing

Improvements and contributions are welcome! Please submit issues or pull requests.

Support

For questions about:

• KiCAD setup: See KICAD_ENVIRONMENT_SETUP.md
• Assembly workflow: See BOM_ASSEMBLY_WORKFLOW.md