Shady Elm

A bridge that connects ELM327 / STN1170 CAN adapters to SavvyCAN using the GVRET protocol over TCP. Also supports file-only logging in GVRET CSV or CRTD format.

Install

Requires Python 3.8+ and pyserial:

pip install pyserial

Quick start

# HS-CAN (500 kbps, 11-bit) on COM3, listening on 127.0.0.1:23
python savvycan_bridge.py --config STN1170_HSCAN_500000 -p COM3

# Ford MS-CAN (125 kbps)
python savvycan_bridge.py --config STN1170_MSCAN_125000 -p COM3

In SavvyCAN: connect as GVRET to 127.0.0.1:23.

For file-only logging (no SavvyCAN):

python savvycan_bridge.py -p COM3 --file-only --output-file capture.bin --format binary

See python savvycan_bridge.py --help for the full option list.

Configuration profiles

JSON files in configs/ provide reusable adapter settings. Pass --config <name> (without .json) or --config path/to/file.json. Legacy aliases STN1170_HSCAN and STN1170_MSCAN_Ford are still accepted.

Profile	Bus	Bitrate	Frame IDs
STN1170_HSCAN_500000	HS-CAN	500 kbps	11-bit
STN1170_MSCAN_125000	MS-CAN	125 kbps	11-bit

To add a profile, drop a JSON file in configs/ with serial, can, and device sections — see the existing files for shape.

Output formats

• binary — GVRET binary (default; required for live SavvyCAN streaming)
• gvret — GVRET CSV (text, human-readable, compatible with SavvyCAN file import)
• crtd — CRTD text log

Supported adapters

• ELM327 — standard OBD-II CAN adapters
• STN1170 — adds flow control, ID filtering, and monitor modes

The STN profiles use raw CAN presets (STP 31 for HS-CAN, STP 51 for MS-CAN) and start monitoring with STM, falling back to STMA/ATMA for adapters that do not support raw STN monitoring.

Troubleshooting

• Port unavailable — close other apps holding the port; run with --list-ports to confirm the device is present.
• Init failed — try --debug to see the adapter's responses, or --skip-init if the adapter is already configured externally.
• No frames — verify CAN-bus wiring, make sure the STN profile uses raw STP 31/STP 51 plus STM, and try --debug to inspect raw serial.
• Garbled data — recheck --baud and flow control (--test-flow-control probes available modes).

Use --env-check to print Python and pyserial versions.

Testing

python -m pytest tests/

Layout

• savvycan_bridge.py — bridge entrypoint
• configs/ — adapter profiles
• tests/ — pytest suite
• docs/ — protocol notes