ELM327 Bluetooth Emulator Scripts

Installation and runtime scripts for an ELM327 OBD-II emulator that presents itself over Bluetooth SPP (RFCOMM) for diagnostic clients such as GTach.

Architecture

GTach (RFCOMM) <--> bt-server.py <--> ircama ELM327 emulator (TCP 35000)

The ircama ELM327 emulator listens on TCP port 35000. A Bluetooth bridge (bt-server.py) binds RFCOMM channel 1 and relays data bidirectionally to the emulator's TCP socket.

Files

File	Purpose
install-elm327-emulator.sh	Idempotent installer: packages, scripts, systemd unit
start-elm327-emulator-bt.sh	Starts emulator + Bluetooth bridge (used by systemd unit and for manual runs)
start-elm327-emulator-tcp.sh	Starts emulator in TCP-only mode (no Bluetooth)
bt-server.py	RFCOMM-to-TCP bridge daemon
elm327-emulator.service	systemd unit for boot-time startup
status-elm327-emulator.sh	Health check: reports status of all dependent services and components

Installation

On the target Raspberry Pi (root or sudo):

git clone https://github.com/William12556/ELM327.git
cd ELM327
bash install-elm327-emulator.sh

The installer:

• Stops any running service and uninstalls any prior pip packages.
• Installs bluez, bluez-tools, python-OBD, and ELM327-emulator.
  • Pins setuptools<81 so the emulator's legacy setup.py can build.
• Copies runtime scripts to /opt/elm327/.
• Installs and enables elm327-emulator.service.
• Runs status-elm327-emulator.sh on completion.

After installation the service starts automatically on every boot. The installer is idempotent: re-running it cleans up prior state and reinstalls.

Operation

Service control

systemctl status elm327-emulator
systemctl start elm327-emulator
systemctl stop elm327-emulator
systemctl restart elm327-emulator

Status check

bash /opt/elm327/status-elm327-emulator.sh

Reports pass/fail/warn for each component in the stack:

1. systemd service state (bluetooth, elm327-emulator) and enabled status
2. Bluetooth adapter presence, UP/RUNNING flags, name, and MAC
3. Running processes (python3 -m elm, bt-server.py)
4. TCP port 35000 accepting connections
5. RFCOMM channel 1 socket
6. SDP Serial Port Profile record (informational)
7. Paired Bluetooth devices
8. Last 5 lines of bt-server.log and elm.log

Exit code 0 = all critical checks passed. Exit code 1 = one or more critical checks failed.

Run remotely from the Mac:

ssh root@ELM327-Emulator.local bash /opt/elm327/status-elm327-emulator.sh

Logs

journalctl -u elm327-emulator -f # systemd log (startup, errors)
tail -f /opt/elm327/bt-server.log # RFCOMM bridge activity
tail -f /opt/elm327/elm.log # ELM327 emulator command trace

Pairing GTach

A Bluetooth pairing handshake is required once between the GTach Pi and the emulator Pi. From the GTach Pi:

bluetoothctl
[bluetooth]# scan on# wait for ELM327-Emulator to appear
[bluetooth]# pair <MAC>
[bluetooth]# trust <MAC>
[bluetooth]# quit

Thereafter, GTach connects on RFCOMM channel 1 without prompting.

Manual start (without systemd)

systemctl stop elm327-emulator
/opt/elm327/start-elm327-emulator-bt.sh

Ctrl+C shuts the bridge and emulator down cleanly.

TCP-only mode (macOS development)

For non-Bluetooth testing from the development Mac:

systemctl stop elm327-emulator
bash /opt/elm327/start-elm327-emulator-tcp.sh

Dependencies

• python-OBD
• ELM327-emulator
• bluez 5.x

Notes

• The bridge binds with BDADDR_ANY, so it adopts whichever Bluetooth adapter is active.
• The bridge waits up to 30 s for the TCP backend before opening the RFCOMM listener; if the emulator fails to start, the service exits and systemd retries after 5 s.
• sdptool is invoked at runtime to advertise an SDP record for the SPP service. This is deprecated in bluez 5.x and will typically warn on stock Debian Bookworm; the failure is non-fatal. GTach hardcodes RFCOMM channel 1 and does not require the SDP record.

Version History

Version	Date	Description
2.2	2026-05-26	Added status-elm327-emulator.sh; installer now runs status check on completion
2.1	2026-05-26	Removed bluetoothd --compat drop-in; installer cleans up prior compat.conf
2.0	2026-05-26	Boot-time automation via systemd; hardened bt-server.py and start-elm327-emulator-bt.sh
1.1	2026-04-01	Added Usage section; documented manual start procedure
1.0	2025	Initial release

Copyright

Copyright (c) 2026 William Watson. MIT License.