cul2mqtt

Interface between a Busware CUL / COC / SCC / CUNO running culfw and MQTT 📡 — FS20, EM1000, HMS, S300TH, FHT, MAX!, ... with Home Assistant discovery

Built on the cul library and mqtt-interfaces-core.

Upgrading from 0.1.x? Topics changed — see CHANGELOG.md.

Getting started

Install and run

npm install -g cul2mqtt
cul2mqtt --serialport /dev/ttyACM0 --mqtt-url mqtt://192.168.1.2

The user running cul2mqtt needs access to the serial port (usually group dialout). Received telegrams show up as cul/status/<protocol>/<address>/<field> right away; -v debug prints the raw traffic (cul < / cul >).

cul2mqtt --help lists all options; every option can also be set via an environment variable (CUL2MQTT_SERIALPORT, CUL2MQTT_MQTT_URL, CUL2MQTT_NAME, ...).

option	default	description
-s, --serialport	/dev/ttyACM0	serial port of the CUL / COC / SCC, or auto (see above)
--discover		list the busware sticks on this host and exit (--discover-json for JSON)
--baudrate	9600	serial baud rate (38400 with --coc / --scc)
-c, --cul-mode	SlowRF	RF mode: SlowRF (FS20, HMS, EM, S300TH, FHT, ...), MORITZ (MAX!) or AskSin
--coc, --scc	off	device is a Busware COC / SCC on a Raspberry Pi
--host, --port	, 2323	CUNO / CUNO2 via telnet instead of a serial port
-m, --map-file		JSON file with friendly item names (see below)
--fht-central		FHT central code (4 hex digits), required for cul/set/fht
--offline-detection	on	mark silent devices offline on cul/status/<protocol>/<address>/online
--learn-intervals	on	widen offline timeouts from observed per-device message gaps
--state-dir	$STATE_DIRECTORY	directory for persisted state (learned intervals); set by systemd
--publish-raw	off	additionally publish every raw culfw line on cul/raw
--raw-set	off	accept raw culfw commands on cul/set/raw (see below)
-u, --mqtt-url	mqtt://localhost	broker URL, see MQTT.js
--mqtt-username, --mqtt-password		broker credentials
-n, --name	cul	instance name, used as topic prefix
--json-payloads	on	status as {"val", "ts", "lc"} JSON; --no-json-payloads for plain values
--ha-discovery	on	Home Assistant MQTT discovery (--no-ha-discovery disables and clears it)
--ha-prefix	homeassistant	discovery prefix
--no-maintenance	(on)	disable the maintenance/set/loglevel and restart topics (see below)
--mqtt-client-id-prefix		prefix for the mqtt client id
--mqtt-tls-ca		CA certificate file for mqtts:// brokers
--config-schema		print a JSON Schema of all options and exit
-v, --verbosity	info	error, warn, info, debug

Finding the stick

cul2mqtt --discover

lists the busware sticks plugged into this host — udev has already named them, so there is nothing to scan:

/dev/serial/by-id/usb-busware.de_CUL868-if00  → /dev/ttyACM0  (serial)

Use the by-id path rather than /dev/ttyACM0: it survives a replug and a reboot, while the ttyACM number can swap with another stick's. -s auto does that for you — it runs the same scan at start and opens the stick it found, refusing to start when none or more than one busware CUL is plugged in rather than talking to the wrong radio:

cul2mqtt -s auto -u mqtt://192.168.1.2

Only sticks whose name contains both busware and CUL are recognised — that is what a CUL433/CUL868 looks like in /dev/serial/by-id. A CUN or COC, a nanoCUL, or any other vendor's culfw clone is named differently: give those to --serialport directly. A CUNO on the network is --host instead.

Docker

Multi-arch image (amd64, arm64, armv7):

docker run -d --name cul2mqtt --restart unless-stopped --device /dev/ttyACM0 --group-add $(stat -c %g /dev/ttyACM0) \
  -e CUL2MQTT_SERIALPORT=/dev/ttyACM0 -e CUL2MQTT_MQTT_URL=mqtt://192.168.1.2 \
  ghcr.io/hobbyquaker/cul2mqtt

--device passes the CUL through, --group-add gives the unprivileged container user the serial port's group. A map file can be mounted and referenced with CUL2MQTT_MAP_FILE.

Run as a systemd service

sudo cul2mqtt --install --name cul --serialport /dev/ttyACM0 --mqtt-url mqtt://192.168.1.2

--install creates a system user cul2mqtt (member of dialout for the serial port), writes the given options to /etc/cul2mqtt/<name>.env (CUL2MQTT_* variables — edit and systemctl restart cul2mqtt@<name> to change), installs the template unit /etc/systemd/system/cul2mqtt@.service and enables + starts cul2mqtt@<name>. The instance name is the --name option, i.e. the MQTT topic prefix. Logs: journalctl -u cul2mqtt@<name> -f.

Several CULs (e.g. one in SlowRF and one in MORITZ mode): run --install once per device with a different --name — each becomes its own instance cul2mqtt@<name> with its own config and topic prefix, sharing one template unit and one system user:

sudo cul2mqtt --install --name cul  --serialport /dev/ttyACM0 --mqtt-url mqtt://broker
sudo cul2mqtt --install --name max  --serialport /dev/ttyACM1 --cul-mode MORITZ --mqtt-url mqtt://broker
systemctl status 'cul2mqtt@*'

sudo cul2mqtt --uninstall --name max removes one instance (the template unit goes with the last one).

Tip: with several USB serial devices use a stable path like /dev/serial/by-id/usb-busware.de_CUL868-if00 instead of /dev/ttyACM0.

Deploy to a host (developers)

deploy.sh [user@host] packs the module, copies it to the host, installs it under /usr/local/lib/node_modules/cul2mqtt and restarts every cul2mqtt@<name> service there (SERVICE, REMOTE_DIR, SKIP_TESTS env vars, see the script). Install the service once with --install first.

Topics

Topics and payloads follow the mqtt-smarthome architecture. cul is the instance name (--name).

cul/connected

Retained. 0 = cul2mqtt is not running (set via last will), 1 = connected to the broker but the CUL is not open (unplugged, wrong port, telnet down — retried every 10 s), 2 = connected to both.

cul/status/<protocol>/<address>/<field>

One retained item per parsed value. Every status is {"val": <value>, "ts": <ms received>, "lc": <ms last changed>} (mqtt-smarthome); with --no-json-payloads the plain value is published instead. Protocol names are lower case, field names snake_case; rssi is published alongside when the CUL reports it.

protocol	devices	example topics
fs20	FS20 remotes, sensors, actuators	cul/status/fs20/6C4800 — the received command (on, off, toggle, dim50%, ...) as an event, not retained; cul/status/fs20/6C4800/time for timer commands
em	EM1000 power / gas / water meters	cul/status/em/0205/current, cul/status/em/0205/total, cul/status/em/0205/peak
ws	S300TH, KS300, ...	cul/status/ws/1/temperature, cul/status/ws/1/humidity
hms	HMS100T, HMS100TF, ...	cul/status/hms/A5E3/temperature, cul/status/hms/A5E3/humidity, cul/status/hms/A5E3/battery
fht	FHT80b thermostats	cul/status/fht/1234/measured_temp, cul/status/fht/1234/desired_temp, cul/status/fht/1234/actuator
moritz	MAX! (--cul-mode MORITZ)	cul/status/moritz/0A1B2C/measured_temperature, cul/status/moritz/0A1B2C/valveposition, cul/status/moritz/0A1B2C/isopen

What exactly is published depends on the parsers in the cul library.

cul/info (retained JSON) describes the running instance: adapter name and version, implemented mqtt-smarthome spec version, node version, host, pid, start time, whether maintenance topics are on.

Map file

--map-file names.json replaces addresses with friendly names. Keys are item prefixes (<protocol>/<address> or <protocol>/<address>/<field>, case-insensitive), values the name that replaces the matched part:

{
  "EM/0205": "power_dishwasher",
  "FS20/6C4800": "doorbell",
  "WS/1": "living_room",
  "WS/4/temperature": "garden_temperature"
}

→ cul/status/power_dishwasher/current, cul/status/doorbell (event), cul/status/living_room/temperature, cul/status/garden_temperature. See example-map.json.

A value may also be an object: {"name": "power_dryer", "timeout": 900} — name renames as above, timeout sets the offline detection timeout in seconds for that device (see below).

cul/status/<protocol>/<address>/online

Retained, 1/0. Offline detection (on by default, --no-offline-detection disables it): a device that stays silent longer than its timeout is marked offline. The timeout per device is, in order of precedence:

1. an explicit timeout (seconds) in the map file object value — always wins, disables interval learning for that device; 0 turns detection off for the device.
2. self-learned from the observed message gaps — only ever wider than the protocol default (median of the recent gaps × 3, or the largest recent gap × 1.5, whichever is larger), so devices that send slower or lose more messages than expected don't flap. Disable with --no-learn-intervals.
3. a lenient per-protocol default: EM, WS and HMS 30 min, FHT 60 min. SlowRF reception routinely loses several transmissions in a row, so a missed cycle or three is normal, not offline.

Event-only protocols (FS20 remotes ring when someone presses them, not on a schedule) are never marked offline unless a map file timeout opts them in. Learned intervals and last-seen times are persisted in --state-dir (systemd sets $STATE_DIRECTORY=/var/lib/cul2mqtt/<name>; without a state dir learning starts over on restart).

cul/set/fs20/<address>

Sends an FS20 command. <address> is housecode + address as 6 hex digits (6C4800) or <housecode>/<address> (6C48/00, ELV notation works too). Payload is a plain value or mqtt-smarthome style JSON ({"val": "on"}):

payload	sends
on, off, true, false, 1, 0	on / off
0..100	nearest dim step (dim06% ... dim100%, 0 = off)
toggle, dimup, dimdown, dimupdown, on-for-timer, off-for-timer, sendstate, reset, ...	the FS20 command as culfw names it
{"cmd": "on-for-timer", "time": 120}	command with a timer in seconds
11..ff (2 hex digits)	raw FS20 command byte

mosquitto_pub -t cul/set/fs20/6C4800 -m on
mosquitto_pub -t cul/set/fs20/6C4801 -m 50
mosquitto_pub -t cul/set/fs20/6C4802 -m '{"cmd": "on-for-timer", "time": 300}'

cul/set/fht/<device>/<command>

Sends an FHT command (desired-temp, mode, day-temp, night-temp, ... as in culfw); needs --fht-central <code>. The payload is the value, alternatively JSON {"cmd": "desired-temp", "value": 21.5} on cul/set/fht/<device>.

mosquitto_pub -t cul/set/fht/1234/desired-temp -m 21.5

cul/set/raw

With --raw-set, any culfw command line is written to the CUL (F6C480011, X21, ...). This is an unrestricted RF transmitter — protect your broker with authentication/ACLs before enabling it. --publish-raw does the opposite: every line received from the CUL is published on cul/raw (not retained), useful for unsupported protocols.

cul/maintenance/set/<command>

command	payload
loglevel	error, warn, info or debug	change the log level at runtime (e.g. to see cul >/cul < traffic without a restart)
restart	anything	graceful shutdown (connected 0) and exit 0; systemd (Restart=always) / Docker restart

Anyone who can publish to your broker can use these. Use broker authentication and ACLs, or disable them with --no-maintenance.

Home Assistant

MQTT discovery is on by default (HA ≥ 2024.11, device-based discovery). Every RF address the CUL hears becomes its own HA device — ws/1 or, with a map file, living_room — with a sensor per field (temperature, humidity, signal strength, power etc. get the matching device class and unit; booleans like open or battery_low become binary sensors) and the manufacturer/model derived from the protocol (ELV S300TH, ELV EM1000, ELV FHT80b, eQ-3 MAX!, ...). The devices are linked to the CUL itself, which appears as a bridge device with a Connected diagnostic. Devices are announced as they show up on air (each address has to send once); availability follows cul/connected — and, with offline detection (the default), the per-device online item: a device that stops sending becomes unavailable in HA on its own.

FS20 is receive-only for the CUL, so actuators cannot be discovered and no switches are created automatically; an FS20 remote appears as a device with one sensor holding the last command. --no-ha-discovery disables discovery and removes all announcements on startup; --ha-prefix changes the discovery prefix.

Notes

• An unplugged or busy CUL is logged once at warn; the connection is retried every 10 s and cul/connected goes back to 2 when it is back. CUNO (telnet) connections have a watchdog; a silent link is reconnected the same way.
• The RF protocol parsing lives in the cul library (1.x) — its README lists the supported devices and the parsed fields per protocol. Open parser issues there, with the raw line from -v debug or cul/raw. Messages it has no parser for are logged at debug only.
• serialport ships prebuilt binaries, so npm install -g cul2mqtt needs no compiler on the Raspberry Pi.
• Under systemd the log goes to the journal without timestamps and with proper priorities (journalctl -u cul2mqtt@<name> -p warning).

License

Licensed under GPLv2

Copyright (c) 2015–2026 Sebastian Raff hobbyquaker@gmail.com