QSH Modbus Sniffer

Passive Modbus RTU sniffer for the **Octopus Energy Cosy heat pump.

Captures all traffic between the Cosy Hub (master) and outdoor unit (slave) via a Waveshare RS485-to-WiFi gateway in transparent transmission mode. Publishes decoded register values to Home Assistant via MQTT auto-discovery.

Features

• Passive sniffing — zero interference with the bus, no active polling
• Auto-discovery — registers appear automatically as HA sensors
• Robust reconnection — exponential backoff on gateway disconnection
• S6 process supervision — auto-restart on crash
• CSV logging — full frame-level logs for analysis
• Operating state detection — tracks ACTIVE / HEARTBEAT / IDLE modes
• Signed int16 handling — correct negative temperature values

Hardware Required

• Waveshare RS485-to-WiFi gateway (transparent mode, 19200 baud 8N1)
• Wired in parallel to the RS485 bus between Cosy Hub and outdoor unit

Register Map

Registers are published as sensor.qsh_modbus_sniffer_* entities. See identified.md for full details and evidence, unknown.md for registers under investigation.

Register	Name	Scale	Unit	Confidence
27	Electrical Power In	×1	W	CONFIRMED (r=0.999 vs Shelly EM)
29	HP LWT	×0.1	°C	CONFIRMED
30	Condenser Temp	×0.1	°C	REVISED
36	T1 External Temp	×0.1	°C	CONFIRMED (r=1.000 vs API)
38	Internal Unit Temp	×0.1	°C	STATISTICAL
39	Outdoor Ambient Temp	×0.1	°C	STATISTICAL
40	System Return Temp	×0.1	°C	CONFIRMED (tracks Shelly return)
45	Discharge Gas Temp	×0.1	°C	STATISTICAL (r=0.922 vs flow)
47	Flow Rate	×0.01	l/min	NAMED
50	Reported COP	×0.01	—	STATISTICAL (mean 4.23)
51	Compressor Speed	×1	%	STATISTICAL
53	Compressor Frequency	×0.1	Hz	STATISTICAL
64	Heat Output	×1	W	CONFIRMED (r=0.999 vs flow×ΔT)
66	Operating Mode	×1	enum	STATISTICAL
91	Target Flow Temp	×0.1	°C	CONFIRMED

Configuration

Option	Default	Description
gateway_host	192.168.2.73	Waveshare gateway IP
gateway_port	8899	Gateway TCP port
mqtt_host	(auto)	MQTT broker (auto-detected from HA if empty)
mqtt_port	1883	MQTT port
mqtt_user	(auto)	MQTT username
mqtt_pass	(auto)	MQTT password
publish_interval	5	Seconds between MQTT publishes
debug	false	Enable debug logging

Useful Template Sensors

# CoP calculation
template:
  - sensor:
      - name: "Cosy CoP"
        unit_of_measurement: ""
        state: >
          {% set heat = states('sensor.qsh_modbus_sniffer_cosy_heat_output') | float(0) %}
          {% set power = states('sensor.qsh_modbus_sniffer_cosy_electrical_power_in') | float(0) %}
          {% if power > 50 %}
            {{ (heat / power) | round(2) }}
          {% else %}
            0
          {% endif %}

Logs

CSV logs are written to /data/modbus_logs/ inside the add-on container, accessible via the share mount. Each day gets a separate file: modbus_YYYY-MM-DD.csv.