Custom MQTT Guide

This is a guide on how to use your FCS with your own custom MQTT broker, in order to set it up with Home Assistant or other custom solutions.

Introduction

The FCS custom MQTT integration works with Home Assistant (HA).

Enter your Home Assistant MQTT broker credentials in FCS. Home Assistant then detects and configures FCS automatically.

You can also use another MQTT broker with Node-RED or a custom application.

If you decide to use a custom MQTT broker, you will not be able to use brewtools.cloud simultaneously.

Before you start

1. Connect FCS to your network.

2. Configure an MQTT broker and create credentials for FCS.

3. Enter the broker credentials in FCS.

Use the same broker for Home Assistant and FCS. Home Assistant must have MQTT configured.

Typical MQTT JSON payload from FCS Fermentation

FCS publishes device data to fcs-fermentation/<mcu_id>/state.

The following example uses a standard 24V, 2A setup. It has one temperature sensor and one pressure sensor. Connected density and level sensors add their related fields.

Subscribe to fcs-fermentation/# to find your mcu ID. Then subscribe to its state topic. For example:

fcs-fermentation/20414116222657176/state

All MQTT values use fixed units: temperature uses Celsius, pressure uses bar, density uses SG, volume uses liters and AC/DC current uses ampere.

{
  "mcu_id": "20414116222657176",
  "temperature_1": 25.109434127807617,
  "temperature_2": null,
  "temperature_selected_sensor_value": 25.109434127807617,
  "temperature_setpoint": 50,
  "current_total": 0.15119613707065582,
  "current_display": 0.10309077054262161,
  "current_relay_1": 0.00043160573113709688,
  "current_relay_2": 0.00043160573113709688,
  "current_can_1": 0.01646907813847065,
  "current_can_2": 0.000896490819286555,
  "state_relay_1": 0,
  "state_relay_2": 0,
  "state_can_1": 1,
  "state_can_2": 1,
  "pressure": 0.0013385240454226732,
  "pressure_setpoint": 0,
  "current_relay_3": 0.00043160573113709688,
  "current_relay_4": 0.00043160573113709688,
  "current_can_3": 0.000896490819286555,
  "current_can_4": 0.000894834694918245,
  "state_relay_3": 0,
  "state_relay_4": 0,
  "state_can_3": 1,
  "state_can_4": 1,
  "external_relay_state": 0,
  "current_acc_1": 0,
  "current_acc_2": 0
}

Payload fields

Field	Description
mcu_id	Unique FCS mcu ID.
temperature_1, temperature_2	Temperature sensor readings in Celsius. A disconnected or unavailable sensor returns null.
temperature_selected_sensor_value	Temperature used by the control system in Celsius.
temperature_setpoint	Configured temperature target in Celsius.
pressure	Measured pressure in bar.
pressure_setpoint	Configured pressure target in bar.
current_total, current_display	Total system and display current readings in ampere.
current_relay_*, current_can_*	Current readings for relay and CAN connections in ampere.
current_acc_*	AC current readings in ampere.
state_relay_*, state_can_*, external_relay_state	State values for relay, CAN, and external relay connections.

Connected hardware determines which fields appear in the payload. Handle missing fields and null values in custom integrations.

Updating Control System Setpoints

Publish a numeric payload to update a control system setpoint:

• fcs-fermentation/<mcu_id>/set/temperature_setpoint

• fcs-fermentation/<mcu_id>/set/pressure_setpoint

FCS enforces the allowed ranges. Subscribe to fcs-fermentation/<mcu_id>/state to confirm the updated value.

Example payloads

Temperature: 0–85 °C (32–185 °F)

18

Pressure: 0–2 bar (0–29 psi)

0.8

Auto Detected FCS Fermentation Device on HA Server

The image below shows a correctly detected FCS Fermentation device in Home Assistant.