MQTT Integration

The MultiGeiger firmware supports MQTT publishing (available since firmware 1.18+). This allows real-time streaming of radiation measurements and sensor data to any MQTT broker.

Configuration

MQTT can be configured via the web interface at /config:

• Send to MQTT: Enable/disable MQTT publishing

• MQTT host: Broker hostname or IP address (e.g., mqtt.example.com or 192.168.1.100)

• MQTT port: Broker port (default: 1883 for plain, 8883 for TLS)

• Use TLS: Enable encrypted connection (PoC implementation, uses insecure mode without certificate validation)

• Retain MQTT messages: Set retain flag on published messages

• MQTT username: Authentication username (leave empty for no auth)

• MQTT password: Authentication password

• Base topic: Custom base topic prefix (optional, defaults to device name ESP32-XXXXXX)

Topic Structure

All messages are published under the configured base topic. The default structure is:

<baseTopic>/live/<metric>
<baseTopic>/status

Where <baseTopic> is either the configured custom base topic or the device name (e.g., ESP32-51564452).

Published Topics

Live Measurement Data

These topics are published during each measurement cycle (every 150 seconds by default):

Topic	Data Type	Description
live/count_rate_cps	float (3 dec)	Current count rate in counts per second
live/dose_rate_uSvph	float (3 dec)	Current dose rate in µSv/h
live/counts	integer	Number of GM tube counts in this interval
live/cpm	integer	Counts per minute
live/dt_ms	integer	Measurement interval in milliseconds
live/hv_pulses	integer	High voltage pulses (HV circuit health)
live/accum_counts	integer	Accumulated counts since boot
live/accum_time_ms	integer	Accumulated measurement time in milliseconds
live/accum_rate_cps	float (3 dec)	Accumulated average rate in CPS
live/accum_dose_uSvph	float (3 dec)	Accumulated average dose rate in µSv/h
live/tube_type	string	Geiger-Müller tube type (e.g., “Si22G”)
live/tube_id	integer	Tube type ID number
live/timestamp	integer	UTC Unix timestamp

Environmental Sensor Data (Optional)

If a BME280/BME680 sensor is connected, these additional topics are published:

Topic	Data Type	Description
live/temperature	float (2 dec)	Temperature in degrees Celsius (°C)
live/humidity	float (2 dec)	Relative humidity in percent (%)
live/pressure	float (2 dec)	Atmospheric pressure in hectopascals (hPa)

Status Information

Topic	Data Type	Description
status	JSON object	Complete status information (see below)

The status topic contains a JSON object with all current measurements and system status:

{
  "wifi_status": 1,
  "mqtt_connected": true,
  "last_publish_ms": 123456,
  "counts": 42,
  "cpm": 17,
  "hv_pulses": 150,
  "dt_ms": 150000,
  "have_thp": true,
  "timestamp": "2025-01-15T12:34:56Z"
}

JSON Fields:

• wifi_status: WiFi connection status code (0=off, 1=connected, 2=error, 3=connecting, 4=AP mode)

• mqtt_connected: MQTT broker connection status (boolean)

• last_publish_ms: Milliseconds since last successful publish

• counts: GM tube counts in this measurement

• cpm: Counts per minute

• hv_pulses: High voltage pulses

• dt_ms: Measurement interval in milliseconds

• have_thp: Whether environmental sensor data is available (boolean)

• timestamp: UTC timestamp string

Example Configuration

Home Assistant

Here’s an example Home Assistant MQTT sensor configuration for the MultiGeiger:

mqtt:
  sensor:
    - name: "MultiGeiger Dose Rate"
      state_topic: "ESP32-51564452/live/dose_rate_uSvph"
      unit_of_measurement: "µSv/h"
      value_template: "{{ value | float }}"

    - name: "MultiGeiger CPM"
      state_topic: "ESP32-51564452/live/cpm"
      unit_of_measurement: "CPM"
      value_template: "{{ value | int }}"

    - name: "MultiGeiger Temperature"
      state_topic: "ESP32-51564452/live/temperature"
      unit_of_measurement: "°C"
      device_class: temperature
      value_template: "{{ value | float }}"

Node-RED

Example Node-RED flow to subscribe and process MultiGeiger MQTT data:

[
  {
    "id": "mqtt-in",
    "type": "mqtt in",
    "topic": "ESP32-51564452/live/#",
    "broker": "mqtt-broker-id",
    "name": "MultiGeiger Data"
  }
]

Troubleshooting

MQTT not publishing:

1. Check that “Send to MQTT” is enabled in the web config

2. Verify MQTT broker hostname/IP and port are correct

3. Check authentication credentials if your broker requires auth

4. Monitor serial output for MQTT connection status messages

5. Verify WiFi is connected (MQTT requires active WiFi connection)

TLS connection fails:

• The current TLS implementation is a proof-of-concept using insecure mode (no certificate validation)

• Some brokers may reject insecure TLS connections

• For production use, consider using plain MQTT or setting up proper certificate validation

Messages not retained:

• Enable “Retain MQTT messages” in the web configuration

• Note that retained messages persist on the broker until explicitly cleared

QoS and Reliability

• Current implementation uses configurable QoS (Quality of Service) level

• Default QoS can be set in configuration

• Messages are published every measurement cycle (default: 150 seconds)

• If MQTT broker is unreachable, messages are not queued (they are skipped)

• Connection is automatically retried every 5 seconds

Technical Notes

• Client ID: MultiGeiger-<baseTopic> (slashes removed)

• Buffer Size: 512 bytes

• Reconnect Interval: 5 seconds

• TLS Mode: Insecure (skips certificate validation) - PoC only

• Message Format: Simple value strings for individual metrics, JSON for status

• Timestamp Format: Unix epoch time (seconds since 1970-01-01 00:00:00 UTC)