Usage

OLED display

Top line

Left: Time since power-on (not shown on small displays).

Right: Overall average radiation since power-on.

Middle area

Current CPM (counts per minute) displayed using a rather big font.

Bottom line

This is a status display with 8 positions, numbered 0..7:

Rules of thumb:

  • . usually means “off” or “unused”.

  • if you see some number (0 .. 7) within the status display line, something went wrong.

Positions:

  • 0: WiFi

    • A: AccessPoint active

    • w: WiFi client trying to connect

    • W: WiFi client connected

    • 0: some error happened

  • 1: unused (formerly sensor.community)

    • .: off (not configured, not enabled)

  • 2: unused (formerly madavi)

    • .: off (not configured, not enabled)

  • 3: TTN (“The Things Network”)

    • .: off (not configured, not enabled, no LoRa hardware)

    • ?: init (enabled, before 1st transmission)

    • T: sending

    • t: idle (shown after successful sending)

    • 3: sending failed (shown after trying to send)

  • 4: BLE (Bluetooth® Low Energy)

    • .: off (not enabled)

    • ?: init (enabled, before setup of BLE service)

    • B: connected and sending notifications, if requested by connected device

    • b: connectable (advertising and ready to connect)

    • 4: BLE error

  • 5: unused

  • 6: unused

  • 7: High-Voltage Capacitor charging

    • H: OK

    • 7: failure to charge HV capacitor

ESP32 buttons

The MultiGeiger ESP32 microcontroller board has 2 buttons:

  • RST: reset (restarts device)

  • PRG: program (press and hold PRG, press RST momentarily, upload firmware)

Often, using PRG is not needed for flashing firmware, because it “just works” when using the right tools.

DIP Switches

Optionally, the MultiGeiger can be equipped with a 4-contact DIP switch under the ESP32 microcontroller board.

The firmware makes use of these 4 switches as defined in the Switches data type in switches.h:

  • SW0: Speaker on

  • SW1: Display on

  • SW2: LED on

  • SW3: BLE on

BLE - Bluetooth® Low Energy

BLE Heart Rate Service

The MultiGeiger provides a Bluetooth® Low Energy (BLE) service to allow the collection of the Geiger-Mueller count rate via a GATT Heart Rate Service (Service UUID 0x180D). The following characteristics are used:

  • 0x2A37 (‘Heart Rate Measurement Characteristic’):

    • The first byte is a collection of status flags, according to the service’s standard

    • ‘Heart Rate Measurement’ as 16 bit value (little endian), corresponds to Geiger-Mueller counts per minute (CPM)

    • ‘Energy Expenditure’ as 16 bit value (little endian), represents a rolling packet counter

  • 0x2A38 (‘Heart Rate Sensor Position Characteristic’)

    • ‘Sensor Position’ as 8 bit value, corresponds to TUBE-TYPE, allowing the conversion of CPM to radiation rate

  • 0x2A39 (‘Heart Rate Control Point Characteristic’)

    • Write characteristic, required by service’s standard to reset Energy Expenditure to 0. Writing 0x01 resets the rolling packet counter to 0.

Testing BLE

Any decent Bluetooth® scanning app should be able to connect to the device and show the notification values.

The MultiGeiger companion app was specifically made for the MultiGeiger.

There are also some generic apps:

Any other heart monitor app / device should be able to connect to the MultiGeiger, too.

  • Figure 1: Connect to the MultiGeiger with the name ‘ESP32-<id>’, where <id> should be the same ID (7 to 8 digits) as with the access point to set the device up initially.

  • Figure 2: Find the correct service (UUID 0x180D) and, if needed, load / open characteristics.

  • Figure 3: Find the Heart Rate Measurement Characteristic (UUID 0x2A37) and click on the icon to start notifications.

While testing, please keep in mind that an update packet is sent only every ~10s (along with a display refresh, if enabled). If a WiFi transmission is blocking display and BLE updates, the interval may be even longer. So it might take a while until a reaction with actual data can be seen in the app.

Fig. 1

ble1

Fig. 2

ble2

Fig. 3

ble3

MQTT Publishing

The MultiGeiger can publish measurement data to an MQTT broker in real-time. This enables integration with home automation systems like Home Assistant, IoT platforms, and custom data logging solutions.

For detailed MQTT configuration, topic structure, and integration examples, see the dedicated MQTT Integration page.

Quick overview:

  • Configuration: Via web interface at /config under “MQTT Settings”

  • Topics: All data published under <baseTopic>/live/<metric> (e.g., ESP32-51564452/live/dose_rate_uSvph)

  • Data types: Radiation measurements (CPM, dose rate), environmental data (temperature, humidity, pressure), system status

  • Update interval: Same as HTTP transmission (default: 150 seconds)

  • Features: TLS support, authentication, configurable QoS, retained messages

Note: MQTT publishing does not have a dedicated status indicator on the OLED display. Connection status is logged via serial output and available in the status JSON topic.