Here is the list of connections between parts.

The RadiationD module power and cpm output is on the P3 connector. You might also want to remove J1 jumper to make the module silent.

Between P3 connector on RadiationD module and other parts:

P3.VCC -> POWER.+5V
P3.GND -> POWER.GND
P3.VIN -> ESP01.GPIO2

 Between ESP-01 and other parts:

ESP01.VCC    -> POWER.+3.3V
ESP01.CHPD   -> ESP01.VCC
ESP01.GND    -> POWER.GND
EPS01.GPIO02 -> P3.VIN

 Between CJMCU power supply module and other parts:

POWER.+5V	-> P3.VCC
POWER.GND	-> P3.GND
POWER.GND	-> ESP01.GND
POWER.+3.3V	-> ESP01.VCC

The code that I provided simply counts clicks from the GPIO2 and once per minute sends JSON message to predefined MQTT broker.

/// Geiger counter
#define RECEIVER_PIN 2  // 4=GPIO4=D2 any interrupt able pin (Wemos) // 2=GPIO2 on ESP-01
/// Geiger tube parameters
#define TUBE_NAME "j305"
#define TUBE_FACTOR 0.00812
/// 

TUBE_NAME will appear in the message topic.

TUBE_FACTOR is necessary to convert CPM into uSv/h. This depends on actual tube used. My module had Chinese J305 tube and for that model value 0.00812 is the conversion factor.

#include "wifipassword.h"
//#define WIFIPASSWORD "12345secret"
const char* myhostname = "esp01geiger";
const char* ssid = "Springfield";
const char* password =  WIFIPASSWORD;
const char* mqttServer = "iotlocal.lan";
const uint32_t mqttPort = 1883;

 "Springfield" and password defined in WIFIPASSWORD are my WiFi network parameters.

I'm using broker running in my LAN available at iotlocal.lan address, listening on port 1883.

"esp01geiger" is a friendly hostname to make it easier to recognize the device in Arduino IDE OTA (over-the-air) update and on my router summary page.

For debug purposes there are some messages sent over the serial port.

const char* mqttPrefix = "esphome"; 

This is topic prefix under which all messages coming from sensors in my setup appear.

You need Arduino IDE with following libraries installed:

• ArduinoOTA - for updating firmware over-the-air
• ArduinoJSON - for easy and reliable formatting of JSON objects
• PubSubClient - for MQTT connectivity

After powerup the module will announce that it works:

# mosquitto_sub -t '#' -h iotlocal.lan -v

esphome/sensor/f4f8e5/connection online

"esphome" is my topic prefix, "f4f8e5" is the ESP8266 ID, this is also part of the device's MAC address

Then each minute an update will be posted:

esphome/sensor/j305/state {"receiver":"f4f8e5","cpm":22,"usv_per_h":0.17864}

 "j305" is the TUBE_NAME predefined in the code. The message is a single JSON document with following fields:

• receiver - id of receiver, you may have several devices with different tubes
• cpm - raw number of clicks per minute
• usv_per_h - cpm recalculated into µSv/h so that different tubes can be compared and you can monitor safety in your environment

Here is a snippet from Home Assistant configuration file that integrates radiation sensor into home automation:

sensor:
  - platform: mqtt
    name: Promieniowanie
    state_topic: "esphome/sensor/j305/state"
    unit_of_measurement: 'µSv/h'
    expire_after: 120
    availability_topic: "esphome/sensor/f4f8e5/connection"
    value_template: "{{ value_json.usv_per_h }}"

Values from the sensor will be recorded and shown in Home Assistant interface:

This can be used as input to HA scripts and automations.