MightyOhm Geiger Counter Kit + ESP8266 (WEMOS D1 mini) https://mightyohm.com/blog/products/geiger-counter/

geiger.ino

// get config.h from Adafruit IO example sketch and fill in your details
#include "config.h"

#include <Pins_Arduino.h>
#include <SoftwareSerial.h>
#include <Regexp.h>

AdafruitIO_Feed *cpm_feed = io.feed("Geiger CPM");
AdafruitIO_Feed *cps_feed = io.feed("Geiger CPS");
AdafruitIO_Feed *usv_feed = io.feed("Geiger uSv/hr");

SoftwareSerial geiger(D2, D3);

void setup() {
  Serial.begin(115200);

  while (! Serial);

  Serial.print("Connecting to Adafruit IO");

  io.connect();

  while (io.status() < AIO_CONNECTED) {
    Serial.print(".");
    delay(500);
  }

  Serial.println();
  Serial.println(io.statusText());

  geiger.begin(9600);
  geiger.setTimeout(10);
}

void loop() {
  io.run();

  String line = geiger.readStringUntil('\n');
  char buf[line.length()];
  line.toCharArray(buf, line.length());

  MatchState ms;
  ms.Target(buf);
  char result = ms.Match ("CPS, (%d+), CPM, (%d+), uSv/hr, (%d+.%d+)");
  if (result == REGEXP_MATCHED) {
    Serial.println(line);

    int cps = atoi(ms.GetCapture(buf, 0));
    int cpm = atoi(ms.GetCapture(buf, 1));
    float usv = atof(ms.GetCapture(buf, 2));

    cps_feed->save(cps);
    cpm_feed->save(cpm);
    usv_feed->save(usv);
  }
}

Brown = ground
Red = 3.3V
Orange = RX (pin D2 in above sketch)