This gist drives a SSD1306 OLED with values coming from a ESP8266 (Wemos D1 Mini) given by a DHT22 temp/humidity sensor.

oled_thermo.ino

/**************************************************************************
  This is an example for our Monochrome OLEDs based on SSD1306 drivers

  Pick one up today in the adafruit shop!
  ------> http://www.adafruit.com/category/63_98

  This example is for a 128x32 pixel display using I2C to communicate
  3 pins are required to interface (two I2C and one reset).

  Adafruit invests time and resources providing this open
  source code, please support Adafruit and open-source
  hardware by purchasing products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries,
  with contributions from the open source community.
  BSD license, check license.txt for more information
  All text above, and the splash screen below must be
  included in any redistribution.
 **************************************************************************/

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Fonts/FreeMono9pt7b.h>
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <Arduino_JSON.h>
#include <DHT.h>

#define DHTPIN 0 // Arduino!
uint8_t DHTPin = D3;
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

float humidity, temperature, dewpoint;

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

const char* SSID = "yourSSID";
const char* PSK = "yourWifiPassword";
const char* MQTT_BROKER = "yourMQTTHostIP";
const char* CLIENT_ID = "yourMQTTClientID";
const char* MQTT_USER = "yourMQTTHostUser";
const char* MQTT_PASSWORD = "yourMQTTHostPassword";

JSONVar myObject;

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50], hum[50], temp[50], dew[50];
int value = 0;
IPAddress ipAddress;

// Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)
// The pins for I2C are defined by the Wire-library.
// On an arduino UNO:       A4(SDA), A5(SCL)
// On an arduino MEGA 2560: 20(SDA), 21(SCL)
// On an arduino LEONARDO:   2(SDA),  3(SCL), ...
#define OLED_RESET     -1 // Reset pin # (or -1 if sharing Arduino reset pin)
#define SCREEN_ADDRESS 0x3C ///< See datasheet for Address; 0x3D for 128x64, 0x3C for 128x32
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  Serial.begin(9600);

  // SSD1306_SWITCHCAPVCC = generate display voltage from 3.3V internally
  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    Serial.println(F("SSD1306 allocation failed"));
    for (;;); // Don't proceed, loop forever
  }

  // clear the screen
  clearDisplay();

  // start Wifi
  setup_wifi();

  // start MQT
  client.setServer(MQTT_BROKER, 1883);

  // start DHT
  setupDHT();

}

// Clear the display at startup
void clearDisplay() {
  // Clear the buffer
  Serial.println(F("Clear display..."));
  display.clearDisplay();
  display.display();
}

// Start Wifi for MQTT
void setup_wifi() {
  delay(10);
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(SSID);

  WiFi.begin(SSID, PSK);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  ipAddress = WiFi.localIP();
  Serial.println(WiFi.localIP());
}

void setupDHT() {
  pinMode(DHTPin, INPUT);
  dht.begin();
}


void printIp() {
  display.setFont(null);
  display.setTextSize(1);             // Normal 1:1 pixel scale
  display.setTextColor(SSD1306_WHITE);        // Draw white text
  display.setCursor(0, 0);            // Start at top-left corner
  display.print("IP: "); 
  display.println(ipAddress);
  display.drawLine(0, 10, 132, 10, SSD1306_WHITE);

}

void readTempDHT() {
  humidity = dht.readHumidity();
  temperature = dht.readTemperature();

  // calibrate
  temperature--;

  dewpoint = calcDewpoint(humidity, temperature);

  Serial.println(temperature);
  Serial.println(humidity);
  Serial.println(dewpoint);


  snprintf (hum, 50, "LF   %d.%d %%", (int)humidity, (int)(humidity * 10) % 10);
  snprintf (temp, 50, "TEMP %d.%d C", (int)temperature, (int)(temperature * 10) % 10);
  snprintf (dew, 50, "TP   %d.%d C", (int)dewpoint, (int)(dewpoint * 10) % 10);

  displayTempHum(temp, hum, dew);

}

float calcDewpoint(float humi, float temp) {
  float k;
  k = log(humi / 100) + (17.62 * temp) / (243.12 + temp);
  return 243.12 * k / (17.62 - k);
}

void displayTempHum(char* t, char* h, char* d) {
  Serial.println("------------- DISPLAY");
  Serial.println(h);
  Serial.println(t);
  Serial.println(d);



  display.setFont(&FreeMono9pt7b);
  display.setTextSize(1);             // Normal 1:1 pixel scale
  display.setTextColor(SSD1306_WHITE);        // Draw white text
  display.setCursor(0, 26);

  display.println(t);
  display.println(h);
  display.println(d);

}

void connectMQT() {
  while (!client.connected()) {
    Serial.print("Reconnecting...");
    if (!client.connect(CLIENT_ID, MQTT_USER, MQTT_PASSWORD)) {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" retrying in 5 seconds");
      delay(5000);
    }
  }
}

char* string2char(String command) {
  if (command.length() != 0) {
    char *p = const_cast<char*>(command.c_str());
    return p;
  }
}

void loop() {
  display.clearDisplay();
  printIp();
  readTempDHT();
  display.display();

  if (!client.connected()) {
    connectMQT();
  }
  client.loop();

  myObject["uptime"] = millis();
  myObject["type"] = "D1 mini/DHT22/SSD1306";
  myObject["hum"] = humidity;
  myObject["temp"] = temperature;
  myObject["dew"] = dewpoint;

  char buf[100] = "";
  strcat(buf, "tele/");
  strcat(buf, CLIENT_ID);
  strcat(buf, "/SENSOR");

  Serial.println(String(buf));
  Serial.println(JSON.stringify(myObject));

  client.publish(string2char(String(buf)), string2char(JSON.stringify(myObject)));

  delay(10000);
}