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This project builds a local temperature-and-humidity monitor—not a networked weather station. It uses an Arduino UNO R4 WiFi, a DHT11 sensor, and a 0.96-inch SSD1306 OLED to refresh readings approximately every two seconds. The board has Wi-Fi hardware, but the published sketch does not connect to a router, cloud service, phone, or web server.
The original project is listed as “Arduino (UNO) EK Wi-Fi”; the intended board appears to be the Arduino UNO R4 WiFi. Do not confuse it with the separate Arduino UNO WiFi Rev2.
What you will build
The finished device measures:
- Temperature in degrees Celsius
- Relative humidity as a percentage
It shows both values on an OLED and prints them to the Arduino IDE Serial Monitor. In this context, “real-time” means periodic polling, not guaranteed real-time instrumentation: the program takes a new reading about every two seconds, and indoor temperature and humidity may change much more slowly.
It is best described as a room climate monitor or starter weather-station project. It does not measure air pressure, wind, rain, solar radiation, air quality, or forecasts.
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The source project and its original implementation are available on Hackster.io.
Parts required
| Part | Quantity | Purpose |
|---|---|---|
| Arduino UNO R4 WiFi | 1 | Microcontroller and possible future wireless connection |
| DHT11 sensor, preferably a three-pin module | 1 | Temperature and relative-humidity measurement |
| 0.96-inch 128×64 SSD1306 OLED | 1 | Local display |
| Breadboard | 1 | Temporary assembly |
| Jumper wires | As needed | Electrical connections |
| USB cable and computer | 1 each | Power, programming, and Serial Monitor output |
Check the labels and voltage requirements printed on your particular OLED module. Many modules use I²C address 0x3C, but some use 0x3D. A bare four-pin DHT11 may also need an external pull-up resistor on its data line; many three-pin breakout boards include one.
Wiring
DHT11 connections
| DHT11 pin | UNO R4 WiFi |
|---|---|
| VCC | 5V |
| GND | GND |
| DATA | D7 |
OLED I²C connections
| OLED pin | UNO R4 WiFi |
|---|---|
| VCC | 5V, if supported by your module |
| GND | GND |
| SDA | A4/SDA |
| SCL | A5/SCL |
Confirm the OLED’s actual pin labels before applying power. Some displays are SPI rather than I²C even when they look similar, and not every module has the same voltage requirements.
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Arduino IDE setup
- Install or open the Arduino IDE.
- Select Tools → Board → Arduino UNO R4 WiFi. Do not select UNO R3, UNO WiFi Rev2, or an ESP8266 board.
- Open Tools → Manage Libraries.
- Install Adafruit GFX Library.
- Install Adafruit SSD1306.
- Install DHT sensor library.
- Compile the sketch before uploading it.
- Upload it to the board, then open Tools → Serial Monitor and choose 9600 baud.
The UNO R4 WiFi combines a Renesas RA4M1 microcontroller with an ESP32-S3 wireless module. Its Wi-Fi and Bluetooth capabilities are available for later expansion, but simply selecting the board does not transmit this project’s readings. See the official board documentation.
Complete revised sketch
This version keeps the project’s wiring and sensor choices, but removes author-specific splash text, reports OLED errors, and uses millis() instead of blocking the main loop for two seconds.
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <DHT.h>
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
#define OLED_ADDRESS 0x3C
#define DHT_PIN 7
#define DHT_TYPE DHT11
Adafruit_SSD1306 display(
SCREEN_WIDTH,
SCREEN_HEIGHT,
&Wire,
OLED_RESET
);
DHT dht(DHT_PIN, DHT_TYPE);
unsigned long lastRead = 0;
const unsigned long readInterval = 2000;
void setup() {
Serial.begin(9600);
if (!display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDRESS)) {
Serial.println("OLED initialization failed.");
while (true) {
delay(1000);
}
}
display.clearDisplay();
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.println("Weather Monitor");
display.println("Starting...");
display.display();
dht.begin();
delay(2000);
}
void loop() {
if (millis() - lastRead < readInterval) {
return;
}
lastRead = millis();
float humidity = dht.readHumidity();
float temperature = dht.readTemperature();
if (isnan(humidity) || isnan(temperature)) {
Serial.println("DHT11 read failed.");
display.clearDisplay();
display.setTextSize(1);
display.setCursor(0, 0);
display.println("Sensor error");
display.println("Check DHT11 wiring");
display.display();
return;
}
Serial.print("Temperature: ");
Serial.print(temperature, 1);
Serial.println(" C");
Serial.print("Humidity: ");
Serial.print(humidity, 1);
Serial.println(" %");
display.clearDisplay();
display.setTextSize(2);
display.setCursor(0, 0);
display.print("T:");
display.print(temperature, 1);
display.println(" C");
display.setCursor(0, 32);
display.print("H:");
display.print(humidity, 1);
display.println(" %");
display.display();
}How the sketch works
Adafruit_SSD1306controls the 128×64 OLED over I²C.DHT(7, DHT11)tells the library that the sensor data line is connected to D7.dht.readHumidity()anddht.readTemperature()obtain the sensor values.isnan()rejects invalid readings instead of displaying misleading numbers.- The OLED is cleared and redrawn after every successful measurement.
- The two-second interval avoids reading the DHT11 too frequently.
The original sketch also displayed “DHT READING” and “ROHAN BARNWAL” during startup. Those messages are optional and have no effect on measurement.
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Build and test procedure
- Place the UNO R4 WiFi, DHT11 module, and OLED on the breadboard.
- Wire the DHT11 data pin to D7.
- Wire the OLED to 5V, GND, A4/SDA, and A5/SCL, observing the module’s requirements.
- Install the three libraries and select Arduino UNO R4 WiFi.
- Compile and upload the sketch.
- Open Serial Monitor at 9600 baud.
- Wait for the startup message and the first valid sensor reading.
- Confirm that the OLED shows temperature and humidity and that matching values appear in the Serial Monitor.
Do not expect visible changes every two seconds. Temperature and humidity usually change gradually, and the DHT11 is a basic sensor. Let the sensor settle before judging the readings, then compare them with a known thermometer or hygrometer if necessary.
Troubleshooting
The OLED is blank
- Check VCC and GND.
- Confirm that SDA and SCL are not reversed.
- Try changing
OLED_ADDRESSfrom0x3Cto0x3D. - Confirm that the display is I²C, SSD1306-compatible, and 128×64.
- Run an I²C scanner to discover the address.
- Test an Adafruit SSD1306 example before adding the DHT11.
“OLED initialization failed” appears
This indicates a display initialization, address, wiring, compatibility, or library problem. It is not normally caused by the DHT11. Check the display independently and verify the selected board and installed library.
DHT11 readings fail
- Verify that DATA is connected to D7.
- Check the sensor’s orientation and pin order.
- Make sure the code says
#define DHT_TYPE DHT11. - Inspect breadboard connections and the common ground.
- Add a pull-up resistor if using a bare sensor rather than a module.
- Do not reduce the reading interval excessively.
If you replace the DHT11 with a DHT22, change the type definition to #define DHT_TYPE DHT22, but verify the replacement module’s wiring and operating requirements rather than assuming it is a guaranteed drop-in substitute.
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Why the Wi-Fi label is misleading
The UNO R4 WiFi is genuinely wireless-capable, but this sketch contains no Wi-Fi initialization, credentials, router connection, HTTP request, MQTT client, web server, Arduino Cloud variables, or phone integration. Installing the board package alone will not make the readings remote.
To create a connected version, you would need to add:
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- Connection and reconnection handling
- A destination such as Arduino Cloud, an HTTP endpoint, MQTT broker, or local web server
- Authentication and sensible failure behavior when the network is unavailable
- Timestamps and a data-retention strategy
Arduino Cloud is one possible extension, but it is not required for the local OLED project. Plan limits, prices, and features can change, so check the current plans before choosing it.
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Choosing the right hardware
UNO R4 WiFi versus a classic UNO with ESP8266
The UNO R4 WiFi is the simpler starting point when you want the UNO form factor and integrated wireless hardware. A classic UNO paired with an ESP8266 can also connect to the internet, but it adds wiring, power, serial-communication, and sometimes voltage-level complications. Older ESP8266 tutorials may also depend on outdated services or libraries.
If you only need a wired OLED display and already own a classic UNO, the R4 WiFi’s wireless hardware is unnecessary. If you expect to add remote monitoring later, the R4 WiFi gives you a cleaner upgrade path.
DHT11 alternatives
- DHT11: Low-cost and easy to demonstrate, but basic.
- DHT22: A possible upgrade when you need a broader usable range or finer readings.
- AHT20: A modern digital temperature-and-humidity option.
- BME280: Adds atmospheric pressure, making the project more weather-station-like.
- Modulino Thermo: An Arduino-oriented temperature-and-humidity module documented for compatible Arduino boards; see the official documentation.
For a genuinely broader weather station, add a pressure sensor, anemometer, rain gauge, data logging, timestamps, and a properly shielded outdoor enclosure. Sensor placement matters: direct sun, rain, enclosure heat, and poor airflow can make otherwise functioning sensors produce unrepresentative readings.
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This is an excellent beginner electronics project because it teaches breadboard wiring, I²C displays, digital sensors, library installation, serial debugging, and basic error handling. It is not a meteorological instrument and it is not yet an IoT device.
For the original local monitor, buy only the UNO R4 WiFi, DHT11, OLED, breadboard, and wiring you need. Add cloud services or more advanced sensors only when remote access, pressure, logging, or outdoor measurements are actual requirements.
Quick Recap
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