ESP32 UNO - DHT11 - LCD
Want a desk gadget that tells you how warm and how damp your room is? Build an ESP32 Uno DHT11 LCD meter: the sensor measures the air, and a 16x2 LCD I2C screen shows both numbers without a computer. The ESP32 Uno form board refreshes the display every 2 seconds, so a warm hand or an open window shows up on the screen almost at once.
What you will do:
- Hook up a DHT11 temperature humidity module plus a 16x2 I2C screen on the ESP32 Uno
- Install two libraries from the Arduino IDE Library Manager: Adafruit DHT and DIYables_LCD_I2C
- Get °C and % values with readTemperature() and readHumidity()
- Print both lines on the LCD screen, with a real degree symbol
Components You Need
Or you can buy the following kits:
| 1 | × | DIYables Sensor Kit (18 sensors/displays) |
Additionally, some of these links are for products from our own brand, DIYables .
Buy Note: Most LCD I2C displays available on the market are 5V displays. They may work with this board, but it is unsafe and can damage the board. We strongly recommend using the 3.3V LCD I2C display recommended above.
The Two Modules in Short
After this part, you know which job each module does in the build.
| Module | Job In This Project | Bus or Signal | Supply |
|---|---|---|---|
| DHT11 module | Measures temperature and humidity | One-wire style data on one pin | 3.3V to 5V |
| LCD I2C 16x2 | Shows two lines of 16 characters | I2C (SDA and SCL) | 5V |
The DHT11 covers 0 to 50°C (about ±2°C) and 20 to 90% humidity (about ±5%). It gives a new reading about once per second, so the 2 second loop delay suits it well.
Need the full pinout, the basic sketch or the library details of each part? Go through these guides first:
ESP32 Uno Pinout
The labels printed on the headers (D2, SDA, SCL) are not the numbers you type in a sketch. Find D2 and the SDA/SCL pins on the picture below to see their GPIO numbers before you plug in any jumper.
How to Connect
When you finish this step, the sensor data line sits on D2 and the screen sits on the I2C header.
This image is created using Fritzing. Click to enlarge image
※ NOTE THAT:
The wiring diagram may not show the correct wiring for the ESP32 Uno. The LCD backpack pulls SDA and SCL up to 5V, but ESP32 Uno pins are 3.3V only. The picture shows the LCD wired straight to SDA and SCL. We suggest a level converter between the LCD and the board, as the hardware list shows. We will update the diagram soon. Until then, follow the wiring table and the text on this page, not the picture.
Step 1 — DHT11 module
| DHT11 Pin | ESP32 Uno Pin |
|---|---|
| VCC (+) | 3.3V |
| GND (-) | GND |
| DATA (OUT) | D2 (GPIO26) |
Step 2 — LCD I2C display
| LCD Pin | ESP32 Uno Pin |
|---|---|
| VCC | 5V |
| GND | GND |
| SDA | SDA (GPIO21) |
| SCL | SCL (GPIO22) |
Good to know: the DHT11 module has its own pull-up resistor on DATA. A bare 4-pin DHT11 needs an extra 10 kΩ resistor from DATA to 3.3V.
Good to know: A4 and A5 on this board are input-only analog pins, not I2C. The LCD must go to the separate SDA and SCL header pins.
WARNING
ESP32 Uno pins use 3.3V logic and are NOT 5V tolerant. Feed the DHT11 from 3.3V, so its DATA line never rises above 3.3V. The LCD backpack runs from 5V, and many backpacks pull SDA and SCL up to that 5V. For long-term use, put a bidirectional 3.3V/5V level shifter on the two I2C lines, or take off the pull-up resistors on the backpack so the lines idle at 3.3V.
ESP32 Uno Code
This sketch reads the DHT11 on GPIO26 every 2 seconds and writes temperature on line 1 and humidity on line 2 of the LCD.
※ NOTE THAT:
LCD I2C modules from different makers can use different addresses. This sketch uses 0x27, the address of the DIYables LCD. A blank screen with a lit backlight often means a different address, such as 0x3F.
Upload and Test
- First time with this board? Set it up with ESP32 Uno - Getting Started before you continue.
- Build the circuit by following the wiring table above.
- Plug in the USB Type-C cable between the ESP32 Uno and your computer.
- Select the board in Arduino IDE: pick ESP32 Dev Module and the COM port of the board (CH340).
- Open the Library Manager with the Libraries icon in the left bar of Arduino IDE.
- Get the sensor library: type "DHT", pick the DHT sensor library from Adafruit, then press Install.
- Search for DHT sensor library created by Adafruit and click the Install button.
- Accept the extra libraries: the IDE lists some dependencies, so add them too with the Install All button.
- Search for Adafruit Unified Sensor created by Adafruit
- Get the screen library: type "DIYables LCD I2C", pick DIYables_LCD_I2C by DIYables, then press Install.
- Search for DIYables LCD I2C created by DIYables.io and click the Install button.
- Paste the sketch into a new Arduino IDE window.
- Click Upload (Upload button) and wait for "Done uploading".
- Change the air around the sensor: breathe on it gently, or put it near a cup of warm tea.
- Read the screen: you should see lines like these, and the numbers move after a few seconds.
| LCD Line | Example Text | |
|---|---|---|
| Line 1 | Temp | 26.00°C |
| Line 2 | Humi | 57.00% |
| Line 1 after breathing on it | Temp | 27.00°C |
| Line 2 after breathing on it | Humi | 71.00% |
- Pro tip: humidity jumps faster than temperature when you breathe on the DHT11. Use that as a quick check that the sensor is alive before you trust the °C value.
Blank LCD? Go to the LCD I2C troubleshooting part.
Video Tutorial
See the ESP32 Uno build in action in the video below.
Code Explanation
By the end of this part, you can change any line of the sketch with confidence.
| Code Part | What It Does |
|---|---|
| #define DHT11_PIN 26 | Sets D2 (GPIO26) as the DHT11 data pin |
| DIYables_LCD_I2C lcd(0x27, 16, 2) | Creates the screen object with address 0x27 and a 16x2 size |
| dht11.begin() and lcd.init() | Start the sensor and the screen once at power-up |
| readHumidity() and readTemperature() | Return humidity in % and temperature in °C as float values |
| isnan(...) check | Shows "Failed" when the sensor sends no valid data |
| lcd.print((char)223) | Draws the ° sign from the LCD character set |
The result is a screen that is cleared and redrawn every 2 seconds with fresh numbers.
ESP32 Uno vs UNO R4 for This Project
This table lists what is different when you move this build from the UNO R4 to the ESP32 Uno.
| Item | Arduino UNO R4 | ESP32 Uno |
|---|---|---|
| Logic voltage | 5V | 3.3V |
| DHT11 data pin in code | 2 (D2) | 26 (D2 header pin) |
| LCD I2C pins | SDA and SCL (also A4 and A5) | SDA GPIO21 and SCL GPIO22 only |
| DHT11 supply | 5V or 3.3V | 3.3V recommended |
| Libraries | DHT sensor library and DIYables_LCD_I2C | Same libraries, no change |
| WiFi and Bluetooth | WiFi on R4 WiFi only | WiFi plus Bluetooth Classic and BLE |
| Arduino IDE board | Arduino UNO R4 WiFi or Minima | ESP32 Dev Module |
The same wiring positions work as-is. Only the pin number in code changes, and you should watch the 5V pull-ups on the LCD I2C lines.
Go Wireless: Check the Room From Your Phone
After this part, you have an idea for reading the climate without walking to the LCD.
The ESP32 Uno has WiFi and Bluetooth built in. Keep the LCD for people in the room, and send the same two values to a phone or a browser too. A live chart also shows how humidity rises when you cook or take a shower.
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No COM port appears in Arduino IDE | CH340 driver missing or a charge-only USB cable | Install the CH340 driver and use a USB cable that carries data |
| Upload stops at "Failed to connect" or "Waiting for download" | The board did not enter download mode | Hold the BOOT button when the IDE starts uploading, then let go |
| Backlight lit but no characters | I2C address is not 0x27, or contrast is too low | Run an I2C scanner sketch, put the found address in the code, and turn the blue contrast screw |
| Screen completely dark | LCD has no 5V, or its wires sit on A4 and A5 | Give the LCD 5V and move SDA and SCL to GPIO21 and GPIO22 |
| "Failed" on line 1 | No valid data from the DHT11 | Check DATA on D2 (GPIO26), the 3.3V and GND wires, and the pull-up on a bare sensor |
| Sketch will not compile, DHT.h not found | Library not installed | Install DHT sensor library and Adafruit Unified Sensor from the Library Manager |
| Random characters or a frozen screen | Loose I2C jumper or long wires | Push the SDA and SCL jumpers in firmly and keep them short |
| Temperature is a few degrees too high | Heat from the board or the LCD reaches the sensor | Move the DHT11 a few centimeters away from the board and the backpack |
FAQ
How accurate is a DHT11 for a room display?
It is fine for a rough room reading. Expect about ±2°C on temperature and about ±5% on humidity. For better numbers, use a DHT22 with the same wiring idea.
Can the DHT11 run from the 5V pin of the ESP32 Uno?
It can run from 5V, but then the module pull-up lifts DATA to 5V. ESP32 Uno pins are not 5V tolerant, so 3.3V is the safe supply for this project.
Where do SDA and SCL connect on the ESP32 Uno?
Use the two pins marked SDA (GPIO21) and SCL (GPIO22) next to AREF. On this board A4 and A5 are input-only analog pins with no I2C function. Wire.begin() picks GPIO21 and GPIO22 by default, so no extra code is needed.
Do I need a level shifter between the LCD and the ESP32 Uno?
Often yes, because the backpack resistors tie the two I2C lines to its 5V supply. A cheap bidirectional level shifter keeps those lines at 3.3V on the board side. Removing the pull-up resistors on the backpack also works, because the I2C lines then idle at a safe level.
How do I display Fahrenheit instead of Celsius?
Call dht11.readTemperature(true), which returns °F. Then print "F" in place of "C" on line 1.
Which other pins can read the DHT11 on the ESP32 Uno?
Most digital header pins work, for example D3 (GPIO25) or D7 (GPIO14). Write the GPIO number in DHT11_PIN, not the D label. Skip A2 to A5 if you need the internal pull-up, and avoid D8 (GPIO12), D10 (GPIO5) and A0 (GPIO2), which are boot strapping pins.
Is the ESP32 Uno code different from the UNO R4 code here?
Only one line changes. The UNO R4 uses pin 2 for DHT11 DATA, while the ESP32 Uno uses 26, which is the same D2 header position. Both libraries work on both boards.
Why does Arduino IDE ask me to install a CH340 driver?
The ESP32 Uno uses a CH340 USB-to-serial chip for upload and Serial Monitor. Windows and macOS may need its driver before the COM port appears.
Can I fit a second DHT11 or a DHT22 in this build?
Yes. Give the second sensor its own data pin and create a second DHT object with its pin and type. Then show its values on the same LCD, or switch between the two sensors every few seconds.
What if this climate display needs more pins than the Uno headers give?
The ESP32 Uno has a few extra holes near the power header. GPIO32 and GPIO33 offer I/O, PWM and analog on ADC1, so they still read analog values while WiFi is on. GPIO15 offers I/O, PWM and analog on ADC2. Solder pin headers there and write the GPIO number in code. GPIO32 or GPIO33 are a good spot for a second DHT11 or a button. Two warnings: GPIO15 and GPIO0 (the IO0 pin at the unused Uno NC spot) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code, so pick GPIO32/33 first. Never use the six holes under the digital header (SD0 to SD3, CMD, CLK = GPIO6 to GPIO11), because they connect to the flash chip and using them crashes the board.