Read Temperature with DHT22

TimeEstimated Time

LevelDifficulty

BeforePrerequisites

No prerequisites.

Skills You'll Learn

• Wire a DHT22 to ESP32 3.3 V, GND, and GPIO4
• Choose safe ESP32 GPIO pins for a digital sensor
• Install and use the Arduino DHT library
• Read Celsius, Fahrenheit, humidity, and heat index
• Troubleshoot NaN readings and library errors

PartsComponents Required

• 🖥ESP32 DevKit boardAny ESP32 development board with a USB data port works.
• 🌡DHT22 temperature and humidity sensor moduleA 3-pin module is easiest because it usually includes the pull-up resistor.
• 🎚10 k ohm resistorOnly required if you use a bare 4-pin DHT22 sensor without a module board.
• 🧩BreadboardHalf-size breadboard is enough.
• 🔗Jumper wiresUse short, firm male-to-male wires for stable readings.
• 🔌USB data cableCharge-only cables can power the board but cannot upload code.

Engineering Explanation

Real WorldReal-World Analogy

Wiring Diagram

Follow these steps in order. Unplug USB before you change any wires.

1. 1

   Unplug the ESP32 USB cable before wiring.

2. 2

   Place the DHT22 module on the breadboard so each pin has its own row.

3. 3

   Connect DHT22 VCC or + to ESP32 3.3 V.

4. 4

   Connect DHT22 GND or - to ESP32 GND.

5. 5

   Connect DHT22 DATA or OUT to ESP32 GPIO4.

6. 6

   If you are using a bare 4-pin DHT22, add a 10 k ohm resistor from DATA to 3.3 V.

7. 7

   Leave the unused NC pin on a bare DHT22 disconnected.

8. 8

   In Arduino IDE, install "DHT sensor library" by Adafruit and "Adafruit Unified Sensor" from Library Manager.

⌨️Arduino Code

Copy this into Arduino IDE, then click Upload.

#include "DHT.h"

// DHT22 data pin connected to ESP32 GPIO4.
#define DHTPIN 4

// Tell the library which DHT sensor model you are using.
#define DHTTYPE DHT22

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(115200);
  delay(1000);

  dht.begin();
  Serial.println("DHT22 ESP32 room sensor ready");
  Serial.println("Reading every 2 seconds...");
}

void loop() {
  float humidity = dht.readHumidity();
  float temperatureC = dht.readTemperature();
  float temperatureF = dht.readTemperature(true);

  if (isnan(humidity) || isnan(temperatureC) || isnan(temperatureF)) {
    Serial.println("Read failed. Check wiring, power, pull-up resistor, and library setup.");
    delay(2000);
    return;
  }

  float heatIndexC = dht.computeHeatIndex(temperatureC, humidity, false);

  Serial.print("Temperature: ");
  Serial.print(temperatureC, 1);
  Serial.print(" C / ");
  Serial.print(temperatureF, 1);
  Serial.print(" F  |  Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %  |  Heat index: ");
  Serial.print(heatIndexC, 1);
  Serial.println(" C");

  delay(2000);
}

CodeLine-by-line Explanation

• DHTPIN must match the GPIO you wired to the DATA pin.
• DHTTYPE tells the library this is a DHT22, not a DHT11.
• The code waits 2 seconds between reads because the DHT22 is a slow sensor.
• isnan() protects your program from printing bad values when a read fails.

MistakesCommon Mistakes

• Serial Monitor says "Read failed"

  DATA is on the wrong GPIO, the pull-up resistor is missing, or the sensor is being read too quickly.

• Code does not compile because DHT.h is missing

  The Adafruit DHT library is not installed, or the wrong library was installed.

• Values are unrealistic or stuck

  Loose jumper wires, poor breadboard contact, heat from your fingers, or airflow directly onto the sensor.

• ESP32 uploads fail after wiring the sensor

  The sensor may be connected to a boot strapping pin or a wiring mistake may pull a pin into the wrong state during reset.

• Sensor works on Arduino Uno examples but not ESP32

  Some examples use 5 V assumptions or a different pin number.

!Troubleshooting

Most ESP32 problems are wiring, power, library, or timing issues. Check these first.

• Serial Monitor says "Read failed"

  Likely cause: DATA is on the wrong GPIO, the pull-up resistor is missing, or the sensor is being read too quickly.

  Fix: Confirm DATA goes to GPIO4, use 3.3 V and GND, add a 10 k ohm pull-up for a bare sensor, and keep delay(2000).

• Code does not compile because DHT.h is missing

  Likely cause: The Adafruit DHT library is not installed, or the wrong library was installed.

  Fix: Open Arduino IDE Library Manager and install "DHT sensor library" by Adafruit plus "Adafruit Unified Sensor".

• Values are unrealistic or stuck

  Likely cause: Loose jumper wires, poor breadboard contact, heat from your fingers, or airflow directly onto the sensor.

  Fix: Reseat the wires, keep the sensor away from the warm ESP32 board, and wait a few readings for the value to settle.

• ESP32 uploads fail after wiring the sensor

  Likely cause: The sensor may be connected to a boot strapping pin or a wiring mistake may pull a pin into the wrong state during reset.

  Fix: Use GPIO4 for this beginner circuit and disconnect power before rewiring.

• Sensor works on Arduino Uno examples but not ESP32

  Likely cause: Some examples use 5 V assumptions or a different pin number.

  Fix: Use 3.3 V logic, update DHTPIN to your ESP32 GPIO number, and select an ESP32 board in Arduino IDE.

?FAQs

• Can I power the DHT22 from 5 V with an ESP32?

  Use 3.3 V when the data pin connects directly to an ESP32 GPIO. Some DHT22 modules accept 5 V power, but their data output may also be pulled up to 5 V, which is not safe for ESP32 pins.

• Why does the DHT22 sometimes return NaN?

  NaN means the library did not receive a valid reading. The usual causes are wrong pin number, missing pull-up resistor, loose jumper wires, incorrect library, or reading faster than the sensor can update.

• Is the DHT22 better than the DHT11?

  Yes for most learning projects. DHT22 has a wider measurement range and better accuracy than DHT11, although it costs slightly more and still updates slowly.

• Which ESP32 GPIO should I use for DHT22 data?

  GPIO4 is a safe beginner choice. GPIO16, GPIO17, GPIO18, GPIO19, GPIO21, GPIO22, GPIO23, GPIO25, GPIO26, and GPIO27 can also work. Avoid boot strapping pins until you understand their startup behavior.