Read a DHT22 on an ESP32-C3 and Print to Serial

The DHT22 reads air temperature and humidity over a single wire, and the ESP32-C3 is a small, fast board that runs on 3.3 volts. Together they make a good first sensor project. In this post you will wire a DHT22 to an ESP32-C3 in your browser, choose a GPIO that is safe to use, and print readings to the serial monitor at 115200 baud. If you have already read the Arduino Uno version of this project, you will find the sketch almost the same. The differences are in the wiring.

Choosing a GPIO on the C3

On an Uno you pick a pin number and go. On the ESP32-C3 it pays to look first, because several pins have a job.

Mokxi's ESP32-C3 board is the DevKitM-1. Its usable pins are GPIO 0 to 10 and 18 to 21. A few of those come with baggage:

• GPIO 8 carries the on-board LED, which is why LED_BUILTIN is 8.
• GPIO 9 is the BOOT button. Pressing it pulls the pin low.
• GPIO 18 and 19 are the USB pins on the real board, and 20 and 21 are UART0. Mokxi treats them as plain GPIO and sends serial text to the monitor instead, but on real hardware you would rather leave all four alone.

That leaves several free pins, among them 4, 5, 6, 7 and 10. I used GPIO 4. It has no special job for a digital sensor, and it is the pin Mokxi's smart home example for the C3 uses for its DHT22.

Power it from 3.3 volts

The C3 is a 3.3 volt board: its pins drive 3.3 volts or 0 volts, and the input threshold is 1.65 volts. The DHT22 accepts a supply from 3.3 volts up, so power it from the board's 3V3 pin. That keeps the data wire at a level the C3 expects. On the Uno post we used 5 volts, which would be the wrong choice here.

What you need

• An ESP32-C3 (the DevKitM-1)
• A DHT22 sensor
• Three jumper wires

No resistor is needed. The three-pin DHT22 module carries the pull-up resistor on its data line, and Mokxi's part models it with a pullup property that is on by default.

Wire it up

DHT22 pin	C3 pin	What it does
VCC	3V3	Power, at the board's own voltage.
DATA	GPIO 4	One wire that carries both readings.
GND	GND	Ground.

The complete sketch

#include <DHT.h>

const int DHT_PIN = 4;  // GPIO4: a plain input/output pin on the ESP32-C3

DHT dht(DHT_PIN, DHT22);

void setup() {
  Serial.begin(115200);
  dht.begin();
  Serial.println("DHT22 on GPIO4, ESP32-C3");
}

void loop() {
  delay(2000);  // the DHT22 makes a new reading about every two seconds

  float humidity = dht.readHumidity();
  float celsius = dht.readTemperature();

  if (isnan(humidity) || isnan(celsius)) {
    Serial.println("Read failed (NaN). Check the DATA wire and the 3V3 power.");
    return;
  }

  float fahrenheit = celsius * 9.0 / 5.0 + 32.0;

  Serial.print("Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %   Temperature: ");
  Serial.print(celsius, 1);
  Serial.print(" C (");
  Serial.print(fahrenheit, 1);
  Serial.println(" F)");
}

I compiled this sketch for the ESP32-C3 with Mokxi's own build path and ran it in the simulator on this wiring.

Line by line

• #include <DHT.h> brings in the DHT library. In Mokxi it is built in under its usual name, so the line compiles as it stands.
• const int DHT_PIN = 4; names the pin once. On the C3 this number is the GPIO number.
• DHT dht(DHT_PIN, DHT22); makes the sensor object. Use DHT11 as the second argument for the blue sensor.
• Serial.begin(115200); opens the serial monitor at 115200 baud, the speed ESP32 sketches usually use. The Uno post used 9600.
• dht.begin(); gets the sensor ready.
• delay(2000); waits two seconds. A DHT22 makes a new reading about every two seconds, so asking sooner gains nothing.
• readHumidity() and readTemperature() each return a float. Temperature is in Celsius unless you pass true.
• isnan(...) checks for "not a number", which is how the library reports a failed read. Printing a message and then returning skips the rest of that pass through loop().
• celsius * 9.0 / 5.0 + 32.0 converts to Fahrenheit.
• The Serial.print lines build one tidy line. The 1 in print(humidity, 1) means one digit after the decimal point.

What you should see

Press Run and open the serial monitor. With the part's defaults, which are 22 degrees Celsius and 50 percent humidity, a new line arrives every two seconds:

Humidity: 50.0 %   Temperature: 22.0 C (71.6 F)

Click the sensor on the canvas. It has two sliders, one for temperature and one for humidity. In a real room you cannot slide the weather, but here the slider is the world, so you can test your code at any value. Move one and the next line follows.

Uno and C3, side by side

	Uno post	This post
Supply	5V	3V3
Data pin	2	GPIO 4
Serial speed	9600	115200
Sketch	Same DHT calls	Same DHT calls

That is the whole difference. The library hides the sensor's one-wire timing, so the same calls work on both boards. What changes is how you wire it and which pin you pick. If you see NaN, the Uno post lists the three usual causes: a missing pull-up, reading too soon after power-up, and a loose or wrong data wire.

Try next

1. Change DHT22 to DHT11 and set the part's model property to match.
2. Light the on-board LED on GPIO 8 when humidity goes above a number you choose.
3. Print only when the reading changes by half a degree.
4. Move the data wire to GPIO 5 and change DHT_PIN to match.
5. Read the Arduino DHT22 guide for another wiring and a longer walkthrough.

Try it on Mokxi

Open the DHT sensor part page for the pins and the ESP32-C3 board page for the header and what the model includes. The ESP32 simulator is where you can build this circuit.

Ready to build it yourself? Create your free Mokxi account and open the editor in your browser. No installs, no parts to buy.