ESP32 SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor

Code Examples

Below you can find code examples of SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor with ESP32 in several frameworks:

• Arduino IDE
• ESP-IDF
• ESPHome
• PlatformIO
• MicroPython

ESP32 SHT21 / HTU21 / GY-21 / SI7021 Arduino IDE Code Example

Example in Arduino IDE

Fill in your main Arduino IDE sketch file with the following code to use the SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor:

#include <Wire.h>
#include "SHT21.h"

SHT21 sht;

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

void loop() {
  float temperature = sht.getTemperature();
  float humidity = sht.getHumidity();
  Serial.print("Temperature: ");
  Serial.print(temperature);
  Serial.println(" °C");
  Serial.print("Humidity: ");
  Serial.print(humidity);
  Serial.println(" %");
  delay(2000);
}

This Arduino sketch demonstrates how to interface with these sensors using the SHT21 library. It initializes the sensor and reads temperature and humidity data every 2 seconds, printing the results to the Serial Monitor. Ensure that the SHT21 library is installed in your Arduino IDE.

Connect your ESP32 to your computer via a USB cable, Ensure the correct Board and Port are selected under Tools, Click the "Upload" button in the Arduino IDE to compile and upload the code to your ESP32.

ESP32 SHT21 / HTU21 / GY-21 / SI7021 ESP-IDF Code Example

Example in Espressif IoT Framework (ESP-IDF)

If you're using ESP-IDF to work with the SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor, here's how you can set it up and read data from the sensor. Fill in this code in the main ESP-IDF file:

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/i2c.h"

#define I2C_MASTER_SCL_IO    22    /*!< GPIO number used for I2C master clock */
#define I2C_MASTER_SDA_IO    21    /*!< GPIO number used for I2C master data */
#define I2C_MASTER_NUM       I2C_NUM_0 /*!< I2C master I2C port number */
#define I2C_MASTER_FREQ_HZ   100000     /*!< I2C master clock frequency */
#define SHT21_SENSOR_ADDR    0x40       /*!< I2C address */

void read_sensor() {
    uint8_t data[3];
    uint8_t cmd = 0xF5; // Humidity command
    i2c_master_write_to_device(I2C_MASTER_NUM, SHT21_SENSOR_ADDR, &cmd, 1, pdMS_TO_TICKS(1000));
    vTaskDelay(pdMS_TO_TICKS(50));
    i2c_master_read_from_device(I2C_MASTER_NUM, SHT21_SENSOR_ADDR, data, 3, pdMS_TO_TICKS(1000));

    uint16_t raw_humidity = (data[0] << 8) | (data[1] & 0xFC);
    float humidity = -6.0 + 125.0 * (raw_humidity / 65536.0);

    cmd = 0xF3; // Temperature command
    i2c_master_write_to_device(I2C_MASTER_NUM, SHT21_SENSOR_ADDR, &cmd, 1, pdMS_TO_TICKS(1000));
    vTaskDelay(pdMS_TO_TICKS(50));
    i2c_master_read_from_device(I2C_MASTER_NUM, SHT21_SENSOR_ADDR, data, 3, pdMS_TO_TICKS(1000));

    uint16_t raw_temperature = (data[0] << 8) | (data[1] & 0xFC);
    float temperature = -46.85 + 175.72 * (raw_temperature / 65536.0);

    printf("Temperature: %.2f °C\n", temperature);
    printf("Humidity: %.2f %%\n", humidity);
}

void app_main() {
    // Initialize I2C
    i2c_config_t conf = {
        .mode = I2C_MODE_MASTER,
        .sda_io_num = I2C_MASTER_SDA_IO,
        .scl_io_num = I2C_MASTER_SCL_IO,
        .sda_pullup_en = GPIO_PULLUP_ENABLE,
        .scl_pullup_en = GPIO_PULLUP_ENABLE,
        .master.clk_speed = I2C_MASTER_FREQ_HZ,
    };
    i2c_param_config(I2C_MASTER_NUM, &conf);
    i2c_driver_install(I2C_MASTER_NUM, conf.mode, 0, 0, 0);

    while (1) {
        read_sensor();
        vTaskDelay(pdMS_TO_TICKS(2000));
    }
}

This ESP-IDF code demonstrates how to read temperature and humidity data from the SHT21-compatible sensors. It sends commands to initiate measurements, retrieves the raw data over I2C, and calculates the actual values based on datasheet formulas. Results are printed to the console every 2 seconds.

Update the I2C pins (I2C_MASTER_SDA_IO and I2C_MASTER_SCL_IO) to match your ESP32 hardware setup, Use idf.py build to compile the project, Use idf.py flash to upload the code to your ESP32.

ESP32 SHT21 / HTU21 / GY-21 / SI7021 ESPHome Code Example

Example in ESPHome (Home Assistant)

Fill in this configuration in your ESPHome YAML configuration file (example.yml) to integrate the SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor

sensor:
  - platform: sht3x
    address: 0x40
    temperature:
      name: "Room Temperature"
    humidity:
      name: "Room Humidity"
    update_interval: 60s

This ESPHome configuration uses the `sht3x` platform for SHT21-compatible sensors. It defines two sensor entities for temperature and humidity, with human-readable names. The `update_interval` is set to 60 seconds, ensuring periodic updates of the readings.

Upload this code to your ESP32 using the ESPHome dashboard or the esphome run command.

ESP32 SHT21 / HTU21 / GY-21 / SI7021 PlatformIO Code Example

Example in PlatformIO Framework

For PlatformIO, make sure to configure the platformio.ini file with the appropriate environment and libraries, and then proceed with the code.

Configure platformio.ini

First, your platformio.ini should look like below. You might need to include some libraries as shown. Make sure to change the board to your ESP32:

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
lib_deps = 
    DFRobot/SHT21 @ ^1.0.0
monitor_speed = 115200

ESP32 SHT21 / HTU21 / GY-21 / SI7021 PlatformIO Example Code

Write this code in your PlatformIO project under the src/main.cpp file to use the SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor:

#include <Wire.h>
#include "SHT21.h"

SHT21 sht;

void setup() {
    Wire.begin();
    Serial.begin(115200);
    Serial.println("SHT21 Sensor Example");
}

void loop() {
    float temperature = sht.getTemperature();
    float humidity = sht.getHumidity();

    if (!isnan(temperature) && !isnan(humidity)) {
        Serial.print("Temperature: ");
        Serial.print(temperature);
        Serial.println(" °C");

        Serial.print("Humidity: ");
        Serial.print(humidity);
        Serial.println(" %");
    } else {
        Serial.println("Failed to read from sensor");
    }

    delay(2000);
}

This PlatformIO example uses the DFRobot SHT21 library to interact with the sensor. It reads temperature and humidity every 2 seconds and prints the values to the Serial Monitor, ensuring easy integration with ESP32 and other Arduino-compatible boards.

Upload the code to your ESP32 using the PlatformIO "Upload" button in your IDE or the pio run --target upload command.

ESP32 SHT21 / HTU21 / GY-21 / SI7021 MicroPython Code Example

Example in Micro Python Framework

Fill in this script in your MicroPython main.py file (main.py) to integrate the SHT21 / HTU21 / GY-21 / SI7021 Temperature and Humidity Sensor with your ESP32.

from machine import Pin, I2C
from time import sleep

SENSOR_ADDR = 0x40
CMD_TEMP = 0xF3
CMD_HUM = 0xF5

def read_sensor(i2c, cmd):
    i2c.writeto(SENSOR_ADDR, bytearray([cmd]))
    sleep(0.05)
    data = i2c.readfrom(SENSOR_ADDR, 3)
    return (data[0] << 8 | data[1]) & 0xFFFC

def calc_temperature(raw_temp):
    return -46.85 + 175.72 * (raw_temp / 65536.0)

def calc_humidity(raw_hum):
    return -6.0 + 125.0 * (raw_hum / 65536.0)

i2c = I2C(0, scl=Pin(22), sda=Pin(21))

while True:
    raw_temp = read_sensor(i2c, CMD_TEMP)
    raw_hum = read_sensor(i2c, CMD_HUM)

    temperature = calc_temperature(raw_temp)
    humidity = calc_humidity(raw_hum)

    print("Temperature: {:.2f} °C".format(temperature))
    print("Humidity: {:.2f} %".format(humidity))
    sleep(2)

This MicroPython script interfaces with SHT21-compatible sensors over I2C. It retrieves raw temperature and humidity data, processes it using datasheet equations, and displays the results on the console every 2 seconds.

Upload this code to your ESP32 using a MicroPython-compatible IDE, such as Thonny, uPyCraft, or tools like ampy.