How to Use SHT31: Examples, Pinouts, and Specs

The SHT31 is a high-accuracy digital humidity and temperature sensor designed and manufactured by Sensirion. It offers excellent performance and a wide range of features, making it ideal for advanced consumer products, industrial systems, and Internet of Things (IoT) applications. Its precision and reliability are well-suited for environmental monitoring, weather stations, smart home automation, and HVAC systems.

• Humidity Measurement Range: 0 to 100% RH
• Temperature Measurement Range: -40°C to +125°C
• Humidity Accuracy: ±2% RH (10 to 90% RH)
• Temperature Accuracy: ±0.3°C
• Supply Voltage Range: 2.4V to 5.5V
• Interface: I2C
• Response Time: < 8 sec (tau63%)
• I2C Address Options: 0x44 (ADDR pin connected to GND) or 0x45 (ADDR pin connected to VDD)

To use the SHT31 sensor in a circuit:

1. Connect the VDD pin to a power supply within the 2.4V to 5.5V range.
2. Connect the GND pin to the ground of the power supply.
3. Connect the SDA and SCL pins to the I2C data and clock lines, respectively.
4. Optionally, connect the nRESET pin to a digital output on your microcontroller if you wish to reset the sensor via software.
5. Optionally, use the ALERT pin for system alerts based on humidity and temperature thresholds.
6. Set the ADDR pin to either GND or VDD to select the I2C address.

• Ensure that the power supply is stable and within the specified voltage range.
• Use pull-up resistors on the SDA and SCL lines, typically 10kΩ.
• Keep the I2C lines as short as possible to prevent signal degradation.
• Avoid placing the sensor near heat sources or in direct sunlight to prevent false readings.
• Implement proper ESD precautions when handling the sensor.

#include <Wire.h>
#include "SHT31.h"

SHT31 sht31 = SHT31();

void setup() {
  Serial.begin(9600);
  Wire.begin();
  if (!sht31.begin(0x44)) { // Set to 0x45 if ADDR pin is tied to VDD
    Serial.println("Could not find a valid SHT31 sensor, check wiring!");
    while (1) delay(1);
  }
}

void loop() {
  float temp = sht31.getTemperature();
  float hum = sht31.getHumidity();

  if (!isnan(temp)) { // Check if 'temp' is not an error value
    Serial.print("Temp *C = "); Serial.println(temp);
  } else {
    Serial.println("Failed to read temperature");
  }

  if (!isnan(hum)) { // Check if 'hum' is not an error value
    Serial.print("Hum. % = "); Serial.println(hum);
  } else {
    Serial.println("Failed to read humidity");
  }

  delay(1000);
}

• Sensor not detected: Ensure wiring is correct, pull-up resistors are in place, and the correct I2C address is used in the code.
• Inaccurate readings: Verify the sensor is not exposed to heat sources or direct sunlight. Check for proper airflow around the sensor.
• Unstable readings: Ensure the power supply is stable and within the recommended voltage range.

Q: Can the SHT31 sensor be used outdoors? A: Yes, but it should be protected from direct exposure to water and sunlight.

Q: How can I extend the I2C cable length? A: Use shielded cables and lower the pull-up resistor value to maintain signal integrity.

Q: What is the purpose of the ALERT pin? A: The ALERT pin can be used to trigger an interrupt on the host microcontroller when humidity or temperature exceeds programmed limits.

Q: How do I calibrate the sensor? A: The SHT31 is factory-calibrated. However, for critical applications, you may perform additional calibration using known humidity and temperature references.

Q: Is there a sleep mode to reduce power consumption? A: Yes, the SHT31 supports a low-power mode that can be activated via I2C commands.

This documentation provides a comprehensive guide to integrating and using the SHT31 sensor in various applications. For further information, consult the manufacturer's datasheet and application notes.