Overview

The SHT31 (part of Sensirion's SHT3x series including SHT30, SHT31, and SHT35) is a high-accuracy digital humidity and temperature sensor. Built on Sensirion's CMOSens MEMS technology, it integrates a capacitive humidity sensor, a bandgap temperature sensor, an analog-to-digital converter, and signal processing circuitry on a single chip.

With outstanding precision ($\pm 0.2^\circ\text{C}$ temperature accuracy, $\pm 2\%\text{ RH}$ humidity accuracy), low power consumption, an onboard heating element to clear internal condensation, programmable threshold ALERT outputs, and dual $I^2C$ address options (0x44 / 0x45), the SHT31 is widely regarded as the gold standard environmental sensor for precision HVAC control, weather stations, laboratory datalogging, and industrial IoT nodes.

Quick reference

Pinout

Breakout modules expose a 5-pin or 6-pin 0.1" (2.54 mm) header:

Specifications

$I^2C$ Commands & CRC-8

The SHT31 uses 16-bit command codes (MSB followed by LSB):

When reading 6 measurement bytes from the sensor (2 bytes $RH$, 1 byte CRC, 2 bytes Temp, 1 byte CRC), valid data must be checked using the polynomial $X^8 + X^5 + X^4 + 1$ (0x31, init 0xFF).

Conversion Formulas

$\text{Temperature } (^\circ\text{C}) = -45 + 175 \times \left( \frac{S_T}{2^{16} - 1} \right)$

$\text{Relative Humidity (\% RH)} = 100 \times \left( \frac{S_{RH}}{2^{16} - 1} \right)$

Wiring

Example

#include <Wire.h>
#include "Adafruit_SHT31.h"

Adafruit_SHT31 sht31 = Adafruit_SHT31();

void setup() {
  Serial.begin(9600);
  while (!Serial) delay(10);

  Serial.println("Initializing SHT31 sensor...");
  // Default address 0x44
  if (!sht31.begin(0x44)) {
    Serial.println("Could not find SHT31! Check wiring.");
    while (1) delay(10);
  }
  Serial.println("SHT31 initialized.");
}

void loop() {
  float t = sht31.readTemperature();
  float h = sht31.readHumidity();

  if (!isnan(t) && !isnan(h)) {
    Serial.print("Temp: "); Serial.print(t); Serial.print(" °C | ");
    Serial.print("Humidity: "); Serial.print(h); Serial.println(" %RH");
  } else {
    Serial.println("Failed to read from SHT31");
  }

  delay(2000);
}

Common mistakes

• Leaving internal heater running continuously: The integrated heating element is intended strictly for drying out condensation in high-humidity environments. Leaving the heater turned on during normal measurements causes self-heating errors of $+3^\circ\text{C}$ to $+5^\circ\text{C}$.
• I2C address collision: Connecting multiple SHT31 sensors without pulling the ADDR pin High on the second unit results in bus collisions at address 0x44.
• Ignoring CRC bytes: Neglecting CRC validation on noisy $I^2C$ lines can lead to erroneous spike readings.

Notes

• SHT30 vs SHT31 vs SHT35: All three parts share identical pinouts and command codes. SHT30 is the budget variant ($\pm 3\% \text{ RH}$), SHT31 is standard grade ($\pm 2\% \text{ RH}$), and SHT35 is high-precision grade ($\pm 1.5\% \text{ RH}$).