SHT31 | GUILCOR SENSORS

SHT31
Temperature sensors

Digital temperature and humidity sensor with fast response and high reliability for HVAC and environmental monitoring.

Maximum precision
+/- 0,3°K

Measurement range
-40 / 125°C

Resolution
16 bits

Power supply voltage
2,4 → 5,5V

Sampling rate

1 to 10Hz

I2C adress
0 x 44

Typical current
150µA(active)

Price
Medium

What is a SHT31 sensor ?

The SHT31 is an integrated digital temperature and humidity sensor developed by Sensirion (Switzerland).

It succeeds the SHT21 and SHT15, offering improved accuracy, long-term stability, and immunity to contaminants (thanks to its optional protective coating).

It is a preferred component for all ambient measurement applications where reliability and calibration are essential.

Operating principle

The SHT31 uses two internal sensing elements:

an integrated temperature measurement diode (for compensation calculation),
a capacitive humidity sensor whose dielectric constant varies with moisture content.

These two measurements are converted into digital values via a 16-bit ADC and transmitted via I²C.

The conversion equations are standardized by Sensirion:

T(°C) = −45 + 175 × (S_T / 65535)

where S_T and S_RH are the raw values read (16 bits).

Temperature / humidity curve (Conversion examples)

Raw measurement (hex)	Temperature (°C)	Humidity (%)
0x0000	-45	0,0
0x8000	42,5	50,0
0xFFFF	130	100,0

💡 The output is linear and factory calibrated — no additional correction needed.

Principle diagram (I2C connection)

+3.3V
 │
[SHT31]
 │ SDA ─────────┐
 │ SCL ─────────┤── [I²C Microcontroller]
 │ ADDR (option)
 │ GND

💡 ADDR connected to GND → 0x44; to VCC → 0x45.

Two SHT31 sensors can coexist on the same bus.

Application areas

🌤️ Connected weather stations

🧠 IoT and home automation systems

⚙️ Climate chambers and HVAC

🧪 Environmental instrumentation

🏭 Industrial humidity/temperature monitoring

Should I choose a SHT31 sensor ?

Strengths points

🎯 High precision double measurement
→ ±0.3 K in temperature and ±2% RH, factory calibrated.
💨 Fast response time
→ Complete measurements in less than 10 ms — ideal for dynamic applications.
🧱 Compact and protected case
→ Available with PTFE coating or hydrophobic protection filter.
⚡ Stable digital calibration
→ Each sensor is individually calibrated with internal EEPROM coefficients.

Weaknesses points

🌬️ Sensitivity to deposits and contaminants
→ Without protection, the sensor can drift in dusty or oily environments.
📡 Interface only I²C
→ No SPI version, some industrial applications prefer the differential bus.
💸 Cost higher than a simple temperature sensor
→ But justified by the dual measurement and the reliability of Sensirion.

Useful information

Here is some useful information regarding the SHT31 sensors.

Main I²C Commands

Command (hex)	Mode	Description
0x2400	High repeatability, no clock stretching	Complete measurement (T + RH)
0x240B	Medium repeatability	Less precise, faster
0x2416	Low repeatability	For energy savings
0xE000	Read status register	State reading
0x30A2	Soft reset	Software reset

I²C Reading Example (pseudo-code)

i2c_start();
i2c_write(0x44 << 1);
i2c_write(0x24);
i2c_write(0x00);
delay(15); // Waiting for conversion
i2c_start();
i2c_write((0x44 << 1) | 1);
MSB_T = i2c_read_ack();
LSB_T = i2c_read_ack();
CRC_T = i2c_read_ack();
MSB_RH = i2c_read_ack();
LSB_RH = i2c_read_ack();
CRC_RH = i2c_read_nack();
i2c_stop();

S_T = (MSB_T << 8) | LSB_T;
S_RH = (MSB_RH << 8) | LSB_RH;
temp = -45 + (175.0 * S_T / 65535.0);
rh = 100.0 * S_RH / 65535.0;

✅ Example:

S_T = 29,000 → T = 31.6 °C

S_RH = 36,000 → RH = 54.9 %

Typical integration diagram

3.3V ───────────┐ │ [SHT31] │ SDA ───────┐ │ SCL ───────┤── MCU (Arduino, ESP32, STM32…) │ GND

💡 Provide pull-up resistors of 10 kΩ if not included on the module.

State register bits (read 0xE000)