7Semi STS4x Arduino Library

Arduino driver for the Sensirion STS4x digital temperature sensors.

The STS4x series are high-accuracy digital temperature sensors with fast response time and low power consumption. These sensors support I²C communication and are ideal for applications such as:

• Environmental monitoring
• HVAC systems
• Industrial sensing
• IoT devices

This library provides a clean and efficient interface for:

• Temperature (°C) reading
• CRC-validated data communication
• Configurable measurement precision (repeatability)
• Optional smoothing filter

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Features

• Temperature measurement (°C)
• Supports STS40 / STS41 / STS45
• High, medium, and low precision modes
• CRC validation for reliable data
• Optional smoothing (EMA filter)
• Soft reset support
• Serial number reading
• Lightweight and fast implementation
• ESP32 compatible

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Supported Platforms

• Arduino UNO / Mega
• ESP32
• Any board supporting Wire (I²C)

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Hardware

Supported Sensors

7Semi Temperature Sensor Breakouts:

• STS40
• STS41
• STS45

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Connection

The sensor uses I²C communication.

I²C Wiring

Sensor Pin	MCU Pin	Description
VCC	3.3V / 5V	Sensor power
GND	GND	Ground
SDA	SDA	I²C data
SCL	SCL	I²C clock

I²C Notes

• Default address: 0x44
• Recommended speed: 100kHz – 400kHz

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Installation

Arduino Library Manager

1. Open Arduino IDE
2. Go to Library Manager
3. Search for 7Semi STS4x
4. Click Install

Manual Installation

1. Download repository as ZIP
2. Go to Sketch → Include Library → Add .ZIP Library

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Example

#include <7Semi_STS4x.h>

STS4x_7Semi sensor;

void setup()
{
    Serial.begin(115200);

    if(!sensor.begin())
    {
        Serial.println("Sensor not detected");
        while(1);
    }
}

void loop()
{
    float temperature;

    if(sensor.readTemperature(temperature))
    {
        Serial.print("Temperature: ");
        Serial.print(temperature);
        Serial.println(" °C");
    }
    else
    {
        Serial.println("Read failed!");
    }

    delay(100);
}

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Library Overview

Reading Temperature

float temperature;
sensor.readTemperature(temperature);

Serial.print("Temperature: ");
Serial.println(temperature);

Returns the measured temperature in degrees Celsius.

Quick Read (Single Line)

Serial.print("Temperature: ");
Serial.println(sensor.readTemperature(),2);

Sensor Configuration

sensor.readTemperature(temp, PRECISION_HIGH);

Parameters:

• Precision – Measurement precision level

Precision options:

PRECISION_LOW
PRECISION_MEDIUM
PRECISION_HIGH

Enable Smoothing

sensor.enableSmooth(true, 0.1f);

Applies exponential moving average filter.

Read Serial Number

uint64_t serial;
sensor.readSerialNumber(serial);

Returns unique sensor ID.

Sensor Reset

sensor.softReset();

Resets internal sensor state.

Example Applications

Typical applications include:

• Environmental monitoring

• HVAC systems

• IoT temperature sensing

• Data logging systems

• Industrial monitoring

• Smart home monitoring

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License

MIT License

Author

7Semi