Si7021 GY-21 Digital Temperature and Humidity Sensor Module – I2C

The Si7021 GY-21 Temperature and Humidity Sensor Module is a compact, high-precision digital sensor designed for accurate environmental monitoring in electronics, automation, and IoT applications.

Based on the Silicon Labs Si7021 sensor, this module combines a relative humidity sensor, temperature sensor, analog-to-digital converter, signal processing, and factory calibration in a single integrated circuit.

Featuring an I2C digital communication interface, low power consumption, and excellent long-term stability, the Si7021 is suitable for Arduino, ESP32, Raspberry Pi, and other microcontroller-based projects.

The sensor is factory-calibrated, with calibration data stored in non-volatile memory, eliminating the need for user calibration in most applications.

Key Features

• Dual Measurement: Measures relative humidity and ambient temperature.
• High Accuracy: Typical ±3% RH humidity accuracy and ±0.4°C temperature accuracy.
• Digital I2C Interface: Simple integration with microcontrollers.
• Low Power Consumption: Suitable for battery-powered monitoring applications.
• Factory Calibrated: Calibration data stored in internal non-volatile memory.
• High Resolution: Up to 12-bit humidity and 14-bit temperature resolution.
• Long-Term Stability: Designed for reliable environmental measurements.
• Compact Module: Ideal for embedded systems and IoT projects.
• Microcontroller Compatible: Supports Arduino, ESP32, Raspberry Pi, and other I2C-capable devices.

Technical Specifications

Accuracy values are typical under specified operating conditions. The module supply voltage should be verified against the exact breakout board design.

Pin Configuration

The GY-21 module typically provides four connection pins.

Connection Examples

Arduino UNO

ESP32

Raspberry Pi

Important: The Si7021 is a 3.3V-class sensor. Ensure that I2C pull-up resistors are connected to a compatible logic voltage. A 5V Arduino UNO may require an I2C level shifter, depending on the breakout board circuitry.

Applications

• Arduino and ESP32 Projects
• Raspberry Pi Environmental Monitoring
• IoT Weather Stations
• Smart Home Automation
• HVAC Monitoring Systems
• Greenhouse Monitoring
• Indoor Climate Monitoring
• Data Logging Systems
• Industrial Environmental Monitoring
• Educational Electronics Projects

Important Notes

• The Si7021 uses the I2C communication protocol.
• Its fixed I2C address is 0x40.
• The bare Si7021 sensor operates from 1.9V to 3.6V; do not assume the breakout board accepts 5V without checking its circuitry.
• Use 3.3V-compatible I2C logic unless the module provides verified level shifting.
• Avoid direct water exposure and prolonged condensation.
• The module is not waterproof.
• For accurate measurements, position the sensor away from heat-generating components.
• Factory calibration eliminates the need for routine user calibration in most applications.
• Header pins may require soldering before installation.

Package Includes

• 1 × Si7021 GY-21 Temperature and Humidity Sensor Module
• 1 × Male Header Pin Strip