GY-21 Digital Temperature & Humidity Sensor Module

The GY-21 is a compact, high-accuracy digital sensor module that measures both temperature and relative humidity, based on the Sensirion SHT21 or HTU21D sensor. Ideal for weather stations, environmental monitoring, and smart home applications, this module communicates over I²C for easy integration with microcontrollers like Arduino, ESP32, or Raspberry Pi.

With factory calibration, low power consumption, and a wide sensing range, the GY-21 is perfect for both hobbyist and professional projects that require reliable environmental data.

Key Features:

• Dual Sensing Capability: Measures both temperature and relative humidity in real time

• I²C Digital Interface: Simple 2-wire communication (SDA/SCL) for quick integration

• Factory Calibrated: High accuracy and stable readings with no user calibration required

• Low Power Operation: Suitable for battery-powered and low-energy applications

• Compact Design: Small PCB size makes it easy to embed in portable or space-constrained systems

Specifications:

• Sensor Type: SHT21 or HTU21D (depending on batch)

• Operating Voltage: 1.5V to 3.6V (typically 3.3V)

• Current Consumption:

  • Idle: <1 µA

  • Active (measuring): ~450 µA

• Humidity Range: 0% – 100% RH (±2% typical accuracy)

• Temperature Range: -40°C to +125°C (±0.3°C typical accuracy)

• Interface: I²C (Address: 0x40)

• Board Dimensions: Approx. 15mm x 12mm

• Response Time:

  • Humidity: 8 seconds (typical)

  • Temperature: 5 seconds (typical)

Applications:

• DIY weather stations

• Smart home and HVAC systems

• Indoor air quality monitoring

• Agricultural and greenhouse monitoring

• IoT and wireless sensor networks

Whether you’re building an IoT-enabled environmental monitor or a compact weather sensor, the GY-21 module delivers dependable temperature and humidity readings with minimal complexity.