AHT10 / AHT20 / AHT21B / AHT25 Temperature & Humidity Sensor Module — I²C, High Precision

AHT10 / AHT20 / AHT21B / AHT25 Temperature & Humidity Sensor Module — I²C, High Precision

The AHT10, AHT20, AHT21B, and AHT25 are high-precision digital temperature and humidity sensors from ASAIR (Aosong Electronics) communicating over I²C. With ±0.3°C temperature accuracy and ±2% RH humidity accuracy, they outperform the DHT22 in precision while offering the simplicity of I²C (only 2 signal wires). The module includes onboard decoupling capacitors and pull-up resistors for plug-and-play integration with Arduino, ESP32, and Raspberry Pi.

Key Specifications

Parameter	Value
Sensor IC	AHT10 / AHT20 / AHT21B / AHT25 (ASAIR)
Interface	I²C (address 0x38 fixed)
Temperature Range	-40°C – +85°C
Temperature Accuracy	±0.3°C (AHT20/AHT21B/AHT25)
Humidity Range	0% – 100% RH
Humidity Accuracy	±2% RH
Measurement Time	~75ms per reading
Supply Voltage	2.0V – 5.5V
Current Consumption	~23μA (measuring), 0.25μA (idle)

AHT Series Variant Comparison

Sensor	Temp Accuracy	Humidity Accuracy	Key Improvement
AHT10	±0.5°C	±2% RH	First generation I²C sensor
AHT20	±0.3°C	±2% RH	Improved temp accuracy, JEDEC standard
AHT21B	±0.3°C	±2% RH	AHT20 with improved calibration
AHT25	±0.3°C	±2% RH	Highest stability, industrial grade

AHT20 vs DHT22 vs BME280 — Which Sensor?

Feature	AHT20 (I²C)	DHT22 (1-wire)	BME280 (I²C/SPI)
Temp Accuracy	±0.3°C	±0.5°C	±0.5°C
Humidity	±2% RH	±2% RH	±3% RH
Pressure	No	No	Yes (±1 hPa)
Interface	I²C (2 wires)	Single-wire (1 wire)	I²C or SPI
Best for	High-accuracy temp/humidity, minimal wiring	Simple projects, single-wire	Weather station with pressure

Why Choose AHT20 / AHT21B?

• ±0.3°C accuracy — best-in-class for low-cost temperature sensors, better than DHT22
• I²C interface — only 2 signal wires (SDA + SCL), share bus with other I²C devices
• 2.0–5.5V supply — compatible with 3.3V (ESP32, STM32) and 5V (Arduino) systems
• 23μA measurement current — ultra-low power for battery-operated IoT sensors
• 75ms measurement time — fast readings for responsive environmental monitoring

Compatible With

• Arduino: Adafruit AHTX0 library — aht.getEvent(&humidity, &temp);
• ESP32 / ESP8266: Same Adafruit AHTX0 library, 3.3V compatible
• Raspberry Pi: Adafruit CircuitPython AHTx0 library
• MicroPython: ahtx0 MicroPython driver
• Home Assistant / ESPHome: aht10 or aht20 sensor platform

Frequently Asked Questions

Q: How do I read AHT20 with Arduino?
A: Install “Adafruit AHTX0” library in Arduino IDE. Connect SDA to A4 (UNO) or SDA pin, SCL to A5 or SCL pin. Code: Adafruit_AHTX0 aht; aht.begin(); sensors_event_t humidity, temp; aht.getEvent(&humidity, &temp); Serial.println(temp.temperature); Serial.println(humidity.relative_humidity);

Q: Can I use multiple AHT20 sensors on the same I²C bus?
A: AHT20 has a fixed I²C address (0x38) with no address selection pins, so only one AHT20 can be on a single I²C bus. For multiple sensors, use an I²C multiplexer (TCA9548A, 8 channels) to switch between sensors, or use different sensor types (BME280 at 0x76/0x77, SHT31 at 0x44/0x45) on the same bus.

Q: What is the difference between AHT20 and AHT21B?
A: AHT21B is an improved version of AHT20 with enhanced calibration and slightly better long-term stability. Both have identical electrical specifications (±0.3°C, ±2% RH) and I²C interface. AHT21B is the recommended version for new designs. Both are supported by the same Adafruit AHTX0 library.

Package Contents

• 1× AHT10 / AHT20 / AHT21B / AHT25 Temperature & Humidity Sensor Module (I²C)

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