How to Use AHT25: Examples, Pinouts, and Specs

The AHT25 is a digital temperature and humidity sensor manufactured by ASAIR (AOSONG). It is designed to provide accurate and reliable measurements of environmental conditions, making it ideal for a wide range of applications. The sensor features a built-in I2C interface, which simplifies integration with microcontrollers and other digital systems. With its high precision, low power consumption, and compact design, the AHT25 is well-suited for use in consumer electronics, HVAC systems, weather monitoring, and industrial automation.

• Smart home devices (e.g., thermostats, air purifiers)
• Weather stations and environmental monitoring
• Industrial process control
• HVAC systems for temperature and humidity regulation
• IoT (Internet of Things) applications

The AHT25 sensor offers the following key technical specifications:

The AHT25 has four pins, as described in the table below:

1. Power Supply: Connect the VDD pin to a 3.3V or 5V power source and the GND pin to ground.
2. I2C Communication: Connect the SDA and SCL pins to the corresponding I2C pins on your microcontroller. Use pull-up resistors (typically 4.7kΩ) on both SDA and SCL lines if not already provided by your microcontroller.
3. Initialization: Initialize the I2C interface on your microcontroller and configure the AHT25 for data acquisition.
4. Data Reading: Send the appropriate I2C commands to read temperature and humidity data from the sensor.

• Power Stability: Ensure a stable power supply to avoid measurement errors.
• Placement: Avoid placing the sensor in areas with high airflow or direct exposure to water droplets, as this may affect accuracy.
• I2C Address: The default I2C address of the AHT25 is 0x38. Ensure no address conflicts if multiple I2C devices are used.
• Warm-Up Time: Allow the sensor to stabilize for at least 20ms after power-up before taking measurements.

Below is an example of how to interface the AHT25 with an Arduino UNO using the I2C protocol:

#include <Wire.h>

// AHT25 I2C address
#define AHT25_ADDRESS 0x38

void setup() {
  Wire.begin(); // Initialize I2C communication
  Serial.begin(9600); // Initialize serial communication for debugging

  // Initialize the AHT25 sensor
  Wire.beginTransmission(AHT25_ADDRESS);
  Wire.write(0xE1); // Send initialization command
  Wire.endTransmission();
  delay(20); // Wait for sensor to stabilize
}

void loop() {
  // Request data from the AHT25 sensor
  Wire.beginTransmission(AHT25_ADDRESS);
  Wire.write(0xAC); // Trigger measurement command
  Wire.write(0x33); // Data byte 1
  Wire.write(0x00); // Data byte 2
  Wire.endTransmission();
  delay(80); // Wait for measurement to complete

  // Read 6 bytes of data from the sensor
  Wire.requestFrom(AHT25_ADDRESS, 6);
  if (Wire.available() == 6) {
    uint8_t data[6];
    for (int i = 0; i < 6; i++) {
      data[i] = Wire.read();
    }

    // Process temperature and humidity data
    uint32_t humidity = ((uint32_t)data[1] << 12) | ((uint32_t)data[2] << 4) | (data[3] >> 4);
    uint32_t temperature = ((uint32_t)(data[3] & 0x0F) << 16) | ((uint32_t)data[4] << 8) | data[5];

    float humidityPercent = (humidity * 100.0) / 1048576.0; // Convert to percentage
    float temperatureCelsius = (temperature * 200.0 / 1048576.0) - 50.0; // Convert to Celsius

    // Print results to the serial monitor
    Serial.print("Humidity: ");
    Serial.print(humidityPercent);
    Serial.println(" %");
    Serial.print("Temperature: ");
    Serial.print(temperatureCelsius);
    Serial.println(" °C");
  }

  delay(2000); // Wait 2 seconds before the next reading
}

1. No Data from Sensor:

   • Cause: Incorrect I2C wiring or address mismatch.
   • Solution: Verify the SDA and SCL connections and ensure the I2C address is set to 0x38.

2. Inaccurate Readings:

   • Cause: Sensor placement in an unstable environment (e.g., high airflow).
   • Solution: Place the sensor in a stable environment and ensure proper ventilation.

3. Initialization Failure:

   • Cause: Insufficient warm-up time or incorrect initialization sequence.
   • Solution: Allow at least 20ms for the sensor to stabilize after power-up and verify the initialization commands.

• Q: Can the AHT25 operate at 5V?

  • A: Yes, the AHT25 supports a supply voltage range of 2.0V to 5.5V.

• Q: Do I need external pull-up resistors for I2C?

  • A: Yes, if your microcontroller does not have built-in pull-up resistors, you need to add external ones (typically 4.7kΩ).

• Q: How often can I take measurements?

  • A: The AHT25 has a response time of ≤8 seconds, but for most applications, a 2-second interval is sufficient.

This concludes the documentation for the AHT25 sensor.