AHT20 with Arduino Uno — I2C temperature and humidity

The AHT20 is a small I2C temperature and humidity sensor that does the DHT22’s job more accurately, faster, and on a shared bus. A module costs about ₹120, often combined with a BMP280 pressure sensor on one board.

On the Uno it runs from 5V — the chip is rated up to 5.5 V — and wires to SDA/SCL, the same signals as A4/A5. It sits at I2C address 0x38, so it shares the bus with an LCD backpack or OLED without a clash.

The sketch reads temperature and humidity every 2 seconds with the Adafruit AHTX0 library.

Wiring

Board quirks

• Compared with a DHT22 it reads in about 80 ms, has no timing-critical protocol (so no interrupts are turned off), and shares the I2C bus with displays.
• The popular blue AHT20 + BMP280 combo board has both chips on one I2C bus: the AHT20 at 0x38 and the BMP280 at 0x77. This sketch reads the AHT20; add the BMP280 library for pressure.
• The Adafruit AHTX0 library pulls in Adafruit Unified Sensor and BusIO; this sketch uses about a quarter of the Uno’s 32 KB flash. Fine on its own, but count it if you add a graphics display.
• Mount it away from the Uno’s regulator and any USB charger — a degree of self-heating is common on a breadboard.

Code

// AHT20 temperature + humidity sensor on an Arduino Uno R3, I2C at 0x38.
// VCC → 5V, GND → GND, SCL → SCL (A5), SDA → SDA (A4).
#include <Wire.h>
#include <Adafruit_AHTX0.h>

Adafruit_AHTX0 aht;

void setup() {
  Serial.begin(9600);
  if (!aht.begin()) {
    Serial.println(F("AHT20 not found at 0x38 - check SDA/SCL"));
    for (;;) {}
  }
  Serial.println(F("AHT20 ready"));
}

void loop() {
  sensors_event_t humidity, temp;
  aht.getEvent(&humidity, &temp);
  Serial.print(F("Temp "));
  Serial.print(temp.temperature, 1);
  Serial.print(F(" C  Humidity "));
  Serial.print(humidity.relative_humidity, 1);
  Serial.println(F(" %"));
  delay(2000);  // AHT20 self-heats a little if read much faster
}

// AHT20 temperature + humidity sensor on an Arduino Uno R3, I2C at 0x38.
// VCC → 5V, GND → GND, SCL → SCL (A5), SDA → SDA (A4).
#include <Wire.h>
#include <Adafruit_AHTX0.h>

Adafruit_AHTX0 aht;

void setup() {
  Serial.begin(9600);
  if (!aht.begin()) {
    Serial.println(F("AHT20 not found at 0x38 - check SDA/SCL"));
    for (;;) {}
  }
  Serial.println(F("AHT20 ready"));
}

void loop() {
  sensors_event_t humidity, temp;
  aht.getEvent(&humidity, &temp);
  Serial.print(F("Temp "));
  Serial.print(temp.temperature, 1);
  Serial.print(F(" C  Humidity "));
  Serial.print(humidity.relative_humidity, 1);
  Serial.println(F(" %"));
  delay(2000);  // AHT20 self-heats a little if read much faster
}

Library: Adafruit AHTX0 (Adafruit) — compiled with Adafruit AHTX0 2.0.6.

Expected serial output

AHT20 ready
Temp 28.6 C  Humidity 63.4 %
Temp 28.6 C  Humidity 63.5 %

AHT20 ready
Temp 28.6 C  Humidity 63.4 %
Temp 28.6 C  Humidity 63.5 %

Common errors