AHT20 on OLED: Temperature & Humidity
Overview & Wiring
What it is: The AHT20 is a small, cheap, accurate I2C temperature and humidity sensor (±0.3 °C, ±2 % RH). It's a popular modern replacement for the DHT22 and is often sold on the same board as a BMP280.
How it works: Pure I2C, fixed address 0x38, so it shares the OLED's SDA/SCL. The Adafruit AHTX0 library returns temperature and humidity as sensor events.
Wiring (shared I2C bus with the OLED):
AHT20 SDA -> GPIO4
AHT20 SCL -> GPIO5
AHT20 VCC -> 3V3
AHT20 GND -> GND
OLED VCC=3V3, GND=GND, SDA=GPIO4, SCL=GPIO5
Libraries: "Adafruit AHTX0" (installs "Adafruit BusIO" and "Adafruit Unified Sensor"), plus "Adafruit SSD1306" and "Adafruit GFX Library".
On screen / Serial: temperature (°C) and humidity (%), one decimal.
Gotchas: The AHT20's address (0x38) is fixed and can't be changed, so you can't put two on one bus. It shares a bus fine with the OLED (0x3C) and a BMP280 (0x76).
Circuit Diagram
Parts You Need
Source Code (Arduino / ESP32)
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_AHTX0.h>
Adafruit_SSD1306 display(128, 64, &Wire, -1);
Adafruit_AHTX0 aht;
void setup() {
Serial.begin(115200);
Wire.begin(4, 5);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
if (!aht.begin()) {
Serial.println("AHT20 not found");
display.setTextColor(SSD1306_WHITE);
display.setCursor(0, 28); display.println("AHT20 not found");
display.display();
while (1) delay(10);
}
}
void loop() {
sensors_event_t humidity, temp;
aht.getEvent(&humidity, &temp); // fills both structs
display.clearDisplay();
display.setTextColor(SSD1306_WHITE);
display.setTextSize(1);
display.setCursor(0, 0);
display.println("AHT20");
display.setTextSize(2);
display.setCursor(0, 18); display.printf("%.1f C", temp.temperature);
display.setCursor(0, 42); display.printf("%.1f %%", humidity.relative_humidity);
display.display();
Serial.printf("Temp %.1f C Hum %.1f %%\n", temp.temperature, humidity.relative_humidity);
delay(1000);
}