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AHT20 / BMP280 sensor script for Arduino

  • This is an AHT20 / BMP280 temperature/pressure/humidity sensor script for Arduino.
  • AHT20 + BMP280 chips are sold for less than a dollar on Ali.
  • This script only uses the Wire.h library, nothing else.
  • Works with ESP8266, ESP32 and similar

AHT20_BMP280 logo

Arduino script features

  • Read temperature / humidity from AHT20
  • Read temperature / pressure from BMP280
  • No long loop times when reading the AHT20
  • Non blocking
  • Simple and clearly written
  • So that even beginners (like me) can understand how it works

How does it work

AHT20

The ATH20 can be reached via the address 0x38 So every query must begin with:

Wire.beginTransmission(0x38);

To initiate the AHT20, 0xBE must be sent. void AHT20_begin()

Wire.write(0xBE);

To start the measurement 0xAC, 0x33, 0x00 must be sent. void startMeasurementAHT20()

Wire.write(0xAC);  
Wire.write(0x33);  
Wire.write(0x00);

Now you have to wait until the data is available. ARAIR specifies a waiting time of 80ms. At the same time, the “Busy indication” bit must be monitored; if this is “0”, the measurement is finished. void checkbusyAHT20()

if (sensor_started && sensor_busy && ((millis() - measurementDelayAHT20 >= 80))) {
    Wire.requestFrom(0x38, 1);
    .
    .
    .

The 8 bytes of data can now be called up. void getDataAHT20()

Wire.requestFrom(0x38, 7);

The bytes read in can now be processed as shown below

+------------------+
| Byte 0: 00011000 |
| Byte 1: 10010011 |
| Byte 2: 10101100 |
| Byte 3: 10010101 |
| Byte 4: 00101010 |
| Byte 5: 11000101 |
| Byte 6: 10110011 |
+------------------+

    
+----------------------------+----------------------------+
| Humidity (raw)             | Temperature (raw)          |
+----------------------------+----------------------------+
| 10010011   10101100   1001 | 0101   00101010   11000101 |
|   (B1)       (B2)     (B3) | (B3)     (B4)       (B5)   |
+----------------------------+----------------------------+

+----------------------------------+
|          Berechnung Humi         |
|  10010011101011001001 = 604873   |
|  604873 / 1048576 * 100 = 57.69  |
+----------------------------------+

+-------------------------------------------+
|          Berechnung Temp                  |
|       01010010101011000101 = 338629       |
|  338629 / 1048576 * 200.0 - 50.0 = 14.59  |
+-------------------------------------------+


Humidity: 57.69%. Temperature: 14.59

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