aht20 v0.1.0

AHT20 temperature and humidity sensor.

Application scenarios

• Low-cost room climate sensing.
• Enclosure temperature and humidity.
• A calibrated sensor with a digital I2C interface.

Contract

uint8_t aht20_init(aht20_t *device, aht20_port_t port, uint8_t i2c_address);
uint8_t aht20_read(aht20_t *device, int32_t *milli_celsius, int32_t *milli_percent);

• init waits for power-on, checks the calibration bit, and sends the

initialization command when needed.

• read triggers a measurement, waits 80 ms, and validates the CRC.
• Temperature is millidegrees Celsius; humidity is millipercent RH.
• Returns 1 on success, 0 on a bus error, a busy sensor, or a bad CRC.

Parameters

• I2C address 0x38.
• Measurement time is about 80 ms.
• Conversion: T = raw * 200 / 2^20 - 50, RH = raw * 100 / 2^20.

Memory and timing

• About 4 bytes; one 7-byte read.
• Do not trigger a new measurement before the previous one completes.

Integration

aht20_t sensor;
aht20_init(&sensor, board_i2c_port(), 0x38);
int32_t temperature, humidity;
if (aht20_read(&sensor, &temperature, &humidity)) {
    show(temperature / 1000, humidity / 1000);
}

Adapters

• The adapter writes a three-byte command and reads seven bytes.
• Reference: LibDriver aht20 (MIT) and the Aosong AHT20 datasheet.
• This implementation is original.

When not to use

• Condensing environments.
• A sensor that must be read faster than 10 Hz.

Verification

make test covers initialization, conversion, the busy status, and a bad CRC.

void *context;
uint8_t (*write)(void *context, uint8_t address, const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t *data, uint16_t length);
void (*delay_ms)(void *context, uint16_t milliseconds);

aht20_port_t port;
uint8_t i2c_address;