embedded-dht-rs 0.3.2

A platform agnostic driver to interface with the DHT11 / DHT20 (AHT20) / DHT22 (AM2302) temperature and humidity sensor
Documentation 
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use embedded_hal::{delay::DelayNs, i2c::I2c};

use crate::{SensorError, SensorReading};

pub struct Dht20<I: I2c, D: DelayNs> {
    pub i2c: I,
    pub delay: D,
}

impl<I: I2c, D: DelayNs> Dht20<I, D> {
    const SENSOR_ADDRESS: u8 = 0x38;

    pub fn new(i2c: I, delay: D) -> Self {
        Self { i2c, delay }
    }

    pub fn read(&mut self) -> Result<SensorReading<f32>, SensorError> {
        // Check status
        let mut status_response: [u8; 1] = [0; 1];
        let _ = self
            .i2c
            .write_read(Self::SENSOR_ADDRESS, &[0x71], &mut status_response);

        // Callibration if needed
        if status_response[0] & 0x18 != 0x18 {
            let _ = self.i2c.write(Self::SENSOR_ADDRESS, &[0x1B, 0, 0]);
            let _ = self.i2c.write(Self::SENSOR_ADDRESS, &[0x1C, 0, 0]);
            let _ = self.i2c.write(Self::SENSOR_ADDRESS, &[0x1E, 0, 0]);
        }

        // Trigger the measurement
        self.delay.delay_ms(10);
        let _ = self.i2c.write(Self::SENSOR_ADDRESS, &[0xAC, 0x33, 0x00]);

        // Read the measurement status
        self.delay.delay_ms(80);
        loop {
            let mut measurement_status_response: [u8; 1] = [0; 1];
            let _ = self
                .i2c
                .read(Self::SENSOR_ADDRESS, &mut measurement_status_response);
            let status_word = measurement_status_response[0];
            if status_word & 0b1000_0000 == 0 {
                break;
            }
            self.delay.delay_ms(1);
        }

        // Read the measurement (1 status + 5 data + 1 crc)
        let mut measurement_response: [u8; 7] = [0; 7];
        let _ = self
            .i2c
            .read(Self::SENSOR_ADDRESS, &mut measurement_response);

        // Humidity 20 bits (8 + 8 + 4)
        let mut raw_humidity = measurement_response[1] as u32;
        raw_humidity = (raw_humidity << 8) + measurement_response[2] as u32;
        raw_humidity = (raw_humidity << 4) + (measurement_response[3] >> 4) as u32;
        let humidity_percentage = (raw_humidity as f32 / ((1 << 20) as f32)) * 100.0;

        // Temperature 20 bits
        let mut raw_temperature = (measurement_response[3] & 0b1111) as u32;
        raw_temperature = (raw_temperature << 8) + measurement_response[4] as u32;
        raw_temperature = (raw_temperature << 8) + measurement_response[5] as u32;
        let temperatue_percentage = (raw_temperature as f32 / ((1 << 20) as f32)) * 200.0 - 50.0;

        // Compare the calculated CRC with the received CRC
        let data = &measurement_response[..6];
        let received_crc = measurement_response[6];
        let calculcated_crc = Self::calculate_crc(data);
        if received_crc != calculcated_crc {
            return Err(SensorError::ChecksumMismatch);
        }

        Ok(SensorReading {
            humidity: humidity_percentage,
            temperature: temperatue_percentage,
        })
    }

    fn calculate_crc(data: &[u8]) -> u8 {
        let polynomial = 0x31u8; // x^8 + x^5 + x^4 + 1
        let mut crc = 0xFFu8;

        for &byte in data {
            crc ^= byte;
            // CRC8 - process every bit
            for _ in 0..8 {
                if crc & 0x80 != 0 {
                    crc = (crc << 1) ^ polynomial;
                } else {
                    crc <<= 1;
                }
            }
        }

        crc
    }
}