WeatherOS/sht41.py at main · ohiomichael/WeatherOS · GitHub

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# SHT41 Driver Library
import time
from machine import I2C

class SHT41:
    # Device address
    ADDRESS = 0x44

    # Commands
    CMD_RESET = b'\x94'
    CMD_SERIAL = b'\x89'
    CMD_MEASURE_HIGH = b'\xFD'
    CMD_MEASURE_MED = b'\xF6'
    CMD_MEASURE_LOW = b'\xE0'

    def __init__(self, i2c: I2C):
        self.i2c = i2c
        self.reset()  # Reset on initialization
        time.sleep(0.01)  # Wait after reset

    def reset(self):
        """Soft reset the sensor"""
        try:
            self.i2c.writeto(self.ADDRESS, self.CMD_RESET)
            time.sleep(0.01)  # Wait for reset to complete
            return True
        except Exception as e:
            print(f"Reset error: {e}")
            return False

    def _crc8(self, data):
        """Calculate CRC8 checksum"""
        crc = 0xFF
        for byte in data:
            crc ^= byte
            for _ in range(8):
                if crc & 0x80:
                    crc = (crc << 1) ^ 0x31
                else:
                    crc <<= 1
            crc &= 0xFF
        return crc

    def read_serial(self):
        """Read the sensor serial number"""
        try:
            self.i2c.writeto(self.ADDRESS, self.CMD_SERIAL)
            time.sleep(0.01)
            data = self.i2c.readfrom(self.ADDRESS, 6)
            return data
        except Exception as e:
            print(f"Serial read error: {e}")
            return None

    def read(self, precision="high"):
        """
        Read temperature and humidity from the sensor
        precision: "high", "medium", or "low" (affects measurement time)
        """
        # Select command based on precision
        if precision == "medium":
            cmd = self.CMD_MEASURE_MED
        elif precision == "low":
            cmd = self.CMD_MEASURE_LOW
        else:  # Default to high precision
            cmd = self.CMD_MEASURE_HIGH

        # Delay times for different precision levels
        delays = {"high": 0.01, "medium": 0.005, "low": 0.002}

        try:
            # Send measurement command
            self.i2c.writeto(self.ADDRESS, cmd)

            # Wait for measurement to complete
            time.sleep(delays[precision])

            # Read 6 bytes: temp (2) + CRC (1) + humidity (2) + CRC (1)
            raw = self.i2c.readfrom(self.ADDRESS, 6)

            # Parse data
            temp_raw = raw[0:2]
            temp_crc = raw[2]
            hum_raw = raw[3:5]
            hum_crc = raw[5]

            # Verify checksums
            if self._crc8(temp_raw) != temp_crc or self._crc8(hum_raw) != hum_crc:
                raise ValueError("CRC check failed")

            # Convert raw values to temperature and humidity
            temp_ticks = (temp_raw[0] << 8) | temp_raw[1]
            hum_ticks = (hum_raw[0] << 8) | hum_raw[1]

            # Apply conversion formulas from datasheet
            temperature = -45 + (175 * temp_ticks / 65535.0)
            humidity = 100 * hum_ticks / 65535.0

            return temperature, humidity

        except Exception as e:
            raise Exception(f"Measurement error: {e}")