Adolfo Reyna
87 lines
2.7 KiB
Python
87 lines
2.7 KiB
Python
import time
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from machine import I2C, Pin
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class SHTC3:
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"""Utility class for Sensirion SHTC3 Temperature and Humidity Sensor."""
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ADDR = 0x70
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# Commands
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WAKE = b'\x35\x17'
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SLEEP = b'\xB0\x98'
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MEASURE = b'\x78\x66' # High precision, T first, clock stretching disabled
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def __init__(self, i2c=None):
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if i2c is None:
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# Default to ESP32-S3-RLCD-4.2 onboard I2C pins
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from machine import SoftI2C
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self.i2c = SoftI2C(sda=Pin(13), scl=Pin(14))
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else:
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self.i2c = i2c
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def _crc8(self, data):
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"""Sensirion CRC-8 checksum calculation (polynom 0x31, init 0xFF)."""
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crc = 0xFF
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for byte in data:
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crc ^= byte
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for _ in range(8):
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if crc & 0x80:
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crc = (crc << 1) ^ 0x31
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else:
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crc <<= 1
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crc &= 0xFF
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return crc
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def read_sensor(self):
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"""Wakes up the sensor, reads temp and humidity, validates CRC, and sleeps.
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Returns:
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tuple: (temperature_c, relative_humidity_pct) or (None, None) on error.
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"""
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try:
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# 1. Wakeup
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self.i2c.writeto(self.ADDR, self.WAKE)
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time.sleep_ms(1)
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# 2. Trigger Measurement
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self.i2c.writeto(self.ADDR, self.MEASURE)
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time.sleep_ms(15) # High precision measurement takes up to 12.1ms
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# 3. Read 6 bytes of data
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# bytes 0, 1: Temp, byte 2: Temp CRC
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# bytes 3, 4: Hum, byte 5: Hum CRC
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data = self.i2c.readfrom(self.ADDR, 6)
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# 4. Enter low-power sleep mode
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self.i2c.writeto(self.ADDR, self.SLEEP)
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# Verify CRC
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t_data = data[0:2]
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t_crc = data[2]
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h_data = data[3:5]
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h_crc = data[5]
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if self._crc8(t_data) != t_crc:
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print("SHTC3 Temp CRC error")
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return None, None
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if self._crc8(h_data) != h_crc:
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print("SHTC3 Hum CRC error")
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return None, None
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raw_t = (data[0] << 8) | data[1]
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raw_h = (data[3] << 8) | data[4]
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# Formula from datasheet
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temp = -45.0 + 175.0 * (raw_t / 65536.0)
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hum = 100.0 * (raw_h / 65536.0)
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return round(temp, 2), round(hum, 2)
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except Exception as e:
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print(f"Error reading SHTC3 sensor: {e}")
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# Try to send sleep command anyway to save power
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try:
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self.i2c.writeto(self.ADDR, self.SLEEP)
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except:
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pass
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return None, None
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