121 lines
4.3 KiB
Python
121 lines
4.3 KiB
Python
from smbus2 import SMBus
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import time
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from crc8_helper import AHT20_crc8_check
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def get_normalized_bit(value, bit_index):
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# Return only one bit from value indicated in bit_index
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return (value >> bit_index) & 1
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AHT20_I2CADDR = 0x38
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AHT20_CMD_SOFTRESET = [0xBA]
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AHT20_CMD_INITIALIZE = [0xBE, 0x08, 0x00]
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AHT20_CMD_MEASURE = [0xAC, 0x33, 0x00]
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AHT20_STATUSBIT_BUSY = 7 # The 7th bit is the Busy indication bit. 1 = Busy, 0 = not.
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AHT20_STATUSBIT_CALIBRATED = 3 # The 3rd bit is the CAL (calibration) Enable bit. 1 = Calibrated, 0 = not
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class AHT20:
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# I2C communication driver for AHT20, using only smbus2
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def __init__(self, BusNum=1):
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# Initialize AHT20
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self.BusNum = BusNum
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self.cmd_soft_reset()
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# Check for calibration, if not done then do and wait 10 ms
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if not self.get_status_calibrated == 1:
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self.cmd_initialize()
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while not self.get_status_calibrated() == 1:
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time.sleep(0.01)
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def cmd_soft_reset(self):
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# Send the command to soft reset
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with SMBus(self.BusNum) as i2c_bus:
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i2c_bus.write_i2c_block_data(AHT20_I2CADDR, 0x0, AHT20_CMD_SOFTRESET)
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time.sleep(0.04) # Wait 40 ms after poweron
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return True
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def cmd_initialize(self):
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# Send the command to initialize (calibrate)
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with SMBus(self.BusNum) as i2c_bus:
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i2c_bus.write_i2c_block_data(AHT20_I2CADDR, 0x0 , AHT20_CMD_INITIALIZE)
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return True
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def cmd_measure(self):
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# Send the command to measure
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with SMBus(self.BusNum) as i2c_bus:
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i2c_bus.write_i2c_block_data(AHT20_I2CADDR, 0, AHT20_CMD_MEASURE)
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time.sleep(0.08) # Wait 80 ms after measure
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return True
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def get_status(self):
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# Get the full status byte
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with SMBus(self.BusNum) as i2c_bus:
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return i2c_bus.read_i2c_block_data(AHT20_I2CADDR, 0x0, 1)[0]
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return True
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def get_status_calibrated(self):
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# Get the calibrated bit
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return get_normalized_bit(self.get_status(), AHT20_STATUSBIT_CALIBRATED)
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def get_status_busy(self):
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# Get the busy bit
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return get_normalized_bit(self.get_status(), AHT20_STATUSBIT_BUSY)
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def get_measure(self):
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# Get the full measure
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# Command a measure
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self.cmd_measure()
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# Check if busy bit = 0, otherwise wait 80 ms and retry
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while self.get_status_busy() == 1:
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time.sleep(0.08) # Wait 80 ns
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# TODO: do CRC check
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# Read data and return it
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with SMBus(self.BusNum) as i2c_bus:
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return i2c_bus.read_i2c_block_data(AHT20_I2CADDR, 0x0, 7)
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def get_measure_CRC8(self):
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"""
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This function will calculate crc8 code with G(x) = x8 + x5 + x4 + 1 -> 0x131(0x31), Initial value = 0xFF. No XOROUT.
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return: all_data (1 bytes status + 2.5 byes humidity + 2.5 bytes temperature + 1 bytes crc8 code), isCRC8_pass
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"""
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all_data = self.get_measure()
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isCRC8_pass = AHT20_crc8_check(all_data)
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return all_data, isCRC8_pass
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def get_temperature(self):
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# Get a measure, select proper bytes, return converted data
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measure = self.get_measure()
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measure = ((measure[3] & 0xF) << 16) | (measure[4] << 8) | measure[5]
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measure = measure / (pow(2,20))*200-50
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return measure
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def get_temperature_crc8(self):
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isCRC8Pass = False
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while (not isCRC8Pass):
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measure, isCRC8Pass = self.get_measure_CRC8()
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time.sleep(80 * 10**-3)
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measure = ((measure[3] & 0xF) << 16) | (measure[4] << 8) | measure[5]
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measure = measure / (pow(2,20))*200-50
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return measure
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def get_humidity(self):
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# Get a measure, select proper bytes, return converted data
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measure = self.get_measure()
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measure = (measure[1] << 12) | (measure[2] << 4) | (measure[3] >> 4)
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measure = measure * 100 / pow(2,20)
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return measure
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def get_humidity_crc8(self):
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isCRC8Pass = False
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while (not isCRC8Pass):
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measure, isCRC8Pass = self.get_measure_CRC8()
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time.sleep(80 * 10**-3)
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measure = (measure[1] << 12) | (measure[2] << 4) | (measure[3] >> 4)
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measure = measure * 100 / pow(2,20)
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return measure
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