Initial upload for the HTU21D Humidity Sensor

Author: randymxj

Adafruit_HTU21D/Adafruit_HTU21D.py

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+#!/usr/bin/python
+
+import time
+from Adafruit_I2C import Adafruit_I2C
+
+# ===========================================================================
+# HTU21D Class
+# ===========================================================================
+
+class HTU21D:
+	i2c = None
+  
+	# HTU21D Address
+	address = 0x40
+	
+	# Commands
+	TRIGGER_TEMP_MEASURE_HOLD = 0xE3
+	TRIGGER_HUMD_MEASURE_HOLD = 0xE5
+	READ_USER_REG = 0xE7
+
+	# Constructor
+	def __init__(self):
+		self.i2c = Adafruit_I2C(self.address)
+		
+	def readUserRegister(self):
+		# Read a byte
+		value = self.i2c.readU8(self.READ_USER_REG)
+		
+		return value
+	
+	def readTemperatureData(self):
+		# value[0], value[1]: Raw temperature data
+		# value[2]: CRC
+		value = self.i2c.readList(self.TRIGGER_TEMP_MEASURE_HOLD, 3)
+		
+		if not self.crc8check(value):
+			return -255
+			
+		rawTempData = ( value[0] << 8 ) + value[1]
+		
+		# Zero out the status bits but keep them in place
+		rawTempData = rawTempData & 0xFFFC;
+		
+		# Calculate the actual temperature
+		actualTemp = -46.85 + (175.72 * rawTempData / 65536)
+		
+		return actualTemp
+
+	def readHumidityData(self):
+		# value[0], value[1]: Raw relative humidity data
+		# value[2]: CRC
+		value = self.i2c.readList(self.TRIGGER_HUMD_MEASURE_HOLD, 3)
+		
+		if not self.crc8check(value):
+			return -255
+
+		rawRHData = ( value[0] << 8 ) + value[1]
+		
+		# Zero out the status bits but keep them in place
+		rawRHData = rawRHData & 0xFFFC;
+		
+		# Calculate the actual RH
+		actualRH = -6 + (125.0 * rawRHData / 65536)
+		
+		return actualRH
+	
+	def crc8check(self, value):
+		remainder = ( ( value[0] << 8 ) + value[1] ) << 8
+		remainder |= value[2]
+		
+		# POLYNOMIAL = 0x0131 = x^8 + x^5 + x^4 + 1
+		# divsor = 0x988000 is the 0x0131 polynomial shifted to farthest left of three bytes
+		divsor = 0x988000
+		
+		for i in range(0, 16):
+			if( remainder & 1 << (23 - i) ):
+				remainder ^= divsor
+
+			divsor = divsor >> 1
+		
+		if remainder == 0:
+			return True
+		else:
+			return False
+	

Adafruit_HTU21D/Adafruit_HTU21D_example.py

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+#!/usr/bin/python
+
+import time
+from Adafruit_HTU21D import HTU21D
+
+# ===========================================================================
+# Example Code
+# ===========================================================================
+
+# Initialise the HTU21D
+htu = HTU21D()
+
+for _ in range(100):
+	temp = htu.readTemperatureData()
+	rh = htu.readHumidityData()
+	
+	if temp > 0 and rh > 0:
+		print "Temperature: %.2f C, Humidity: %.2f %%" % (temp, rh)
+	elif temp == -255:
+		print "Temperature data CRC failed"
+	elif rh == -255:
+		print "RH data CRC failed"
+	else:
+		print "Invalid:" + str(temp) + ", " + str(rh)
+	
+	time.sleep(1)
+	

Adafruit_HTU21D/Adafruit_I2C.py

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+../Adafruit_I2C/Adafruit_I2C.py