Need help creating a python script to access an HTU21D

Question

I have a Raspberry PI 2 and I am having a hard time getting any scripts that work to read the HTU21D-F.

This the errors I am getting.

Traceback (most recent call last): File "Adafruit_HTU21D_example.py", line 14, in temp = htu.readTemperatureData() File "/home/pi/Adafruit_HTU21D/Adafruit_HTU21D.py", line 36, in readTemperatureData value = self.i2c.readList(self.TRIGGER_TEMP_MEASURE_HOLD, 3) File "/home/pi/Adafruit_HTU21D/Adafruit_I2C.py", line 94, in readList results = self.bus.read_i2c_block_data(self.address, reg, length) AttributeError: 'Adafruit_I2C' object has no attribute 'bus'

This the script I run.

#!/usr/bin/python

import time
from Adafruit_HTU21D import HTU21D

# Initialise the HTU21D
htu = HTU21D()

for _ in range(100):
temp = htu.readTemperatureData()
rh = htu.readHumidityData()

if temp > -40 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)

Supporting file 1.

#!/usr/bin/python

import time
from Adafruit_I2C import Adafruit_I2C

# =========================================================================
# HTU21D Class
# 
# Code only test with a Sparkfun HTU21D Sensor module on a Beaglebone Black.
# It has been reported that an I2C address issue was seen on a Pi.
# =========================================================================

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 the user register byte"
    return self.i2c.readU8(self.READ_USER_REG)

def readTemperatureData(self):
    "Read 3 temperature bytes from the sensor"
    # value[0], value[1]: Raw temperature data
    # value[2]: CRC
    value = self.i2c.readList(self.TRIGGER_TEMP_MEASURE_HOLD, 3)

    # CRC Check
    if not self.crc8check(value):
        return -255

    rawTempData = ( value[0] << 8 ) + value[1]

    # Clear the status bits
    rawTempData = rawTempData & 0xFFFC;

    # Calculate the actual temperature
    actualTemp = -46.85 + (175.72 * rawTempData / 65536)

    return actualTemp

def readHumidityData(self):
    "Read 3 humidity bytes from the sensor"
    # value[0], value[1]: Raw relative humidity data
    # value[2]: CRC
    value = self.i2c.readList(self.TRIGGER_HUMD_MEASURE_HOLD, 3)

    # CRC Check
    if not self.crc8check(value):
        return -255

    rawRHData = ( value[0] << 8 ) + value[1]

    # Clear the status bits
    rawRHData = rawRHData & 0xFFFC;

    # Calculate the actual RH
    actualRH = -6 + (125.0 * rawRHData / 65536)

    return actualRH

 def crc8check(self, value):
    "Calulate the CRC8 for the data received"
    # Ported from Sparkfun Arduino HTU21D Library:   https://github.com/sparkfun/HTU21D_Breakout
    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

Supporting file 2.

#!/usr/bin/python

import smbus

# =========================================================================
# Adafruit_I2C Class
# =========================================================================

class Adafruit_I2C(object):

    @staticmethod
      def getPiRevision():
      "Gets the version number of the Raspberry Pi board"
# Courtesy quick2wire-python-api
# https://github.com/quick2wire/quick2wire-python-api
# Updated revision info from: http://elinux.org/RPi_HardwareHistory#Board_Revision_History
try:
  with open('/proc/cpuinfo','r') as f:
    for line in f:
      if line.startswith('Revision'):
        return 1 if line.rstrip()[-1] in ['2','3'] else 2
except:
  return 0

@staticmethod
def getPiI2CBusNumber():
# Gets the I2C bus number /dev/i2c#
return 1 if Adafruit_I2C.getPiRevision() > 1 else 0

def __init__(self, address, busnum=-1, debug=False):
self.address = address
# By default, the correct I2C bus is auto-detected using /proc/cpuinfo
# Alternatively, you can hard-code the bus version below:
# self.bus = smbus.SMBus(0); # Force I2C0 (early 256MB Pi's)
self.bus = smbus.SMBus(1); # Force I2C1 (512MB Pi's) # UNCOMMENT THIS LINE
#self.bus = smbus.SMBus(busnum if busnum >= 0 else       Adafruit_I2C.getPiI2CBusNumber())
self.debug = debug

def reverseByteOrder(self, data):
 "Reverses the byte order of an int (16-bit) or long (32-bit) value"
# Courtesy Vishal Sapre
byteCount = len(hex(data)[2:].replace('L','')[::2])
val       = 0
for i in range(byteCount):
  val    = (val << 8) | (data & 0xff)
  data >>= 8
return val

def errMsg(self):
 print "Error accessing 0x%02X: Check your I2C address" % self.address
 return -1

 def write8(self, reg, value):
  "Writes an 8-bit value to the specified register/address"
   try:
    self.bus.write_byte_data(self.address, reg, value)
    if self.debug:
    print "I2C: Wrote 0x%02X to register 0x%02X" % (value, reg)
 except IOError, err:
  return self.errMsg()

 def write16(self, reg, value):
  "Writes a 16-bit value to the specified register/address pair"
    try:
      self.bus.write_word_data(self.address, reg, value)
      if self.debug:
       print ("I2C: Wrote 0x%02X to register pair 0x%02X,0x%02X" %
       (value, reg, reg+1))
  except IOError, err:
  return self.errMsg()

 def writeRaw8(self, value):
   "Writes an 8-bit value on the bus"
     try:
      self.bus.write_byte(self.address, value)
  if self.debug:
    print "I2C: Wrote 0x%02X" % value
   except IOError, err:
     return self.errMsg()

  def writeList(self, reg, list):
"Writes an array of bytes using I2C format"
try:
  if self.debug:
    print "I2C: Writing list to register 0x%02X:" % reg
    print list
  self.bus.write_i2c_block_data(self.address, reg, list)
except IOError, err:
  return self.errMsg()

 def readList(self, reg, length):
"Read a list of bytes from the I2C device"
try:
  results = self.bus.read_i2c_block_data(self.address, reg, length)
  if self.debug:
    print ("I2C: Device 0x%02X returned the following from reg 0x%02X" %
     (self.address, reg))
    print results
  return results
except IOError, err:
  return self.errMsg()

 def readU8(self, reg):
"Read an unsigned byte from the I2C device"
try:
  result = self.bus.read_byte_data(self.address, reg)
  if self.debug:
    print ("I2C: Device 0x%02X returned 0x%02X from reg 0x%02X" %
     (self.address, result & 0xFF, reg))
  return result
except IOError, err:
  return self.errMsg()

def readS8(self, reg):
"Reads a signed byte from the I2C device"
try:
  result = self.bus.read_byte_data(self.address, reg)
  if result > 127: result -= 256
  if self.debug:
    print ("I2C: Device 0x%02X returned 0x%02X from reg 0x%02X" %
     (self.address, result & 0xFF, reg))
  return result
except IOError, err:
  return self.errMsg()

def readU16(self, reg, little_endian=True):
"Reads an unsigned 16-bit value from the I2C device"
try:
  result = self.bus.read_word_data(self.address,reg)
  # Swap bytes if using big endian because read_word_data assumes little 
  # endian on ARM (little endian) systems.
  if not little_endian:
    result = ((result << 8) & 0xFF00) + (result >> 8)
  if (self.debug):
    print "I2C: Device 0x%02X returned 0x%04X from reg 0x%02X" % (self.address, result & 0xFFFF, reg)
  return result
except IOError, err:
  return self.errMsg()

def readS16(self, reg, little_endian=True):
"Reads a signed 16-bit value from the I2C device"
try:
  result = self.readU16(reg,little_endian)
  if result > 32767: result -= 65536
  return result
except IOError, err:
  return self.errMsg()

if __name__ == '__main__':
  try:
   bus = Adafruit_I2C(address=0)
   print "Default I2C bus is accessible"
  except:
   print "Error accessing default I2C bus"

Answer 1

Ok this did not resolve my issue with this code but it did help in getting the issue fixed. I had to run sudo asps-config and enable the IC2 on boot. Then after looking at the code for 20 hours I noticed that I need to remove the # from the line with self.bus = smbus.SMBus(1); # Force I2C1 (512MB Pi's).