bh1750.py

#!/usr/bin/python
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#  / , _/ ___/ /\ \/ _ \/ // / 
# /_/|_/_/  /_/___/ .__/\_, /  
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#
#           bh1750.py
#  Read data from a digital light sensor.
#
# Author : Matt Hawkins
# Date   : 15/04/2015
#
# http://www.raspberrypi-spy.co.uk/
#
#--------------------------------------
import smbus
import time
 
# Define some constants from the datasheet
 
DEVICE     = 0x23 # Default device I2C address
 
POWER_DOWN = 0x00 # No active state
POWER_ON   = 0x01 # Power on
RESET      = 0x07 # Reset data register value
 
# Start measurement at 4lx resolution. Time typically 16ms.
CONTINUOUS_LOW_RES_MODE = 0x13
# Start measurement at 1lx resolution. Time typically 120ms
CONTINUOUS_HIGH_RES_MODE_1 = 0x10
# Start measurement at 0.5lx resolution. Time typically 120ms
CONTINUOUS_HIGH_RES_MODE_2 = 0x11
# Start measurement at 1lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_HIGH_RES_MODE_1 = 0x20
# Start measurement at 0.5lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_HIGH_RES_MODE_2 = 0x21
# Start measurement at 1lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_LOW_RES_MODE = 0x23
 
#bus = smbus.SMBus(0) # Rev 1 Pi uses 0
bus = smbus.SMBus(1)  # Rev 2 Pi uses 1
 
def convertToNumber(data):
  # Simple function to convert 2 bytes of data
  # into a decimal number
  return ((data[1] + (256 * data[0])) / 1.2)
 
def readLight(addr=DEVICE):
  data = bus.read_i2c_block_data(addr,ONE_TIME_HIGH_RES_MODE_1)
  return convertToNumber(data)
 
def main():
 
  while True:
    print ("Light Level : " + str(readLight()) + " lx")
    time.sleep(0.5)
   
if __name__=="__main__":
   main()