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bh1750.py
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bh1750.py
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#!/usr/bin/python
import smbus
import time
import math
# Define some constants from the datasheet
DEVICE = 0x23 # Default device's 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 (also apply to Rpi 3B 2015)
# Define the maximum brightness level that would
# cause the curtain to close all the way
maxBrightness = 65000 # not sure, might need to check and re-adjust
def convertToNumber(data):
# Simple function to convert 2 bytes of data into a float decimal number
return ((data[1] + (256 * data[0])) / 1.2)
def readLight(addr=DEVICE): # input is by default the device's I2C address
# Just need to know that this function returns a float decimal number
data = bus.read_i2c_block_data(addr,ONE_TIME_HIGH_RES_MODE_1)
return convertToNumber(data)
def main():
light_level = 0
while True: # Python's version of a loop that runs forever
if math.isclose(readLight(), light_level, rel_tol=1e-2):
print("Light Level : " + str('{0:.3f}'.format(readLight())) + " lux")
light_level = readLight()
# Continuously updated variable on what percentage the curtain should close/open
curtainPercent = readLight()/maxBrightness
time.sleep(0.5) # Should change this time interval between measurements to be longer
if __name__=="__main__":
main()