I followed the recommendation of @paul- and changed to a solution based
on Python/smbus. The following replaces the part with C-programming and
the shell script in my previous how-to. All related to I2C is still
valid.
*Requirement:
*You just need to install the extension "smbus-python3.6.tcz". pCP will
add all dependencies, i.e. all other required extensions.
*Script:
*
Code:
--------------------
#!/usr/local/bin/python3
import smbus
import time
# Define some constants from the datasheet
ADDRESS = 0x23 # I2C-Adresse des BH1750 if ADDR is seto GND
#ADDRESS = 0x5C # I2C-Adresse des BH1750 if ADDR is seto 3.3V
POWER_DOWN = 0x00 # No active state
POWER_ON = 0x01 # Power on
RESET = 0x07 # Reset data register value
# Start measurement at 1 lx resolution. Time typically 120 ms
CONTINUOUS_HIGH_RES_MODE_1 = 0x10
# Start measurement at 1l x resolution. Time typically 120 ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_HIGH_RES_MODE_1 = 0x20
# Set DEBUG to 'True' if you want to print some debug info
DEBUG = False
# Creating an I2C instance
bh1750 = smbus.SMBus(1)
def convertToNumber(data):
# Simple function to convert 2 bytes of data
# into a decimal number. Optional parameter 'decimals'
# will round to specified number of decimal places.
result=(data[1] + (256 * data[0])) / 1.2
return (result)
def readLight(addr=ADDRESS):
# Read data from I2C interface
data = bh1750.read_i2c_block_data(addr,ONE_TIME_HIGH_RES_MODE_1)
return convertToNumber(data)
def calcTargetVal(lightLevel):
# Simple algorithm to calculate the new brightness value of the
# display.
MIN_THRESHOLD = 10 # minimum LUX value to consider
MAX_THRESHOLD = 1010 # maximum LUX value to consider
MIN_BRIGHTNESS = 10 # minimum brightness value of the display
MAX_BRIGHTNESS = 255 # maximum brightness value of the display
LUX_RANGE = MAX_THRESHOLD - MIN_THRESHOLD
BRIGHTNESS_RANGE = MAX_BRIGHTNESS - MIN_BRIGHTNESS
# STEPSIZE: actually the LUX value that represents one brightness step
STEPSIZE = LUX_RANGE / BRIGHTNESS_RANGE
if lightLevel < MIN_THRESHOLD:
target = MIN_BRIGHTNESS
elif lightLevel > MAX_THRESHOLD:
target = MAX_BRIGHTNESS
else:
target = MIN_BRIGHTNESS + ((lightLevel + MIN_THRESHOLD) // STEPSIZE)
return (int(target))
def main():
while True:
# Measuring the current LUX value
lightLevel=readLight()
if DEBUG:
print("Light Level : " + format(lightLevel,'.2f') + " lx")
# Calculating the target brightness of the display
dsply_brightness = calcTargetVal(lightLevel)
# Setting the brightness value of the display
dsply_file = '/sys/class/backlight/rpi_backlight/brightness'
f = open(dsply_file, 'wt')
f.write(str(dsply_brightness))
f.close()
if DEBUG:
print("Display: " + str(dsply_brightness))
# Wait 5 seconds before the next calculation
time.sleep(5)
# main() is only invoked if display-control.py runs as a script
if __name__=="__main__":
main()
--------------------
I stored this script as "display-control.py" in the folder
/home/tc/lux/.
To ensure that the Python script is executed with startup of pCP, it
must be started by the boot script /opt/bootlocal.sh. Together with the
I2C stuff, I added the following lines to /opt/bootlocal.sh:
Code:
--------------------
### BH1750 start ------
# Enabling kernel module i2c-dev
/sbin/modprobe i2c-dev
# starting shell script to control display brightness
/home/tc/lux/display-control.py
### BH1750 stop ------
--------------------
This solution runs since yesterday on the pCP in my bedroom and I am
happy with it.
------------------------------------------------------------------------
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View this thread: http://forums.slimdevices.com/showthread.php?t=112460
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