Light Sensor

Published by Martin on July 28, 2020

A Light sensor seemed like a simple idea. Bought a new one from Core Electronics delivered very quickly again.. This is how it went.

BH1750 is a digital Ambient Light Sensor IC with an I2C bus interface. The module does all of the hard work, providing a simple digital value via I2C that represents luminance (Lux).

Description:

Model: GY-302
Chip: BH1750FVI
Power supply :3-5V
Data output range resembles luminance from 0-65535 lux
I2C Interface
No external parts required
Dimensions: 13.9mm X 18.5mm
BH1750FVI Datasheet

#!/usr/bin/python3
#---------------------------------------------------------------------
#    ___  ___  _ ____
#   / _ \/ _ \(_) __/__  __ __
#  / , _/ ___/ /\ \/ _ \/ // /
# /_/|_/_/  /_/___/ .__/\_, /
#                /_/   /___/
#
#           bh1750.py
# Read data from a BH1750 digital light sensor.
#
# Author : Matt Hawkins
# Date   : 26/06/2018
#
# For more information please visit :
# https://www.raspberrypi-spy.co.uk/?s=bh1750
#
#---------------------------------------------------------------------
import smbus2 as 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. Optional parameter 'decimals'
  # will round to specified number of decimal places.
  result=(data[1] + (256 * data[0])) / 1.2
  return (result)

def readLight(addr=DEVICE):
  # Read data from I2C interface
  data = bus.read_i2c_block_data(addr,ONE_TIME_HIGH_RES_MODE_1,2)
  return convertToNumber(data)


lightLevel=readLight()
print("Light Level : " + format(lightLevel,'.2f') + " lx")

Core Electronics was the best place to get one of these : Core Electronics