TheBH1750FVI device is a digital light intensity sensor which uses the I2C interface. This allows it to be connected to the Raspberry Pi with only four wires.
The module allows quick and cheap ambient light level measurement and the light level can be read from it as a digital number due to the built in 16-bit analogue-to-digital converter. The device itself is commonly used in mobile phones, LCD TVs and digital cameras.
The module I’ve got measures only 32 x 16mm. I soldered a five pin header onto the PCB and this allowed me to plug it onto a piece of breadboard.
The BH1750 Ambient Light Sensor IC datasheet provides all the technical details some of which are used in my example Python script.
Configure I2C Interface
In order to use this module you must enable the I2C interface on the Raspberry Pi as it is not enabled by default. This is a fairly easy process and is described in my Enabling The I2C Interface On The Raspberry Pi tutorial.
The following table shows how I connected the module pins on the PCB to the Pi’s GPIO header (P1). Please refer to my GPIO header guide for a diagram.
|Module PCB||Desc||GPIO Header Pins|
Here is a diagram of a breadboard setup. If you are connecting the module’s five pins directly to the Pi you only need five female-female wires.
This Fritzing diagram uses a custom part I created for my module. Other modules may have a different pin arrangement so make sure you are connecting the correct pins to the Pi if yours is slightly different.
With the device connected and the Pi powered up the “i2cdetect” command should show the device with address 0x23.
Example Python Code
Here is a simple Python script to read the light level from the module :
#!/usr/bin/python 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 + (256 * data)) / 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()
If you want download this script directly to your Pi you can use the following command :
or use this link in a browser.
In order to run it you can use :
sudo python bh1750.py
The output should look something like :
The while loop keeps taking readings every 200ms until you press CTRL-C.
Script Notes :
- The import statements import Python libraries used in the rest of the code including smbus which handles the I2C interface.
- All I2C devices must have an address. In this example I tied the ADDR pin to ground so the address used by the device is 0x23. If the ADDR pin is tied to 3.3V the address is 0x5C.
- The block of constants are listed in the datasheet and define the different modes the device can operate in. I define all of them but only use “ONE_TIME_HIGH_RES_MODE_1”. The other modes are only of any real interest if you need to take high speed readings.
- The “smbus.SMBus(1)” function setups the I2C interface.
- The “read_i2c_block_data” function is used to read 2 bytes of data from the device using the ONE_TIME_HIGH_RES_MODE_1.
- The convertToNumber function is then used to convert those 2 bytes of data into a number. The 1.2 value in the calculation is defined in the datasheet.
The module is available from eBay, Amazon and many other online electronics shops.