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arduino-cli/libraries/BH1750/README.md
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arduino-cli/libraries/BH1750/README.md
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# BH1750
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[](https://travis-ci.org/claws/BH1750)<br>
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This package contains an Arduino library for digital light sensor breakout boards containing the
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BH1750FVI IC.
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The BH1750 board uses I2C for communication which requires two pins to
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communicate with the device. Configuring the I2C bus must be done in user code
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(not library code). This approach has been adopted so it can be done once and
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will better support the various options for different platforms.
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A common module containing the BH1750 component is the GY-30 shown below.
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## Overview
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The BH1750 has six different measurement modes which are divided in two groups;
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continuous and one-time measurements. In continuous mode the sensor
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continuously measures lightness value. In one-time mode, the sensor makes only
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one measurement and then goes into Power Down mode.
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Each mode has three different precisions:
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- Low Resolution Mode - (4 lx precision, 16ms measurement time)
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- High Resolution Mode - (1 lx precision, 120ms measurement time)
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- High Resolution Mode 2 - (0.5 lx precision, 120ms measurement time)
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By default, this library uses Continuous High Resolution Mode, but you can
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change this to a different mode by passing the mode argument to
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BH1750.begin().
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When the One-Time mode is used your sensor will go into Power Down mode when
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it completes the measurement and you've read it. When the sensor is powered up
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again it returns to the default mode which means it needs to be reconfigured
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back into One-Time mode. This library has been implemented to automatically
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reconfigure the sensor when you next attempt a measurement so you should not
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have to worry about such low level details.
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Usually you will get an integer value which represent the lux equivalent.
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- Low Resolution Mode - (generic range: 0.0 up to 54612.5 lux)
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- High Resolution Mode - (generic range: 0.0 up to 54612.5 lux)
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- High Resolution Mode 2 - (generic range: 0.0 up to 27306.25 lux)
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The sensor itself returns a 16 bit unsigned integer. Therefore the maximum value is limited in general.
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The standard conversion between the so called 'counts' to lux is 1/1.2, that means you get a smaller value.
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As we use float, if an error occurs you will get a negative value.
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- -1 no valid data was transmitted from the sensor
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- -2 device is not configured
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Otherwise the measured counts are converted to lux and returned. If no advanced parameters are changed the maximum lux value is 54612.5 lx.
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As the sensor counts impact of light in a specific time frame you could change this time frame.
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This is needed if you use an overlay windows or compensate environmental influence like darkness.
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This time frame is defined by a register which is called MTreg. Therefore you could choose a value between 32 and 254.
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The default value is 69; keep in mind that the measurement time is changed accordingly.
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The datasheet for the BH1750 chip can be obtained [here](http://www.elechouse.com/elechouse/images/product/Digital%20light%20Sensor/bh1750fvi-e.pdf)
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## Installation
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Click "Clone or download" -> "Download ZIP" button.
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- **(For Arduino >= 1.5.x)** Use the way above, or Library Manager. Open Arduino
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IDE, click `Sketch -> Include library -> Add .ZIP library ` and select the
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downloaded archive.
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- **(For Arduino < 1.5.x)** Extract the archive to
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``<Your User Directory>/My Documents/Arduino/libraries/`` folder and rename it
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to `BH1750`. Restart IDE.
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The following YouTube [video](https://youtu.be/ACTMQvPVMLs) (specifically from
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7:20 onwards) provides a good overview of installing this library and loading
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an example using the Arduino IDE.
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[](https://youtu.be/ACTMQvPVMLs?t=437)
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Additional info, about library installation process - https://www.arduino.cc/en/Guide/Libraries
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## Example
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An example using the BH1750 library in conjunction with the GY-30 board
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(which contains the BH1750 component) is presented below. The example
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code uses the BH1750 library in the default continuous high precision
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mode when making light measurements.
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### Wiring
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Connections:
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- VCC -> 3V3 or 5V
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- GND -> GND
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- SCL -> SCL (A5 on Arduino Nano, Uno, Leonardo, etc or 21 on Mega and Due, on esp8266 free selectable)
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- SDA -> SDA (A4 on Arduino Nano, Uno, Leonardo, etc or 20 on Mega and Due, on esp8266 free selectable)
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- ADD -> NC/GND or VCC (see below)
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The ADD pin is used to set the sensor I2C address. By default (if ADD voltage
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less than 0.7 * VCC) the sensor address will be 0x23. If it has voltage
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greater or equal to 0.7VCC voltage (e.g. you've connected it to VCC) the
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sensor address will be 0x5C.
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Wiring up the GY-30 sensor board to an Arduino is shown in the diagram below.
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*The image above was created using [Fritzing](http://fritzing.org/home/) and
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the GY-30 module was obtained from [here](http://omnigatherum.ca/wp/?p=6)*.
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### Code
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Upload the BH1750 test code to your Arduino.
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``` c++
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#include <Wire.h>
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#include <BH1750.h>
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BH1750 lightMeter;
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void setup(){
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Serial.begin(9600);
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// Initialize the I2C bus (BH1750 library doesn't do this automatically)
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// On esp8266 devices you can select SCL and SDA pins using Wire.begin(D4, D3);
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Wire.begin();
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lightMeter.begin();
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Serial.println(F("BH1750 Test"));
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}
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void loop() {
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float lux = lightMeter.readLightLevel();
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Serial.print("Light: ");
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Serial.print(lux);
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Serial.println(" lx");
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delay(1000);
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}
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```
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### Output
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Moving the sensor to face more light results in the lux measurements increasing.
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```
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BH1750 Test
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Light: 70.0 lx
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Light: 70.0 lx
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Light: 59.0 lx
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Light: 328.0 lx
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Light: 333.0 lx
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Light: 335.0 lx
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Light: 332.0 lx
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```
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There are more examples in the examples directory.
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