BH1750 – Specifications and Applications

Light is necessary for the sense of sight. Light is a form of electromagnetic radiation. It carries energy in the form of small energy packets called Photons. The energy in the photon is transferred to the objects when they come in its contact. This characteristic of light is used in designing sensors that can detect light. These sensors known as light sensors, absorb the energy from light and change into electricity with the help of the photoelectric effect. The electricity produced will be proportional to the intensity of light which falls on the sensor and sensor material. With this principle, different wavelengths of light such as UV, IR, Ambient light, etc… can be measured. BH1750 is the sensor designed to measure ambient light.

What is BH1750?

BH1750 is a Digital Ambient light sensor. It is easy to interface with a microcontroller, as it uses the I2C communication protocol. It consumes a very low amount of current. This sensor uses a photodiode to sense the light. This photodiode contains a PN junction. When light falls on it, electron-hole pairs are created in the depletion region. Due to the internal photoelectric effect, electricity is produced in the photodiode. This produced electricity is proportional to the intensity of light. This electricity is changed into a voltage by the Opamp.

Block Diagram of BH1750

Ambient light sensors contain a photodiode that can sense light and convert it into electricity. Light is measured depending upon its intensity. From the block diagram, PD is the photodiode which is used to sense the light. Its response is approximate to the human eye response.

In BH1750 sensor an Opamp – AMP is integrated which converts the current from the photodiode into voltage. BH1750 uses an ADC to convert the analog values provided by AMP into digital values. The logic+I2C block shown in the block diagram is the unit where illuminance values are converted to LUX and the I2C communication process takes place. OSC is the internal clock oscillator of 320kHz, used as a clock for internal logic.

Circuit Diagram

BH1750 works with a supply voltage of 2.4V to 3.6V. BH1750FVI is the main module of the sensor which requires 3.3V for working. So, a voltage regulator is used in the circuit. SDA and SCL are the pins used for I2C communication. 4.7kΩ of pullup resistors are used with these pins.

There are three types of measurement modes for BH1750. H-resolution mode2 takes 120ms for measurement and has an 0.5 lx of resolution. H-resolution mode also takes 120ms for measurement but its resolution is 1 lx. L- resolution takes 16ms for measurement and its resolution is 4 lx. H- resolution mode is more useful in darkness and it can also easily reject noise.

Pin Diagram

BH1750 is available as a 5-pin IC. Pin description of the IC is given below-

• Pin1- Vcc – is the power supply pin. The supply voltage is in the range of 2.4V to 3.6V.
• Pin-2 – GND- is the ground pin. This pin is connected to the ground of the circuit.
• Pin-3 – SCL- is the Serial Clock Line. This pin is used to provide a clock pulse for I2C communication between the sensor and the microprocessor.
• Pin-4 – SDA-is the Serial Data Address. This pin is used by I2C communication to transfer the data from the sensor to the microcontroller.
• Pin-5- ADDR- is the Device Address Pin. This pin is used when more than one module are connected, for selecting the address.

There is another pin DVI which is the bus reference voltage terminal of the I2C module. It is also used as an Asynchronous reset terminal. After Vcc is applied DVI should be set to power-down mode. The IC may not function properly if this reset terminal is not set after applying Vcc.

Specifications

BH1750 is a 16-bit serial output type digital Ambient light sensor. Some of the specifications of this sensor are as follows-

• The power supply needed for the proper working of this sensor is 2.4V -3.6V.
• This sensor consumes a very less current of 0.12mA.
• No other calculations are required to measure the intensity of light, direct digital values are given to the microprocessor.
• This sensor has an ADC to convert analog light intensity to digital LUX values.
• BH1750 can measure light intensity up to the range of  65535 lx units.
• This sensor uses the I2C communication protocol to send data to the microprocessor.
• BH1750FVI is the main module present in the sensor. This module works on 3.3V. So, a voltage regulator is used with the IC.
• IR radiation has very less effect on the measurements of this sensor.
• BH1750 does not depend on the light source used.
• BH1750 has a 50Hz/60Hz Light noise rejection function.
• The measurement range of the sensor is adjustable.
• BH1750 has a very small measurement variation. It has a variation factor of about +/- 20%.
• The operating temperature range of this sensor is from -40°C to 85°C.
• The minimum I2C reference voltage is 1.65V.
• This sensor works with a 400kHz of I2C clock frequency.

Applications of BH1750

Ambient light sensors became popular in 2004 when they were used in cell phones. By 2004, 30% of the cell phones used in Europe contained an ambient light sensor, which increased to 85% by 2016. Some of the applications of ambient light sensors are listed below-

• These are used in pulse sensors to measure the light intensity of the LED.
• Cell phones contain BH1750 to adjust the brightness of the screen according to the external light conditions.
• Used in vehicles to turn ON/OFF the headlights according to the darkness.
• BH1750 is also used to control the turning ON/OFF of the automatic street lights.
• BH1750 is used to adjust the keyboard backlight in smartphones.

Alternative IC

Some of the Ic that can be used as an alternative to BH1750 are TSL2561, VEML6035. Some of the other types of light sensors are the LDR sensor and TCS3200.

Nowadays BH1750 is highly used for applications such as  LCD displays, Note PC, Portable game consoles, Digital camera, PDA, LCD TV, etc… to provide high user experience to the customer. Further details on the electrical characteristics of this sensor can be found in its datasheet. Which of the measurement modes of BH1750 has a high noise rejection factor?