OPT3007 Ultra -Thin Ambient Light Sensor

Light is responsible for our sense of sight. The word light refers to the visible light spectrum, which is a part of electromagnetic radiation. Among all other spectrums of electromagnetic radiation, humans can see only the visible light spectrum. The wavelength of visible light is from 400nm to 700nm. An ambient light sensor is a device that is used to measure this visible light. This sensor is usually found in smartphones and other mobile devices. This sensor is applied to control the lighting conditions of the devices. Ambient light sensors are of three types- Photodiode, phototransistors, and photonic integrated circuits. Photonic IC contains both phototransistors and an amplifier on one device. One of such IC is OPT3007.

What is an OPT3007 IC?

OPT3007 is an Ultra-thin Ambient light sensor that can measure the intensity of visible light. This sensor can be easily interfaced with microcontrollers. The digital signals are passed using I2C and SMBus communication protocols.

This sensor contains infrared rejection which helps it to measure the light with a spectral response that matches the human eye. This sensor is not excessively sensitive to non-ideal particles and micro shadows.

To create ideal lighting experiences for humans, ambient light sensors are preferred over photodiodes and photoresistors. OPT3007 is capable of measuring light similar to human perception under high infrared lighting conditions such as halogen or sunlight sources.

Block Diagram of OPT3007

The sensor should measure the same spectrum of light that the human sees to create optical conditions that are optimal for humans. OPT3007 also has an infrared ray rejection to accurately represent the human experience.

For the given lighting condition, OPT3007 can automatically predict the optimal full-scale range with an automatic full-scale range setting feature.

Both I2C and SMBus interfaces are compatible with OPT3007. The two pins -SCL clock pin and SDA open-drain bidirectional data pin, are used to connect OPT3007 to the bus.

This sensor operates as a slave device for both I2C and SMBus. To communicate with the sensor, the master first initiates an I2C start command. Using a seven-bit slave address 1000101, the master addresses the slave device.

Circuit Diagram

In the circuit diagram, measurement of ambient light using OPT3007, which is mounted on a flexible PCB is described. Applications that require control as a function of ambient light use ambient light sensors. OPT3007 has two categories of interface- Electrical interface and optical interface.

I2C SDA and SCL pins are used to interface the sensor with a microcontroller. In an electrical interface, these SDA And SCL pins are connected to the same pin of the microcontroller. Pull-up resistors are connected between the power supply and SDA and SCL pins. To balance the speed, power, noise immunity, and other requirements, the resistor choice can be optimized.

To minimize the amount of coupling into the communication lines proper layout practices should be used. There are two ways in which noise can be introduced into the communication lines.

One way is from capacitively coupling signal edges between the two communication lines themselves and the other way is through switching noise sources present ion the system. When working in a noisy environment, shield the communication line to prevent the noise from entering into the system.

In the circuit, OPT3007 is mounted on a flexible PCB with a cutout that allows the light to illuminate the sensor. The dimensions and tolerance of this cutout can impact the optical-field-of-view performance of the system.

Field-of-view is the angle at which angular response is 50% of the maximum value of system response. The systems field of view depends on the axis of rotation.

Pin Description of OPT3007

OPT3007 is available as an ultra-small 6-pin Picostar package. The pin description of this IC is as below.

• A1 is the ground pin GND.
• B1 is the no connection pin NC.
• C1 is the power supply pin VDD. A voltage of 1.6V to 3.6V is supplied to this pin.
• A2 is the I2C clock pin SCL. It’s a digital input pin. This pin is connected to a voltage supply ranging from 1.6V to 5.5V through a 10-kΩ resistor.
• B2 pin is the no connection pin NC.
• C2 is the digital input/output pin SDA. It is the I2C data pin.  This pin is connected to the voltage supply through a 10-kΩ resistor.

Specifications of OPT3007

Specifications of OPT3007 ultra-thin ambient light sensor are as follows-

• OPT3007 is a lux meter that measures the intensity of visible light.
• The measurement range of this sensor is from 0.01 lux to 83k lux.
• This sensor has an automatic full-scale setting feature.
• 23-bit effective dynamic range with automatic gain ranging is also present in this sensor.
• This sensor works with a low operating current of 1.8µA.
• The operating temperature range of OPT3007 is from -40°C to 85°C.
• OPT3007 has fixed I2C addresses.
• This sensor has a wide power supply range from 1.6V to 3.6V.
• Precision optical filtering is present in this sensor to match the photopic response of the human eye.
• This sensor contains 5.5Vhandeld tolerant I/O.
• OPT3007 has a small form-factor.
• VDD to ground voltage supply for this IC is in the range of -0.5V to 6V.
• This sensor is available as an ultra-small Picostar package.

Applications

Applications of OPT3007 are as follows-

• Due to its ultra-small size, this sensor is used in smartwatches and wearable electronics.
• Cameras.
• Tablet and notebook computers.
• This sensor is used to control the display backlight.
• Lighting control systems also make use of this sensor.
• This sensor is also applied for health fitness bands.
• OPT3007 can be used as a replacement for photodiodes and photoresistors.

Alternative IC

Some of the IC that can be used as an alternative to OPT3007 are OPT3004, OPT3006, OPT3002, OPT301, etc…

OPT3007 is a thin wafer of active silicon. It does not contain any mechanical protection or reinforcement. So, this sensor should be handled with proper care. Keep the optical surface of the device clean of any fingerprints, duct, etc…

Further information on the electrical characteristics and functioning of the sensor can be found in the datasheet provided by Texas Instruments. What extra precautions have you taken while using this sensor?

Image Credits: Texas Instruments