Interfacing TSL25911 Ambient Light Sensor with Arduino

Detecting the amount of light in the ambiance is necessary for many areas of our everyday life, and the sensors which can do this are called light sensors, the most primitive light sensor is a humble LDR. But you can find much more advanced types of light sensors being used in automatic lighting systems for smartphones and other smart devices. The perfect example of such a scenario is the auto-brightness control of our smartphones or laptops.  The amount of light is measured by such devices and the screen brightness is adjusted proportionally to the ambient light. This avoids having the screen be too bright when the user's pupils are adapted for vision in a dark room, or too dim when the device is used outdoors in the daytime. Dimming the screen on a mobile device also prolongs the lifetime of the battery. So, in this Arduino interfacing tutorial series let’s look at such a sensor module built around the TSL25911 light sensor.

TSL25911 Ambient Light Sensor Module

This is a high-sensitivity digital ambient light sensor module based on the TSL25911fn chip from ams. It can sense the ambient light intensity around and output it through the I2C interface. The output data uses a formula to derive the illuminance in lux (ambient light intensity) to approximate the human eye response. We have previously used the BH1750 with Arduino which can also measure light intensity in LUX, you can check it out if you are interested. 

Features

• Adopts TSL25911FN, measures infrared plus visible light.
• Embedded ADC, direct light intensity signal output to I2C interface, less noise jamming.
• High sensitivity up to 188uLux, wide dynamic range up to 600M:1.
• Embedded infrared-responding photodiode allows precise measuring even in a strong infrared noise environment.
• Provides interrupt output with programmable upper and lower thresholds.
• Onboard voltage translator, compatible with 3.3V/5V operating voltage.

TSL25911 Sensor Module Pinout

The TSL25911 sensor module has a total of 5 pins. Two power pins, one interrupt pin, and two I2C pins. The pinout of the module is as follows:

VCC - Provides power for the module, Connect to the 5V pin of the Arduino.

GND - Ground Connected to Ground pin of the Arduino.

SCL -Serial Clock Used for providing clock pulse for I2C Communication.

SDA - Serial Data Used for transferring Data through I2C communication.

INT – Interrupt Pin.

TSL25911 Sensor Module Parts

The TSL25911 sensor module has only very few components, which include the TSL25911FN AMS chip itself along with the voltage regulator and the level shifter circuit. You can also find multiple bypass capacitors used to eliminate any noise in the supply.

Commonly Asked Questions

What is the sensitivity of the TSL25911 sensor?

The TSL25911 sensor has a sensitivity of 188µLux.

What are the main benefits of the TSL25911 sensor over other light sensors?

• Design flexibility for dark glass and placement
• Enables operation in IR light environments
• Enables dark room to sunlight operation
• Reduces microprocessor interrupt overhead
• Improves lux accuracy across various light sources

Where are Ambient light sensors used?

The Ambient light sensors are used, wherever there is a need to measure the light intensity. Some everyday products use such sensors including smartphones, laptops, smart watches, etc.

TSL25911 Sensor Module Circuit Diagram

The schematic diagram for the TSL25911 sensor module is given below. As mentioned earlier, the board has a very low component count. The main components are the TSL25911 chip and the voltage regulator along with the level shifter circuit.

For generating 3.3V for the TSL25911, the RT9193-33 LDO is used. This low drop-out regulator from Richtek is capable of delivering the current up to 300mA. The RT9193 performance is optimized for battery-powered systems to deliver ultra-low noise and low quiescent current. A noise bypass pin is available for further reduction of output noise.

The level shifter circuit is built around the NDC7002N dual N-Channel MOSFET. This level shifter circuit enables us to use the module with 5V systems and microcontrollers. You can also find many bypass capacitors on board which are used to reduce the power supply noise.

How does the TSL25911 Sensor Module Works?

The TSL25911 contains two integrating analog-to-digital converters (ADC) that integrate currents from two photodiodes. Integration of both channels occurs simultaneously. Upon completion of the conversion cycle, the conversion result is transferred to the Channel 0 and Channel 1 data registers, respectively. The transfers are double buffered to ensure that the integrity of the data is maintained. After the transfer, the device automatically begins the next integration cycle. No external circuitry is required for signal conditioning. Because the output of the device is digital, the output is effectively immune to noise when compared to an analog signal.

The TSL2591 also supports an interrupt feature that simplifies and improves system efficiency by eliminating the need to poll a sensor for a light intensity value. The primary purpose of the interrupt function is to detect a meaningful change in light intensity. The concept of a meaningful change can be defined by the user both in terms of light intensity and time, or persistence, of that change in intensity. The device has the ability to define two sets of thresholds, both above and below the current light level. An interrupt is generated when the value of conversion exceeds either of these limits. One set of thresholds can be configured to trigger an interrupt only when the ambient light exceeds them for a configurable amount of time (persistence) while the other set can be configured to trigger an immediate interrupt. The below image shows the internal architecture of the TSL25911 sensor chip.

Circuit Diagram for Interfacing TSL25911 with Arduino

Now that we have completely understood how a TSL25911 ambient light sensor works, we can connect all the required wires to Arduino and write the code to get all the data out from the sensor. The following image shows the circuit diagram for interfacing the TSL25911 ambient light sensor module with Arduino.

 

Connections are pretty simple and only require 4 wires. Connect the VCC and GND of the module to the 5V and GND pins of the Arduino. Then connect the SDA and SCL pins to the Arduino’s A4 and A5 respectively. Here's how the real-life connection looks.

Arduino Code for Interfacing TSL25911 Sensor Module

Once the connections are made, download the code provided in the GitHub link at the bottom of this page, and extract the sketch file along with all the library files needed. Compile the code and upload it to Arduino. The code will print out the sensor reading to the serial monitor.

#include "DEV_Config.h"
#include "TSL2591.h"
UWORD Lux = 0;
void setup() {
  DEV_ModuleInit();
  Serial.print("TSL2591_Init\r\n");
  TSL2591_Init();
}

First, we have included the header files for the TSL2591 library. After that, in the setup function, we initialized the sensor by calling DEV_ModuleInit() function. The serial port at a baud was initialized with ion the DEV_ModuleInit() function. So that we don’t have to initialize it in the setup function.

void loop() {
    Lux = TSL2591_Read_Lux();
    Serial.print("Lux = ");
    Serial.print(Lux);
    Serial.print("\r\n");
    TSL2591_SET_LuxInterrupt(50,200);
}

In the Loop function, we will continuously read the sensor data and will print it to the serial monitor. The below video shows the TSL25911 sensor interface in action.

Supporting Files