TSL251R Light to Voltage Converter

Description

Note:  This part is obsolete and no longer available.

The TSL251R Light to Voltage Converter is a precision device that converts visible light to an analog voltage that is directly proportional to the intensity of light that is falling on the device.

PACKAGE INCLUDES:

• TSL251R Light to Voltage Converter

KEY FEATURES OF TSL251R LIGHT TO VOLTAGE CONVERTER:

• High visible light sensitivity form 400nm to 700nm
• Quick reacting
• Analog output proportional to the intensity of light falling on the detector
• 3.3 and 5V compatible

The TSL251R is highly sensitive to changes in visible light in the range of 400-700nm and is quick reacting with a 70uS rise time.  The output is an analog voltage that is directly proportional to the light intensity falling on the device.

It is highly sensitive to changes in the visible light in the range of 400nm to 700nm and is  quick reacting with a 70uS rise time.

The package is a ‘side-looker’ type that incorporates both a photodiode and transimpedance amplifier.

The device can operate over a power supply range of 2.7 to 5.5V. With a typical supply voltage of 5V, the output voltage will range from approximately 10mV under full dark conditions to around 3.8V under intense illumination.

OUR EVALUATION RESULTS:

These are much more capable devices than a LDR type device when it comes to sensitivity and speed and are therefore good for more demanding light detection applications.

One thing to be aware of is that because the device is very fast reacting, it will react to the fluctuating brightness of lights such as incandescent and fluorescent that fluctuate in brightness from the AC power lines at a 60/120hz rate. If that is an issue for your application, a simple RC filter can be added to the output of the device to filter out most of this flicker.

Below are scope captures of the output with a fluorescent light nearby. The first is with the raw sensor output which shows a 300mV ripple.  The second is with an RC filter added to the output comprised of a 10K load resistor and 10uF filter capacitor as shown in the diagram below which reduces the ripple to < 10mV.  These are both taken with the scope set to 100mV / Div and AC coupled.

TSL251 Scope Capture – No Output Filter

TSL251 Scope Capture – With Output Filter

Filtering will slow down the response time of the sensor to light changes, so that should be kept in mind if a very fast response time is desired.  The resistor and capacitor values can be played with to adjust the response time if that is an issue for the application.

The program below simply reads the output of the sensor every second and prints it to the Serial Monitor window.

The sensor is connected to analog pin A0, but this can be changed to any convenient analog input.   Also be sure to provide power and ground.

TSL251R Light To Voltage Converter Example Program

/*
Light Sensor Module Test

Basic code for reading the analog output of the light sensor
*/
#define ANALOG_PIN A0    // Set to any available analog input pin
int rawValue = 0;       // Returned ADC reading from sensor
//===============================================================================
//  Initialization
//===============================================================================
void setup() 
{ 
  pinMode (ANALOG_PIN, INPUT); // Set pin for input
  Serial.begin(9600);          // Set comm speed for debug window messages
}
//===============================================================================
//  Main
//===============================================================================
void loop() 
{
  rawValue = analogRead (ANALOG_PIN);  // Read sensor input and print out
  Serial.print ("Reading Raw Sensor Data: ");
  Serial.println (rawValue);
  delay (1000);
}

Notes: 

1. None

Technical Specifications

FURTHER READING