High precision analog light sensor

Pandi March 9, 2015 3 min read

To measure the amount of light present and intensity of light presented, we decided to create light sensor but we simply didn’t want to create light sensor based on simple solution like change in resistance to measure the light .To provide a customer high precision light sensor we were looking solution in the form of IC’s and instead of measuring change in resistance we look into real solution to measure voltage or current directly. We found out the solution in the name OPT101 IC from Texas Instruments. So we decided to bring out this as the breakout with fixed and variable gain in single breakout in the name High Precision Analog Light Sensor.

Now we see briefly discuss what is OPT101 and How it would be used in high precision light sensor?

OPT101 is the monolithic photodiode with on chip transimpedance amplifier. In this IC output voltage is linearly proportional to light intensity. The integrated combination of photodiode and transimpedance amplifier on a single chip eliminates the problems commonly encountered in discrete designs such as leakage current errors, noise pick up and gain peaking due to stray capacitance.

Now we see power criteria, its operating voltage is from +2.7V to 36V.Since it operating voltage is from +2.7V to 36V we don’t need separate sensor for measuring high intensity light in high end applications. Now some questions arises in our mind whether it is suitable for battery operated equipment answer is absolutely yes since it’s quiescent current is only 120uA.It has the high Responsivity of 0.45 A/W(650nM) and the bandwidth is 14 KHZ. The output is 7.5mV when there is no light i.e dark current present.

In this IC there is one more option available we can also change the Responsivity and bandwidth by adding external resistor and capacitor which is included High precision Analog Light sensor breakout.

Here the tabular column represents the Resistor and capacitor values to be used for changing Responsivity and bandwidth,

Now we discuss some of the few applications done by using this breakout,

Measuring light intensity.
Differential light measurement.
LED output regulation by comparing two different light sources.
LUX meter by proper calibration.
Optical Communication.
Measuring various wavelength’s of light.

Test results:

We tested our breakout by illuminating a LED and programming it through Arduino with various time delay that too by delayMicroseconds and tested with CRO.

Arduino program:

When delay is 25uS,

When delay is 50uS,

When delay is 500uS,

Now we show how precision is this sensor by sending serial character by Arduino to the High Precision Analog Light Sensor breakout and captured the data with CRO. Here see the results,

Arduino Program: