Purpose of Modulation frequency of 5KHz on CN0312 and CN0363 Evaluation Borads

Hi,

I am using CN0312 Evaluation board to measure the absorption characteristics of different samples.

My question is why is there a need of modulation frequency for the LED i.e. 5KHZ or any other frequency on CN0312 and also CN0363.

The reason why i am confused is because there is no option for changing duty cycle in the software which could have allowed us to change the LED's brightness.

So, if we are not changing LED's brightness then what is the purpose of just modulation  for this specific application and why didn't you used just normal non-modulated dc source for this purpose?

Does it have anything to do with the Photodiode used in the board? Because I couldn't find anything conclusive.

Thanks in advance.

Regards,

Umer

Parents
  • +1
    •  Analog Employees 
    on Jul 22, 2019 12:48 AM

    Hi Umer,

    The modulation of light from the LED is used for ambient light rejection. By only detecting light modulated at a particular frequency, light coming from other sources are rejected. This reduces noise in the signal received by the photodiode using digital synchronous detection.

    Regards,

    Nikko

Reply
  • +1
    •  Analog Employees 
    on Jul 22, 2019 12:48 AM

    Hi Umer,

    The modulation of light from the LED is used for ambient light rejection. By only detecting light modulated at a particular frequency, light coming from other sources are rejected. This reduces noise in the signal received by the photodiode using digital synchronous detection.

    Regards,

    Nikko

Children
  • Hi Nikko,

    Thanks for the answer. So this means that even if we don't cover our system to protect it from random lights from outside it is good to go or we still need to properly cover it in a box or something?

    Regards,

    Umer

  • 0
    •  Analog Employees 
    on Jul 22, 2019 8:36 AM in reply to umer

    Hi Umer,

    Synchronous detection makes the system's noise performance better when compared to dc measurements. For the CN0363, this further increases when you use frequencies which aren't close to the frequency of other light sources.

    Yes, the system will still have good performance in the presence of random ambient light. However, covering it with a box will much more strongly ensure that possible random light sources close to the modulation frequency will have negligible effect to the measurement.

    By the way, in what environment and application are you using the boards?

    Regards,

    Nikko

  • Hi Nikko,

    Thanks for reply. I am using CN0312 as a reference system for Soil Nutrients Analysis, Nitrate and Phosphate concentrations mainly. The samples develop from light yellow to reddish colour as concentration increases. So, I am studying the absorption and comparing them with some custom designed Colorimeter Chambers as well as some Colour Sensors. I also bought CN0363 but haven't tested it yet.

    Regards,

    Umer