• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 31 subscribers
  • Views 1398 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

photo-diodes and spectral sensitivuty

Deepak%20murali
Expert 1095 points
Other Parts Discussed in Thread: DDC112, OPT101

Hi,

    I wanted to pass light from LED's(at least 5 LED's of different wavelength) through a sample and study by how each wavelength will get observed by that sample. All the LED's will emit light in visible range. To detect the amount absorbed I am planning to use photodiodes.

But I think frequency response(by 'frequency', here I mean the frequency of light incident on the photodiode) of any photodiode will not be even. I mean , for a given photodiode the current output for different wavelength(but same intensity) will be different.

How to overcome this problem? Do I have to use different photodiodes(of peak sensitivity at different wavelength) or is there any other better way.

Also I want a solution which I can implement in Breadboard.

Actually I want to study the absorption effect of different wavelength when passed through blood sample(blood will be collected inside a test tube). It is some thing like 'pulse oximetry'

Can any one help?

  • 0
    Expert 1095 points

    Hi,

    I think I can proceed like comparing the output current with/without the sample. 

  • 0 in reply to Deepak%20murali
    TI__Genius 14825 points

    Deepak,

    I'm not terribly familiar with photodiodes in the visible light spectrum but for your application, you might try hooking up a photodiode to a DDC112 (assuming the currents fall within one of the measurable ranges of the DDC112) and measuring the current that way.  The DDC family of devices are intended to measure photodiode current so it may be a good fit for your project.

    You might also review this page: http://www.ti.com/lsds/ti/analog/webench/sensors-photodiode.page as it is a webench photodiode application with a list of photodiode vendors at the bottom to help you get started.

    Jason Bridgmon

  • 0 in reply to Jason Bridgmon
    TI__Expert 6930 points

    Hi,

    Another option and super simple and easy to breadboard with is OPT101...it has the photodiode already itegrated into the device along with single supply transimpedance amplifier and 1Meg Ohm feedback resistor.  A typical application for the The OPT101 is in blood analysis equipment wherein light from an LED is either passed through or reflected from a blood sample.

  • 0 in reply to Jason Bridgmon
    Expert 1095 points

    Hi Jason Bridgmon,

    Thank you for your reply. But can DDC112 be used in bread board? Is it available in DIP package? I have seen IC's manufactured in many packages. How(From where) do I find what type of package it is? Most of the time I wanted to know whether I can use it in bread board or not. Please help me. 

  • 0 in reply to Deepak%20murali
    TI__Genius 14825 points

    Deepak,

    The DDC112U or UK option are the biggest packages in the DDC line with leads, as opposed to most of the other DDC products which are in leadless packages.  However they are not DIP compatible and would require some soldering and interfacing to use in a breadboard.

    Jason Bridgmon

  • 0 in reply to Jason Bridgmon
    Expert 1095 points

    Hi Jason Bridgmon,

      Thank you for your reply. Can I use the internal ADC of  MSP430 microcontroller along with the photodiode circuit(OPT10) as I want DIP package only?

  • 0 in reply to Deepak%20murali
    TI__Genius 14825 points

    Deepak,

    The OPT101 will output voltages up to Vsupply-1.3V.  The MSP430 1-series has a 12bit ADC that measures between VREF- and VREF+, and the easiest way to hook that up is to use the internal 2.5V reference for Vref+ and ground for Vref-.  If your supply is 3.6V (max for the MSP430 1-series) and you use the same 3.6V supply for the OPT101, you would have 3.6-1.3 = 2.3V of OPT101 output swing, which is less than 2.5V so it shouldn't rail.

    The only thing left for you to do is make sure the OPT101 expected output swings between 0 and 2.3V in response to your input signal.  See figure 4b of the OPT101 data sheet to see how to adjust the DC Gain of the OPT101 using external feedback resistors in parallel with the internal 1Mohm resistor.  http://www.ti.com/lit/ds/symlink/opt101.pdf

    I hope this helps your project.


    Jason Bridgmon