The following is the circuit for Light communication using opt 101P photodiode.

enter image description here

Connections are COM pin (pin 8), and pin 3(-V) are grounded. Input volatge(pin 1) Vcc = 9 V . OPT 101 has a photodiode and a transimpedance amplifier.

Here is the data sheet for opt 101P.

I have given proper connections according to the datasheet. But the problem here is opt 101P photodiode is not detecting the light.

If the photodiode is illuminated with light, small photocurrent produced is converted into the voltage by transimpedance amplifier at pin 5. But in my test, I didn't get any voltage at the output pin 5. Can anyone specify how to test opt101P photodiode?


closed as unclear what you're asking by Marcus Müller, Andy aka, Olin Lathrop, The Photon, Dave Tweed Nov 29 '16 at 18:14

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ How about a link to the data sheet? \$\endgroup\$ – Andy aka Nov 29 '16 at 10:30
  • \$\begingroup\$ ti.com/lit/ds/symlink/opt101.pdf \$\endgroup\$ – Veena Nov 29 '16 at 10:32
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    \$\begingroup\$ Also, this looks like a very fundamental question – you have the data sheet, thus you should be able to know what you should be seeing on the device's output. The fact that you're asking how to test the thing points to you not being versed with basic electronics – so if we had to write an answer for you, we'd need to start with Adam and Eve. It's thus absolutely necessary to include what you've done, including your schematic, and then explain what "is not detecting" means to you. \$\endgroup\$ – Marcus Müller Nov 29 '16 at 10:34
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    \$\begingroup\$ And, to add to the above, the big suspicion from the guys here (and hopefully I'm speaking for them) is that you HAVE NOT wired it up as per the data sheet THEREFORE you must show what you have done and not point at a data sheet (again). It's just plain bloody rude to do that. \$\endgroup\$ – Andy aka Nov 29 '16 at 10:38
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    \$\begingroup\$ It's been half an hour. Voting to close as unclear. \$\endgroup\$ – Marcus Müller Nov 29 '16 at 10:58

You are trying to feed an AC coupled signal into an OPAMP circuit (LM324) that is powered from a single rail. At best, you might recover a half rectified signal because the common-mode input range for an LM324 is not specified to be lower than 0V.

At worse, you might see no signal at all because of the input offset voltage of the LM324. I also see NO power supply decoupling on the LM324 or photodiode chip and I'm pretty sure these will be recommended.

If the photodiode is illuminated with light,small photocurrent produced is converted into voltage by transimpedance amplifier at pin 5.But in my test, I am not get any voltage at the output pin

This will produce a DC voltage at the output of the OPT101 and, apart from a small transient as you switch on the illuminations, capacitor C1 (4.7 nF) will block that DC voltage from sending any further signal to the badly-connected (or badly powered) op-amp. What can you expect with an AC coupled amplifier?

  • \$\begingroup\$ I'm usually really not of the vengeful kind, but in this case, I think it'd be both more helpful for the overal EE.SE quality as well as for OP to leave them sit with their problem until they brought their question into a clear shape. By the way, fully agreeing; the CR highpass between OPT thing and the external opamp has a >1kHz cut-off, so OP wouldn't even see what's happening in a properly biased setup. \$\endgroup\$ – Marcus Müller Nov 29 '16 at 12:32

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