OPT101 and switching on a +5v

Discussion in 'The Projects Forum' started by purpleidea, Sep 7, 2007.

  1. purpleidea

    Thread Starter New Member

    Sep 7, 2007
    Hi, I've been tinkering and attempting to setup a laser-diode which hits a monolithic photodiode with op-amp, built in (opt101) and then use this small signal to open a +5v signal to an optoisolator which my pic reads.
    i'm not sure if i'm setting something up wrong with the opt101 or with the transistors afterwards but its not working well.
    at the moment, when i shine the laser on the opto, i see a potential difference of ~0.45v between the output pin and the positive+. i'm trying to either get this to open up the +5, directly or first use a common-emitter to amplify it to something that will make the second transistor happy. it's all going wrong, and my guess is that it may be related to the fact that the output potential is between that pin, and + as opposed to ground (which when measured with respect to output pin you see ~ 0.45+5v)
    thanks in advance, any circuit diagrams would be much appreciated.

  2. hgmjr


    Jan 28, 2005
    It would be helpful to have a sketch of the circuit you have at the moment. Can you please post one?
    If you don't have a schematic then we will need the part number of the component(s) you are using so that we can attempt to get a copy of the datasheet(s).

  3. Distort10n

    Active Member

    Dec 25, 2006
    OPT101 is a transimpedance amplifier. You say you meansure an output that is 45mV lower than the V+ (positive supply)? Then that looks like it is ok to me. The high voltage output swing is Vs-1.3V typical, so you are seeing excellent response.
  4. purpleidea

    Thread Starter New Member

    Sep 7, 2007
    hey thanks for the replies... i'm sure that the opt101 (transimpedance amp) is working well, it's that i don't know how to take it the next step. i tried fiddling with a common emitter setup to get the 45mv up to something high enough to switch a transistor (about 0.7v i think is what is required) and other transistor amps, and i've had little success. i was hoping someone could give me a circuit diagram and or some guidance on how to use this 45mv output to drive a +5v circuit to close. (transistor switching style i would suppose...)

    thanks again!

    ps: any link in google for opt101 should send you to the right specs. i've got it wired with a +5 supply, in the "basic circuit connection"