OPT101 photodiode for plc input

Discussion in 'The Projects Forum' started by TDUKE02, Sep 30, 2015.

  1. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    My goal is to use the OPT101 chip combined with a 650nm laser for a "trip wire" going to an input on a micrologix plc. I have been having some issues getting an output voltage from the chip. I have the chip connected as follows.

    +Vs of 12v to pin 1(Vs)
    -Vs to pin 3(-Vs)
    jumper from pin 4(1M ohm feedback) to pin 5(output)
    volt meter across pins 8(common) and 5(output). (the meter only reads .4v when laser is shining or .2v without it.)

    If i jumper pin 8(common) to pin 3(-Vs) since they are both my "ground" i get the full 12v on the voltmeter regardless of the laser shining or not.

    any help would be appreciated. I am at a stand still.

    Thanks,

    Tim.
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Hi,
    Have you seen this application PDF for the OPT101.?
    It may help.

    At 650nm the response curve is about 75% of maximum at 850nm.

    What range/distance is your fence coverage and the IR emitter power.

    E
     
  3. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    I have not seen that pdf. I am using a 650nm 5mW laser diode and it is only about 6" from the photodiode. I would have gone to IR but wanted it visible for demonstrations. this is a school project and is supposed to show something relating to semiconductors we had learned.
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    OK.
    How are you screening the detector from ambient light.?
    Are you able to add the extra circuit amp as shown in the application PDF.?

    I assume at 650nm you can visibly see the beam hitting the detector.??

    E
     
  5. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    I have a small tube made of electrical tape that extends up about 3/4" to reduce the ambiant light snd to allow the laser to enter, and yes the laser can be seen hitting the chip. yes i can add anything else that is required to make it function.
     
  6. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Do you have a higher value feedback resistor, greater than the 1meg, say a 10meg, this will increase the gain by ~ 5 times to 11
     
  7. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    Ya I will plan on trying some other resistors to see the effects. As far as how I have the chip wired, do you think that is correct or is there a better way to do it?
     
  8. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Your OPT101 is wired as a datasheet example circuit, which should be OK for a simple test.

    Recheck your wiring just to be double sure that it is correct.
    For testing try moving the Laser closer to the OPT.
    Also if you have an oscilloscope connect that to the output of the OPT circuit, quickly move your hand between the Laser beam and OPT, watch the scope trace for any signs of a change.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If just demonstrating a simple photo cell input to a PLC digital I/O I would have though a simple visible light cell would have done the trick? it probably would be simpler to implement than one intended specifically for a linear reading?
    Sensitivity would be simple using a LM311 etc.
    Max.
     
  10. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    You're correct there is probably an easier way to do this. I had goofled pgotodiode amplifier and that is what seemed most popular. How would you reccomend I go about this then? im new to this stuff.
     
  11. MaxHeadRoom

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    Jul 18, 2013
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  12. TDUKE02

    Thread Starter New Member

    Sep 30, 2015
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    Awesome. Thanks for your help. I used a 741 op amp with 12v on the rails. two 10k resistors to divide the voltage for the inverting input and my photoresistor and a 3k resistor to adjust sensitivity on my non-inverting input. 100 ohm in series with my output to plc. works great with a 650nm laser.
     
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