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    Photo diode with basic circuit

    Hi,

    I am working on one of the project of laser i am selcted a laser diode module whose configuration is 670nm,3mm beam width .
    I want to detect that laser beam within a particular time .My laser module is rotates at 600rpm.

    For detect a laser light which is red we decided to use below photo diode.

    http://www.farnell.com/datasheets/57173.pdf

    But i am little confused about selection of circuit of receiver side.

    There are so much different basic circuit like only using resistor,or transistor with bias or without bias or using differential op-amp.
    So which one i select that i am confused, because accordingly my output of photo diode i have to change in output of micro controller.

    So please suggest me which one is reliable in my condition.

    Thank You,

    •   Alt29th October 2011, 10:33

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    Re: Photo diode with basic circuit

    Yes there is a great variety of configurations to try.

    Some circuits are better at amplifying current, some better at amplifying voltage, some are more sensitive, some respond more quickly, some generate pulses, some duplicate the waveform in the lightbeam, etc.

    Photodetectors don't all have the same characteristics. So there can be more than one circuit that will work with your photodetector.

    It depends on what works best with your photodetector characteristics, and the strength of signal it is receiving, and the ambient light conditions.

    Which conditioning circuit to use will also depend on what you want the output to be like, as based on the next stage in your circuitry.

    It all adds up to having to experiment. Start with what's easy and see if it's sufficient.

    With a laser beam hitting the photodiode there's a chance you will get a strong enough response that you'll need little or no amplification. However you don't normally connect the photodiode directly to the next stage.

    Start with a resistor above or below the diode. Tap between them and see what voltage you get when a beam hits it as compared with no beam.

    If you get the wrong polarity then turn the diode upside-down. Etc.

    If you need amplification: Try the diode connected in series with a transistor bias (not the most typical configuration, but you're just experimenting). Put a potentiometer in series set to high resistance to start with so you don't ruin the transistor. See if the diode produces sufficient current to turn on the transistor.

    Turn the diode around if necessary. Reduce with the potentiometer if necessary. Or add more bias from an additional resistor network if necessary. Etc.

    Or you can set the diode to bias the transistor in the conventional common-emitter configuration, etc.

    Or set the diode in the emitter leg of the transistor and use common-base configuration, etc.

    All depending on what voltage and current you are getting from the diode, and depending on what you need going into your next state.


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    Re: Photo diode with basic circuit

    hi,

    Thanks for reply me.....

    As you said to connect photo diode with resistor and measure voltage across it when laser light ray falls on photo diode..

    I will do it with both possibility.

    I want to know that if i will use a photo transistor instead of photo diode than it will reliable or not..& for it same circuit i will used for testing ????

    Please guide me for this.

    Thank you.



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    Re: Photo diode with basic circuit

    The two are different in that the photodiode produces a small current/voltage when light falls on it. You can measure it directly with a meter or oscilloscope. (That is, the few photodiodes I've worked with.)

    A phototransistor reduces its own internal resistance when light falls on it. This is the one where you normally attach a resistor, and tap in between them. You may find this is satisfactory depending on the brightness and timelength of pulse from your laser beam. (I don't know if a laser will damage it.)

    A photodiode ordinarily has a faster response time than a phototransistor. Hence it may work better with your rotating laser setup.

    A photodiode also is a bigger target for a laser beam. (Or maybe you plan to put up a translucent scatter-shield just in front of your photodetector?)

    The method used for a phototransistor may work for the photodiode in many cases. However you may instead find it is confounding that method with its own contribution of voltage and/or current and /or change in resistance.

    What this adds up to is, photodiodes are unusual in their behavior and are not the most routine kind of component to work with. So we see various circuits for amplifying a signal from one.

    It's best to take such circuits as a starting point to work from. Each took some effort to adapt to a component's operating characteristics. To adapt your component is going to take some effort as well.

    The proper way to amplify the signal also depends on ambient light conditions, and what sort of light-borne signal you're detecting. If there is light-noise hitting the detector, then too much amplification will give you false triggers. Etc.

    Millivolts can make a difference.

    In any case whether you use a transistor or op amp...

    The key is to adjust both the gain and the threshold of operation, until your output shows that enormous change in voltage between (a) idle and (b) signal.

    Experimenting is crucial in order to persuade your raw detector to give you this.

    You may have success with the first circuit you try.



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    Re: Photo diode with basic circuit

    Hi,

    I done this Experiment with single Resistor without power supply given to the Photo Diode.
    And in this Experiment i get 300mv when R =10 ohm When light is not fall on Photo diode

    & when IR led's Light falls on it that time output voltage id 155 mv.

    now i am going to test this with laser module which is 670nm laser beam.

    This all first i done without power supply.and then i will give a reverse voltage to photo diode and then above experiment i will do with this configuration.

    So please guide em for this.

    Thank You.



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    Re: Photo diode with basic circuit

    Yes you are on the right track. (Although I don't know how you got the diode to produce higher voltage with less illumination.)

    Alert: Do not hook it up to a power supply unless you also put a sufficiently high resistance inline. Say 1000 ohms.

    Overmuch current can ruin the diode. Can you find how much the spec sheet says is a maximum safe amount?

    As you can see its range of operation is just a few tenths of a volt.

    Your amplifier will have to respond to this small signal. It will need to respond quickly. An op amp might be easy to use, however it may or may not respond quickly enough to your signal.

    A transistor circuit is likely to work well. Possibly using a microwave transistor or other quick-response type. If you can find the best configuration to amplify.



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    Re: Photo diode with basic circuit

    hi bradrherad,

    Thanks For Reply me,As you told for active area of the photo diode ,it is 0.13mm2.
    I am also done this with laser diode that time output voltage is 30mV,56mV,i got when laser light falls on it.
    But when reverse bias voltage i gave that time the out put across the saturation current was 11.3
    & when IR light falls on it its output was 8.6mV & when laser light falls on it its increased to 13.2mV.

    I think i done some thing wrong in reverse polarity conflagration.

    As you say i am going to try it with 1kohm resistor .

    And also with LM741 Op-amp.

    If you know proper circuit configuration than guide me for this experiment.

    Please guide me for this,

    Thank you

    ---------- Post added at 10:56 ---------- Previous post was at 10:56 ----------

    hi bradrherad,

    Thanks For Reply me,As you told for active area of the photo diode ,it is 0.13mm2.
    I am also done this with laser diode that time output voltage is 30mV,56mV,i got when laser light falls on it.
    But when reverse bias voltage i gave that time the out put across the saturation current was 11.3
    & when IR light falls on it its output was 8.6mV & when laser light falls on it its increased to 13.2mV.

    I think i done some thing wrong in reverse polarity conflagration.

    As you say i am going to try it with 1kohm resistor .

    And also with LM741 Op-amp.

    If you know proper circuit configuration than guide me for this experiment.

    Please guide me for this,

    Thank you



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    Re: Photo diode with basic circuit

    Typical use of a photodiode with an op amp is simply to connect it across the differential inputs. This may work for you.

    However there's a very important factor: keep in mind how long the laser illuminates the diode. Is it a millionth of a second? A billionth? Your amplifier must respond quickly enough to generate a pulse. It must have a fast enough slew rate. Op amps vary in this spec. An op amp contains several transistors. Each transistor introduces a propagation delay.

    Be surprised if you can find an op amp that responds in less time than one transistor can.

    Is it correct to say your experiments are producing disjointed results? Some of your readings seem inexplicable. Can you repeat the initial higher readings? If not then the diode's operating characteristics may have deteriorated.

    All this is part of what electronics is about.

    One concept to be aware of is: how much you should 'pre-bias' the diode. You may have to apply a certain amount of voltage/current in the quiescent state, in order to push it to a position along its response curve where it will yield the maximum output spike when the laser falls on it.

    Think of this as 'taking up slack in the gears'. It's so that the junction capacitance (40pF) won't cause so much of a delay in the response. Or it's so you need minimal additional bias to turn on any pn junctions in the following stage of your amplifier (whatever type of amplifier you use).

    Therefore you should test the photodiode with various supply voltages. (You probably don't need to pre-bias it over 0.7 V.)

    And maybe various inline resistances. (But not so low as to admit overmuch current.)

    And with the laser on the diode versus ordinary room light.

    With the diode oriented one way. And with it oriented in the opposite direction.
    Etc.

    It does seem like a lot of work. But to get the best performance out of the device, you need to be acquainted with its operating characteristics.

    The job is complicated by the fact that the photodiode produces DC voltage/current. It would be easier if it simply changed its resistance, like a cadmium sulfide photocell, or a phototransistor.

    You must figure out how to get this characteristic to work for you.



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    Re: Photo diode with basic circuit

    hi,

    Thanks for reply me.

    As you said i will try to give power supply of different value like 5V,3.3V,9V and measure its output.

    I also tried with op-amo LM741 ,Output of this experimnet is

    When laser light is not fall on photo diode,
    Voltage :46mV,44mV
    When laser light falls on photo diode,
    Voltage :17mV,9mV

    So please guide me for this.

    I also atteched some Picture which configuration i used







    •   Alt2nd November 2011, 06:37

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    Re: Photo diode with basic circuit

    Since no particular combination stands out, then it's time to try one of the amplifier configurations that worked for someone else.

    Below are some webpages showing circuits for hooking up a photodiode to an op amp. I don't think any two of them are identical. However several resemble each other.

    See if one resembles the circuits you have seen already. Try constructing the one that makes the greatest sense, which has clearly identifiable supply connections, input connections, etc.

    Some specifiy a particular op amp number. It's probably okay for you to use a 741 if that's what you have.

    LM359 Fast Photodiode Amplifier | Simple Circuit Diagram

    Light Sensor, Photocell and LDR Sensor

    Photodiode Technology

    Automated Timestamp for Computed Radiography

    Transimpedance Photodiode Amplifier

    Photocell Amplifiers - Freecircuits.net

    Op Amp Circuit: Op Amp Circuit of Photodiode Amplifier

    ELEC 242 Lab - Experiment 9.1

    Infra Red Remote Control Extender by CA3140| Circuit Project

    This one uses transistors:

    Buffers and Current Amplifiers



    •   Alt2nd November 2011, 09:34

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    Re: Photo diode with basic circuit

    also tried with op-amo LM741 ,Output of this experimnet is

    When laser light is not fall on photo diode,
    Voltage :46mV,44mV
    When laser light falls on photo diode,
    Voltage :17mV,9mV
    LM741 needs a dual supply to work in this circuit. The OP circuit should be better used with inverted photo diode polarity to achieve positive output and use a rail-to-rail OP to work with single supply.

    The original post refers to a rotating laser. Depending on the distance, the pulse width will be pretty short (e.g. 5 us @ 10 m), an OP should have sufficient speed to handle the signal. LM741 or simple rail-to-rail types like LM324 are too slow. They are O.K. on short distance, e.g. 1 m.


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    Re: Photo diode with basic circuit

    hi,

    As you said that LM324 or LM741 is not very useful for long distance to detect laser beam,So can you suggest any other op-amp which give high response time.

    As now i test it using LM339 which i given below



    But in this its LM339, R=1k & R=220E between first op-amp to second's i/p .I used below Photo diode.
    http://www.farnell.com/datasheets/57173.pdf

    Out put is like 25mv when light is not fall on Photo diode & 9mv when light fall on it.

    So please give me some guidance regarding this.



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    Re: Photo diode with basic circuit

    1.

    The LM339 is a comparator. It works slightly different from an op amp.

    It can work from a single supply. Its output pin gives you either hi-impedance or gives you a path to ground. You won't get a positive voltage from it. Take meter readings by putting your red lead on supply +V and your black lead on the output pin.

    The feedback path may work the same as for an op amp, or it may not.

    If you can't get more output voltage swing from the 339 then I recommend you go back to the 324 op amp. It will be easier to use while you're developing the project.

    For your final working design, you may find the 339 is faster.

    2.

    Try a higher value than 1K for R1 (feedback resistor). You need more gain.

    3.

    You should try all the possible ways to hook up the photodiode. You probably have seen that some circuits place the diode connected to V- instead of V+. Or across the inputs. Etc.

    One of these methods is bound to give you more voltage swing than the others.

    Also try reversing the diode polarity as well. Just in case.



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    Re: Photo diode with basic circuit

    hi,

    Thank you for giving me above suggestion.it is relay very help full for me.

    I am getting very good amplified output when i directly used 10 Mohm register in feedback.
    My output without Laser source was 2.2mv And when laser light falls on it it became 17mv.
    So now i get improved output using LM339.

    As you told to LM324, Its better then LM339.Using this LM324 I get better amplification up-to some volts from mV.

    So now i want to convert this mV to Digital Signal which i will give to some logic circuit.

    Please guide me for this.

    Thank You,.



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    Re: Photo diode with basic circuit

    Hi Henna123,

    I think better to use Photo-transistor like QT120 or simillar ....gives better light sensistivity as base current will get controlled by light....there is almost amplifacation factor ( beta) multipled by base current kind of range extention of the light levels....

    Milind



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    Re: Photo diode with basic circuit

    It's vital for you to obtain greater output voltage swing.

    The aim is to get the output to read zero V in room light, and 5 volts when the laser flashes it. (Or vice versa depending.)

    As long as you can get a few mV difference, then it should be possible for you to configure an op amp to amplify it several hundred times. Or two op amps as shown in your schematic.

    Did you try various experiments applying small signals to your op amp input, in order to check operation just by itself?

    Your post #7 reported 56 mV when you performed one test with the laser.

    And post #5 told about getting 300 mV in room light.

    Maybe the photodiode is no longer working as well as it did at the beginning?

    As you can see, a photodiode is more complicated to work with than a phototransistor. It may be worthwhile to try experimenting with a phototransistor as post #15 suggests.



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    Re: Photo diode with basic circuit

    hi all,

    my experiment is successfully completed done with photo diode & op-amp LM324.
    I got 2.45V after amplification .

    so now not a issue for this.

    Now i am going to detect this pulse using PIC micro controller as an Interrupt to do further process.

    This pulse is only have 1us time.

    i am using PIC18f46j11 for this with 20Mhz crystal.

    I wrote a program for this to detect the interrupt on PORT B Pin0,which already work as external interrupt.

    But my controller could not detect this pulse as a interrupt.

    then i think about pulse stretching using monostable multi vibrator .

    Can this work or i will have to do other type like CCP or Comparator.

    Please guide me for this.

    Thank You.



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    Re: Photo diode with basic circuit

    It's a question what are the boundaries of the pic's detection ranges, which will cause the pic to recognize 2.45 V as a high?
    Or as a low?
    Or indeterminate?

    Is this on a spec sheet? Did you verify it by your own experiments?

    In addition you must make the pulse last long enough so it can be detected at the moment the pic is checking the input pin.

    Is your program executing a waiting loop at that moment? Constantly checking the input pin? That is the straightforward way to catch a quick pulse.

    If this is impossible then perhaps the pulse needs to last longer than a microsecond.

    As you state, a pulse stretcher can do this. A one-shot will do this.

    A frequent method is to use a 555 IC in one-shot mode.



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    Re: Photo diode with basic circuit

    hi,

    Thanks for reply me i write a program for external interrupt(INT0) for pic controller .

    I am using PIC18F46J11,And in that i am using INT0 for the interrupt detection for the high edge.

    My code is fully built & simulate also but when it implemented on hardware practically could not work...

    I also post new thread for interrupt based detection code....

    Yes, you are right i don't know about how pic can be judge that 2.3V or other value as high and less than this is low level......

    This is the very important one.....
    but in any controller how can we know that the particular voltage is for high level & other is for low level detection ?

    Please give me some guidance regarding this.



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    Re: Photo diode with basic circuit

    Link to a website with a chart showing which voltages are detected as digital high or low:

    Logic Voltage Thresholds for TTL, CMOS, LVCMOS, and GTLP IC families

    With most families of IC's, 2.45 V will be regarded as a high.

    You must also ensure that your signal goes below 0.8 V, to be regarded as a low.

    The obvious way to make sure whether your op amp is producing enough swing...

    is to shine the laser on the photodiode for a slightly longer time.

    One microsecond is a very short time for a train of devices to detect. That is the reason it pays to reduce any slack in activation times, in the sense that you want to hook up the diode so that it's pre-biased to the threshold of responding, and furthermore to construct your op amp circuit so it reponds as quickly as possible.



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