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  1. #1
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    how to use a photodiode

    Hi,

    A few days ago, I got my self a an IR led and an IR 'sensor'. The IR led looks just like a normal transparent red LED but it is supposed to radiate IR.

    The sensor on the other hand looks very peculiar and is completely black in color and covered. I am not so sure on how to use this particular component.

    Will the sensor output a HIGH or a LOW when ANY IR light falls over it? Or will it respond to 50% duty cycle 38 KHz carrier wave ? I have done some googling and found most proximity detectors make use of a 38 Khz carrier wave.

    Any pointers ?

    thanks in advance,
    Seemanta

    •   Alt3rd November 2008, 12:38

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    using photodiodes

    The sensor is transparent to IR but opaque to visible light, hence the black colour. Unless you are just using photodiodes, you probably have a matched pair TX/RX.
    The detectors are usually combined detectors and integrated ICs. Dependent on type, they require a 38k input carrier, modulated with the data stream. Output is just the data stream. Most remote control encoders for this job will generate the carrier and data for you. Do a bit of googling for IR decoders, Holtek etc.



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    ir photodiode circuit

    Unless you are just using photodiodes, you probably have a matched pair TX/RX.
    That's the problem! I do not have any matched TX/RX set. Just an IR LED and a photodiode. I shall do a bit more research on the data stream approach, but in the meantime can you provide some pointers on how to use a plain photodiode to detect IR ?

    regards,
    Seemanta



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    using a photodiode

    If your IR sensor has 3 legs then it is an IR receiver IC.
    If it has 2 legs then it might be a photo diode.

    A photo diode can be used in 2 ways:
    1) When fed a reverse voltage through a high value resistor (100k) then it conducts a little when it detects light. It will need an amplifier. The reverse bias reduces its capacitance so it switches quickly.
    2) When it is connected to the inverting input of an opamp that has a negative feedback resistor then it generates a small current like a solar cell which is amplified by the opamp. It switches fairly slowly.



    •   Alt4th November 2008, 02:26

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    how to use photodiode

    I want to contradict the comparison of photodiode circuits.

    Although the photodiode's junction capacitance is considerably higher with zero bias, the active V/I converter circuit will show a higher bandwidth in most cases, utilizing an OP with sufficient GBW (not a lousy 741) and appropriate compensation. Because the latter circuits properties mainly depend on the OP, both are hardly comparable to my opinion.



    •   Alt4th November 2008, 06:54

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    ir receiver photodiode

    Perhaps if you could give an idea of your application, we may be able to offer you better suggestions. Possibly a LDR may be bore suitable if you do not need to send data.



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    ir receiver using photodiode

    Quote Originally Posted by FvM
    I want to contradict the comparison of photodiode circuits.

    Although the photodiode's junction capacitance is considerably higher with zero bias, the active V/I converter circuit will show a higher bandwidth in most cases, utilizing an OP with sufficient GBW (not a lousy 741) and appropriate compensation. Because the latter circuits properties mainly depend on the OP, both are hardly comparable to my opinion.
    All the sites with photodiode theory say what I said about photodiode circuits.
    Usuall both modes of operation use the same opamp as an amplifier.



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    ir photodiode circuits




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    using photodiode

    The first circuit doesn't show photovoltaic mode rather than a nonsense circuit, where the photo current goes no nowhere. The ground connection is missing,

    The shown photoconductive mode, where a biased diode is directly connected to a V/I converter is however different from what you described above:
    1) When fed a reverse voltage through a high value resistor (100k) then it conducts a little when it detects light. It will need an amplifier. The reverse bias reduces its capacitance so it switches quickly.
    The shown circuit is rather a photodiode
    connected to the inverting input of an opamp that has a negative feedback resistor
    but with an additional bias. So , what "All the sites with photodiode theory say" is a bit different from what you explained previously. When connected to an identical V/I converter, the biased diode is actually faster, but surely not with "a high value resistor (100k)" series connected.

    But I think, we have sufficiently illuminated the field of photo-diode circuits.this time.



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    ir photodiode receiver

    The site in the UK had the schematic missing a 0V connection. Another site in the UK had it correct.

    I was wrong when I said a series resistor. I was thinking about the collector resistor of a photo-transistor.



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    ir receiver photodiode circuits

    Quote Originally Posted by Audioguru
    If your IR sensor has 3 legs then it is an IR receiver IC.
    If it has 2 legs then it might be a photo diode.

    A photo diode can be used in 2 ways:
    1) When fed a reverse voltage through a high value resistor (100k) then it conducts a little when it detects light. It will need an amplifier. The reverse bias reduces its capacitance so it switches quickly.
    2) When it is connected to the inverting input of an opamp that has a negative feedback resistor then it generates a small current like a solar cell which is amplified by the opamp. It switches fairly slowly.
    Hi everybody,

    sorry to dig up this thread, but there is circuits using a photodiode output as voltage input for an analog comparator without adding an opamp as converter (fig 2 in the linked file).


    http://www.ee.iitb.ac.in/~spilab/Pub..._drip_rate.pdf

    Page 5/ III. INSTRUMENT DESIGN / paragraph2
    The instrument circuit is shown in Fig.2. The
    sensor assembly uses an infrared LED – photodiode pair
    to sense the passage of drops through the drip chamber.
    Use of infrared sensor reduces the effect of ambient
    light and also the effect of variation in transmittivity of
    different fluids. Normally the light from diode D1 after
    passing through the chamber is incident on the reverse
    biased photodiode D2 resulting in voltage Va. When a
    drop passes through the chamber, the passage of light is
    interrupted, resulting in a voltage drop. Voltage Vb,
    obtained by low-pass filtering Va using R3-C3, serves as
    reference input to the microcontroller’s internal analog
    comparator. Dipping of Va below Vb results in a pulse at
    the comparator output.



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    photodiode reverse voltage connection

    Hai seemanta
    This ready to use IR obstacle detector Module from united 7 technologies can be used in wide range of applications where ever an indication is required when an obstacle is detected as the module gives "Low output" The details is as given below, and the complete module costs just 200/- Rupees, measuring just 1 Inch x 1.5 Inch.

    Infrared Obstacle detector.....................200/-
    This circuit can be put to variety of uses where obstacle detection is required. The circuit emits modulated infrared beam through IR led and receives the reflected light back and trigger a “low” logic when ever an obstacle is detected. The range of detection can be varied up to 4-6 inches for white surface with on-board variable resistor.

    Good luck



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    infrared opaque fluids

    Amplify the current with a transimpedance amplifier just not that if you do not provide lag compensation on the feedback the circuit may oscillate. The photodiode in general will produce a current and a voltage but you want to amplify the current since the current component is linear whereas the voltage is not.



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    Re: How to use IR detecting photodiodes...

    I think i have burnt the IR receiver. I wanted to extend the IR receiver by removing it from the circuit board and installing on the case. I removing it with a normal soldering iron. Then i connected the IR receiver with wires to the circuit board.

    How to search for replacements? the old IR receiver says, "GW" on the back and 8814 on the front. Any pointers on how to get equivalent replacemnets ?



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