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  1. #1
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    ldr sensor

    i want to ask about ldr sensor .how they work and how we can use them in simple circuit.

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    ldr sensor circuit

    An LDR is a Light Dependent Resistor i.e its resistance varies with the amount of light falling on it. Resistance becomes lower as the light falling on the LDR increases. A simple circuit would be a voltage divider circuit with an LED connected in parallel with the LDR. When the amount of light decreases the resistance of the LDR increases causing the bulb to light up.



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    ldr circuit

    as above asid that is the most appropirate answer of your question although you can alos check the out put of the light dependent resistor using a simply ohm meter at the out put of the ldr it varies with the source of light.



    •   Alt26th November 2005, 07:16

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    light dependent resistor

    hey i'm using a LDR in a colorimeter. as said earlier.. the resistance varies. here i need to interface it to a muC so.. how do i convert the ohm to voltage?? if i get it in terms of voltage then i can use a v to f .

    if i measure the voltage across the LDR, its varing in the close proximity.
    wht to do????



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    ldr color filter

    why are you using ldr?
    anyway
    you can use filters red filter will detect red....(physcs)
    so the voltage will differ from color to color.
    after simple tests you will be able to know the range of voltages corresponding each color. if thi works out then you do not need a v to f

    but can you give details of your application so that I can help you more or give suggestions?



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    ldr senser

    You can't directly read the LDR into a micro, you have to create a voltage proportional to the LDR resistance then measure that voltage.

    Hint: Potential divider.

    Brian.



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    ldr circuits

    @pakitos
    i'm using the LDR coz its more faster than a phototransistor and it changes in resistance according to the color and irradiance.
    if not LDR.. wht is tht u suggest??

    Added after 4 minutes:

    @betwixt
    hey.. i did use it as a voltage divider. wen i measure the resistance according to the variation in the color/irradiance the variation is noticeable.
    but wen i measure the voltage.. the corresponding voltage, the variation is in the close proximity.
    this ll not help me beacuse i need the system to be accurate. and a very smal change in the color shld represent the corresponding value



    •   Alt4th August 2009, 18:45

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    light dependent resistor circuits

    A similar system is used for measuring chlorine concentration in water supplies, perhaps it could be adapted for your needs.

    It uses two LDRs, one to measure the ambient light and one to measure light passing through liquid. It has the advantage that only the difference is used rather than an absolute level. Although small, the difference is easy to amplify to give better measurement resolution.

    If that isn't a practical alternative, the LDR is still fairly easy to use in a potential divider. Connect it in a bridge configuration and measure it against a fixed value. That can be used to remove residual reading the you can amplify whats left to a larger voltage.

    Incidentally, phototransistors operate MUCH faster than LDRs.

    Brian.



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    light dependent resistor circuit

    Quote Originally Posted by ranjini2311
    @pakitos
    i'm using the LDR coz its more faster than a phototransistor and it changes in resistance according to the color and irradiance.
    if not LDR.. wht is tht u suggest??

    Added after 4 minutes:

    @betwixt
    hey.. i did use it as a voltage divider. wen i measure the resistance according to the variation in the color/irradiance the variation is noticeable.
    but wen i measure the voltage.. the corresponding voltage, the variation is in the close proximity.
    this ll not help me beacuse i need the system to be accurate. and a very smal change in the color shld represent the corresponding value
    Before using different LDR's you always need to measure the resistance in dark and the resistance in light of all the LDR's and it shud be nearly the same. Or else using different LDR's with different values will do nothing more than a headache. Good luck.


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    ldr led circuit

    when im using a phototransistor.. i connect the supply of +5 to the collector, where do i place the base terminal?? is it gnd with emitter??


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  11. #11
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    l d r senser

    For maximum sensitivity, the base terminal should be unconnected. Shorting it to emitter would reduce the sensitivity by a factor of B (several 100).



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    practical on light dependent resistor

    well it seems that my post was removed dont know why?
    what i suggest use a photransistor as sensor ( base not bonnected) and use a bright led as a source of light incident on the body the reflection will be measured by the phototransistor.
    the level of voltage will differ from color to color



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    ldr orcad

    hey how do i use a ldr in orcad pspice? i'm not finding the ldr component in any of the libraries



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    ldr senzor

    you are connecting it practically or just on pspice?



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    measuring light level with ldr circuits

    i wanna do it practically. so i'm trying to simulate in pspice.



  16. #16
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    what is a ldr sensor

    I advise you to start connecting
    http://home.cogeco.ca/~rpaisley4/8PhotoInverting.html
    do some tests to find the voltages used at the comparator


    there is the ldr and the photodiode circuits enjoy



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