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Thread: High LDR resistance problem....

  1. #1

    Default High LDR resistance problem....

    i am making a train model with automatic road barriers. i wish to use LDR and a torch to operate the barrier switch but the current output from the LDR is too less to make a relay work..


    a circuit to increase the sensitivity of the LDR is required plz help??

  2. #2
    Senior Member T-1000 akshay66's Avatar
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    Default LDR PROBLEM!!!!!!!!

    Which size of LDR are u using?How much output you want?Pls tell in detail.
    Redefine it your way!!!!

  3. #3
    Senior Member T-1000 akshay66's Avatar
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    Default

    Are you using a torch or laser for source of light I'de preffer laser they are more accurate.
    Redefine it your way!!!!

  4. #4
    Senior Member T-1000 debu's Avatar
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    Default

    Are you using a torch or laser for source of light I'de preffer laser they are more accurate.
    @akshay66: :!: What did gopalr ask?

    @gopalr: An LDR is a resistance, so you can't use it directly to switch a relay. How you should use it is, use an Op Amp (LM324 or equivalent IC), as a comparator. Use a potentiometer, and compare the output of the LDR against the adjustable output of the pot. Use the output of the comparator to switch an NPN and sink to switch the relay.

    In this way you can adjust the sensitivity of the circuit by adjusting the pot and compensate for any ambient light problems with the LDR.

    Hope this helps,

    Regards,

    Debu

  5. #5

    Default

    i am using a torch, and i want around 12 volts output..


    Debu,

    which NPN transistor should i use i have seen 2 circuits they use BC107-108 but they are not even available in Lajpat Rai Market.

  6. #6
    Senior Member T-1000 debu's Avatar
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    Default

    @gopalr: Use a BC547 or BC548. These are very common, and would cost you Rs. 3 each.

    Regards,

    Debu

  7. #7

    Default

    check out the new topics....
    regards
    sid

  8. #8
    Senior Member Cyborg
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    Default

    http://www.technologystudent.com/images5/ldrmtr1.gif
    use 47K connected to ground ad ldr use 1k resistance to base of transistor (2N3904) diode 1n4007 , 12 V sugar cube will also work u can use 9-12 v supply
    http://www.onlinetps.com/
    Online Component Shoppe
    Microcontrollers and Solar Robotics Stuffs at cheap rates

  9. #9
    Senior Member Cyborg
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    Default

    use 47K connected to ground and ldr use 1k resistance to base of transistor (2N3904) diode 1n4007 , 12 V sugar cube will also work u can use 9-12 v supply
    http://www.onlinetps.com/
    Online Component Shoppe
    Microcontrollers and Solar Robotics Stuffs at cheap rates

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