A Little help required!

Discussion in 'General Electronics Chat' started by curriejohn, Apr 19, 2015.

  1. curriejohn

    Thread Starter New Member

    Feb 17, 2015
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    Could anyone help me with a brief explanation on how the attached sensor switch circuit works.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Sure we'll help once we see the circuit.
     
  3. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    And where is the attached sensor?

    Bertus
     
  4. curriejohn

    Thread Starter New Member

    Feb 17, 2015
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    Sorry here it is
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    That is not the complete schematic, it looks there should be something next to R1.

    Bertus
     
  6. curriejohn

    Thread Starter New Member

    Feb 17, 2015
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    sorry Bertus R1 is a LDR
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That circuit will give you a slow gradual turn on of the LED as light changes.
    Max.
     
  8. curriejohn

    Thread Starter New Member

    Feb 17, 2015
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    updated attachement of circuit IMG_2657.JPG
     
  9. wayneh

    Expert

    Sep 9, 2010
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    The circuit works on the relative resistance of the LDR versus R3, which form a voltage divider. This impacts the voltage on the base of the transistor, via R2. When that voltage exceeds ~0.6V, the transistor starts to conduct and the LED lights up. R4 limits the current to prevent damage to the LED.

    The circuit has some problems but probably works.
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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