LDR - Transistor

Discussion in 'General Electronics Chat' started by FroceMaster, Apr 11, 2015.

  1. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Hi.
    Have this Circuit
    When the lights reach LDR1, the resistance drops, and the T8 close, and the RESET on IC3 gets high( no Counts).
    when the dark hits LDR1 the resistance rise and the T8 opens up, and the RESET on IC3 gets low( Count)

    will this be right or have i missed something. ?
    If it is ok, then i could replace R16 with a VR. to adjust the time of darkness.
    The value of R17 = 5k?
    The value of R18 = 10k?
    R16 maybe 20k, LDR is 200k in the dark, 6k in light.
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    I would make R16 100k, so when daylight is present the voltage across the Ldr at 6K, will be approx 0.28V, so Tr1 will be off.
     
  3. FroceMaster

    Thread Starter Member

    Jan 28, 2012
    400
    4
    Ok. But will the RESET of ic3 work. Or do i need some gate or something ?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    yes when the transistor is turned off, as long as the voltage across the Ldr is less than 0.7V, the chip will be reset.
     
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