how ti reverse a photoresistor

Discussion in 'General Electronics Chat' started by Juan Arnold Rabino, Sep 17, 2015.

  1. Juan Arnold Rabino

    Thread Starter New Member

    Sep 17, 2015
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    Ive made up a laser security sytem that uses a pnp and npn transistor so that even when the laser is tripped the LED will stay on . Everything is going well except for the LDR. When there is no light the led will stay off. And once there is light it will turn on. How do i reverse it? here is my diagram. Please help.
     
  2. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    527
    Use an inverter.
     
  3. dannyf

    Well-Known Member

    Sep 13, 2015
    1,775
    360
    Use a transistor to reverse the output's phase.
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,518
    1,247
    Your question is missing a LOT of details. Also, there is no LDR or laser in your schematic. What is the function of the switch? Also, what does the circuit do? Does it sound an alarm or some other kind of indicator that the system has been tripped? What is it you are trying to do?

    Ask a better question, get a better answer.

    ak
     
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