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Light sensor help

  1. Feb 20, 2007 #1
    I am producing a light sensing subsystem for my "Cookie Jar Alarm" project, which is where basically a product, where if the lid is opened, and the inside of the jar is exposed to light, an alarm goes off. This project is to be made on a breadboard/prototype board. One of these


    This is a circuit I found in my notes,


    however, the range of the LDR's resistances they were using was 0.1Kohms(light) to 100Kohms(darkness), and upon testing an LDR myself, it was 1Mohm when completely immersed in darkness. How do I solve this? Does the above circuit still check out, even when the LDR resistance goes above 100Kohm.

    Remember, I need Vout to be 0V when its in the dark and 12V (or close to 12V) when exposed to light.

    Any other way/circuits I can use to solve this so that I get 0V when its dark, and 12V(or close to) when its exposed to light?

    Last edited by a moderator: Apr 22, 2017
  2. jcsd
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