Light Sensor

Discussion in 'The Projects Forum' started by Electrodeman, Jan 19, 2012.

  1. Electrodeman

    Thread Starter New Member

    Jan 19, 2012
    I am building a project that indicates moisture in the soil and when it detects the low resistance in the dry soil turns on an LED. (I already have a circuit for this.)

    I was wondering if anyone had any good ideas how I could use a simple sensor to pick up that light off the LED to signal a pump to activate until the light turns off, in which case the pump turns off.

    Anything would be helpful, I am not quite sure how to really go about it, or what components I would need, but it doesn't sound too hard to accomplish. (Examples are always nice.)

  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    Sure. Use a Light Dependent Resistor (LDR) sometimes called a photocell and often using Cadmium Sulfide. When the LED comes on, the resistance drops dramatically in the LDR, which can be used with an op-amp to bias a transistor which can operate a relay.
    Last edited: Jan 20, 2012
  3. Adjuster

    Late Member

    Dec 26, 2010
    Why do you want to work your pump switching circuit from the light coming from the LED, rather than taking an electrical signal from the circuit?