This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.


A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it “sees”.


Photoresistors are very inexpensive light detectors, and you’ll find them in cameras, street lights, clock radios, robotics, and more. We’re going to play with one and find out how to detect light using a simple series circuit.


Materials:


  • AA battery case with batteries
  • one CdS cell
  • three alligator wires
  • LED (any color and type)
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Comments

10 Responses to “Electric Eye Sensor”

  1. Aurora Lipper says:

    Please see the explanation of CdS cells at the top of this experiment. A link to purchase a CdS cell is available on the Unit 10 material list.

  2. dowellbethea says:

    What is a CdS cell?

  3. It doesn’t matter which direction you place the LDR (because LDRs don’t have polarity), but it does need to be in series (in a straight line) with the LED.

  4. If your circuit isn’t working, please take a clear, in-focus picture and email it to [email protected]. We’ll try to help you figure out what’s wrong.

  5. ericksonnationmom says:

    do you have to put LDRs in the circuit a specific way in order for it to work???

  6. ericksonnationmom says:

    ok , because it didnt work as a cds and it looks alike

  7. A Light Dependent Resistor (LDR) is a two lead passive electronic part that, like a regular resistor, opposes the flow of current. (passive means it does not take up voltage in order to work. These parts are usually made out of cadmium sulfide (CdS) and change their resistance depending on the amount of light hitting that material. The maximum resistance occurs in the dark and the resistance lowers towards a minimum amount more light hits the sensor. This makes them excellent light sensors. One use is in street lights so they know to turn on when it gets dark outside.

  8. ericksonnationmom says:

    What is a Light Dependent Resistor?
    And what does it do?

  10. can you reverse this to make the LED go on when the lights are off?