Photo Resistor question

Discussion in 'General Electronics Chat' started by AlexK, Nov 20, 2007.

  1. AlexK

    Thread Starter Active Member

    May 23, 2007
    34
    0
    Hi,

    My question is this: can I connect a photo resistor in place of a resistor
    and expect the circuit to act the same (for a constant amount of light)?

    For example, in the following circuit:
    http://www.radio-electronics.com/info/circuits/opamp_inverting/op-amp_basic_inv.gif

    If I connect my photo resistor in place of R2 will the gain be equal to -Rp/R1?
    (Where Rp is the resistence of the photo resistor for some constant amount of light)

    Thanks.
     
  2. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    a resistance is a resistance.
    What you are proposing is commonly used as the variable gain element in an audio compression/limiting/ or AGC circuit, with the LDR optically connected to a LED or light source whose brightness is determined by the audio level. ... ie. sound gets louder, light gets brighter, LDR resistance decreases, gain decreases pulling the audio level back again.
     
  3. Voltboy

    Active Member

    Jan 10, 2007
    197
    0
    why not using a simple resistor.. less problems
     
  4. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    A photo resistor is not very accurate and has memory. You should expect the gain to be unstable.
     
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