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I'm a total newbie at this, but I have a photoresistor set up so that it controls the shorting on an audio circuit. When light is on, it shorts and cuts the sound. When it is dark, it closes and allows the circuit to run normally. How can I reverse this so that light will make the sensor close the short, thus allowing sound to run through?

More simply, I just want the photoresistor to open with darkness, and cause more resistance with increasing light. Sorry for being so layman about it, but like I said, I'm very new at this. Thanks for any help.

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    \$\begingroup\$ Can you add a schematic? Click edit and type CTRL-M. \$\endgroup\$
    – Phil Frost
    Feb 26, 2014 at 21:13
  • \$\begingroup\$ How is the photo-resistor connected? Is it in a voltage divider or just from the signal to ground? \$\endgroup\$
    – alexan_e
    Feb 26, 2014 at 21:13
  • \$\begingroup\$ Voltage divider \$\endgroup\$ Feb 26, 2014 at 21:17
  • \$\begingroup\$ Then all you need to do is place the resistor in the opposite side of the divider, in that case instead of lowering the resistance to ground it will lower the resistance to the signal. A schematic of your configuration will be useful I think. \$\endgroup\$
    – alexan_e
    Feb 26, 2014 at 21:19
  • \$\begingroup\$ @alexan_e Can you answer the question with a very simple circuit simulation? \$\endgroup\$ Feb 26, 2014 at 21:22

1 Answer 1

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Suppose that you have a divider like the one below and the DC source is the AC signal (using DC helps with the simulator)

schematic

simulate this circuit – Schematic created using CircuitLab

If the photo-resistor is in place of R1 then the output behaves like shown below and the output voltage increases as the resistance lowers (more light) enter image description here

if the photo-resistor is in place of R2 then the output behaves like shown below and the output decreases when the resistance lowers (more light)

enter image description here

In both graphs the vertical axis is the output voltage and the horizontal axis is the resistance value (starting from left side and increasing to the right)

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