How long can the cable for an LDR be.

Discussion in 'General Electronics Chat' started by RodneyB, Apr 10, 2014.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Greetings one and all!

    I am trying to find what distance you can run an LDR away from the circuit.

    I have a 12 Volt day night switch using a 741. I want to mount the control unit right next to the battery and the LDR outside about 5 meters away from the control unit.

    Is this possible?
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi Rodney,
    If you use a twisted pair or screened pair of wire to the LDR, 5mtrs is not a problem.
    I would add a 10nF or 100nF across the local end of the wire pair,[the 741 end] to reduce air borne interference.
    E
     
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  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Would I need to solder the screen to the negative or to an earth spike
     
  4. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    That would be good.
     
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  5. ericgibbs

    Senior Member

    Jan 29, 2010
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    380
    If you use a screened pair, connect the screen to the 0V/Common of your project supply.
     
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  6. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Unless the LDR part of the divider is ground referenced, the OP might have to use screened twin.
     
  7. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380

    hi,
    If one end of the LDR is at 0V, surely if he followed my suggestion, all that would happen is that one inner conductor and the screen would be connected together to 0V at the 741 end.?
    E
     
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