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Sharing same LCD between two microcontroller boards.

Discussion in '8051/8951' started by savvej, Mar 16, 2011.

  1. savvej

    savvej Member

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    thanks for pointing out .I need to put pull down resistors from resistor to ground..
     
  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    What value of pull down resistor do have in mind.??
     
  3. savvej

    savvej Member

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    So now the diode design should work right??
     
  4. dave

    Dave New Member

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  5. savvej

    savvej Member

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    10k ..but any higher value will be ok..right??
     
  6. savvej

    savvej Member

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    resistance value should be much greater than input impedance of LCD pin,right?
     
  7. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi,
    The input resistance of the LCD logic is VERY high.
    Its important that you consider the response time of the diode/resistor combination in order to keep the low going 'edges' of the signals going to the LCD within the required specification.

    As the LCD pin low going signal is not an active pull down [ ie: direct connection to a PIC pin], it important that the passive pull down resistor is low enough to get a fast edge.
    I would consider a pull down resistor of 4K7.
     
  8. savvej

    savvej Member

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    Adding diodes and 4k7 resistor did'nt work.
    :(
    But why so?(Currently have solved problem by adding some dpdt switch to connect LCD to required board while operating.)
     
    Last edited: Mar 23, 2011
  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Where did you add the resistors to the circuit,, post a quick sketch
     

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