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Unstable PIC output - Pins sensitive on touch

Discussion in 'Electronic Basics' started by quiksilv, Oct 18, 2004.

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  1. quiksilv

    quiksilv Guest


    I have a simple LED flasher programmed on a PIC16F877A, but the output
    of the pin (RC4) is always high unless I say put my finger on any one of
    the other pins, then the LED flashes as expected.

    I presume this is capacitance related but what is happening and how can
    I rectify it ?

    The circuit is extremely simple, two 15pF caps on a 4Mhz crystal, an LED
    and 1k resistor on an output pin RC4.

    Thanks !
  2. quiksilv

    quiksilv Guest

    Nevermind, /MCLR had no pullup resistor... durr :)
  3. quiksilv

    quiksilv Guest

    Well it seems now its working but whenever i wave my fingers/hand close
    to the micro (touch some pins or even touch the DIP casing) it still
    goes wierd and keeps the LED on ! If I do this enough the PIC seems to
    stop completely and only re-programming it will fix it.

    This doesnt happen when I ground or vdd myself... what on earth is going
    on ?
  4. quiksilv

    quiksilv Guest

    Ok I solved the problem by disable low voltage programming in the
    config... seems to play havoc with the thing !
  5. Guest

    Is the earth-return connected?
  6. Dingo

    Dingo Guest

    Have you made all the unused pins outputs or tied them high?
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