noise problem with PIC18f4550(DIP 40 pins) and PIC18f2550(DIP 24 pins).

Discussion in 'Embedded Systems and Microcontrollers' started by a_m, Jul 23, 2009.

  1. a_m

    Thread Starter New Member

    Jul 23, 2009
    2
    0
    I have noise problem with PIC18f4550(DIP 40 pins) and PIC18f2550(dip 24 pins).
    In my boards (minimum system) when i move my hand near the PIC micro, clock of micro becomes unstable and when I move my hand far from pic micro, it works good.(I see micro clock in oscope)
    I tested a lot of ways. For example:
    1)Two capacitors with low ESR( such as tantal 100uf) and 1mH inductor in VCC for noise reduction.(Low pass filter)
    2) Disable or enable all of fuse bits such as (clock fail and ...)
    3) Decrease clock speed (12, 8, 4 MHz)
    4) Internal clock (8MHz)
    5) External clock (1 MHz) with signal generator
    6) Very Stable Power supply 5v
    7) Disable interrupts
    8) Disable external reset (MCLR)
    But our PIC minimum system is sensitive to my hand noise.
    I don’t have this problem with PIC32MX440F512H.
    In short term solution I designed a little box and I covered it with AL (conductive element) and connected it to GND then I put my board in box for EMC. It works well and it is independent from environment.
    But in long term I don’t have any solution. Please help me.
     
  2. a_m

    Thread Starter New Member

    Jul 23, 2009
    2
    0
    Thanks for your answers.
    I got answer. I had a bad mistake.
    I disable LVP or pull down PGM pin and it works well...
    thank you
     
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