PIC false digi I triggers

Discussion in 'General Electronics Chat' started by gdallas, Mar 26, 2014.

  1. gdallas

    Thread Starter Member

    Apr 25, 2012
    74
    0
    I’m experiencing false triggers of digi switch inputs (on occasion) and not sure what’s causing this. I’m using a pic 18f, with interrupt driven switches on PortB. I have external 100k weak pull-ups (needed due to power constraints) and note that the voltage is held high at around 3.02V which is a fair ceiling above the high input min value of 1.7V.
    Observations:
    When touching negative terminal (only) of DVM to board ground, it triggers a false activation. This is quite repeatable. On occasion, when momentarily pulling another switch low , I see it affect the logic on another pin, but only on occasion. I’ve put in 0.1uF caps on the DI pins, but this hasn’t really helped. Any ideas what’s causing this? Anything to do with interrupts and or switch bounce?


    VDD
    3.6
    V
    Input Low Voltage (Max)
    0.54
    V
    Input High Voltage (Min)
    1.7
    V
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    U need to debounce the switches. You can use delay in the software routine to debounce all the switches

    Plus decouple the PIC power pins with 0.1uF caps and a 10uF cap. Place them close to the PIC power pins
     
  3. gdallas

    Thread Starter Member

    Apr 25, 2012
    74
    0
    ye i think thats the issue, I have the software guy on teh case. thanks for the confirmaton.
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,393
    1,606
    There is a reason they are called "weak" pullups.

    Care to guess why?
     
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