Strange behaviour - Oscillator, PIC and COMMON GROUND

Discussion in 'Embedded Systems and Microcontrollers' started by Neyolight, Mar 5, 2012.

  1. Neyolight

    Thread Starter Member

    Dec 13, 2011
    54
    3
    Hi

    Let me begin by explaining what I have: LC Oscillator , PIC , UART.

    The LC Oscillator oscillates at a frequency (120 KHz in my case) --> This frequency is converted to a digital wave for PIC to read ---> PIC reads the rising edges of the digital wave in a fixed time ( Frequency) ---> This value is sent to my laptop.

    Ok now to the strange part, previously I had no common ground b/w the LC oscillator ( which is on a breadboard right now) and my PIC ( on a PICDEM2 PLUS board). I use to read random values , much lower my current frequency (120Khz).

    Today ( infact just now) I added a common ground b/w the LC oscillator ( on breadboard) and the PIC by connecting the Vss of the PIC to -ve end of the breadboard. The PIC is powered by 9V DC ( AC_DC regulator) and the breadboard is powered by 9V battery (Energizer).

    So with the common ground I see '0' on my UART output and without a common ground I get 1500 -1800 values on my laptop!

    Why is having a common ground giving me 0s ?

    The input I see on PIC hasnt changed after common ground, its still 2.4 V with 120 Khz.....then is UART affected so badly by common ground?

    Any idea as to why that is happening?
    Thanks
     
  2. be80be

    Senior Member

    Jul 5, 2008
    431
    57
    They all need common ground Pic, bread board and UART all need to be tied to the ground

    You say 9 volts your using regulator to bring this down to 5 volts right?

    Only time I have seen this happen it was because of the UART not being grounded to the board with the pic
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,669
    804
    can you post a schematic?
     
  4. Neyolight

    Thread Starter Member

    Dec 13, 2011
    54
    3
    I do have a common ground, Uart is a part of the Microchip board so its om common grounds with the PIC and the circuit
     
  5. Neyolight

    Thread Starter Member

    Dec 13, 2011
    54
    3

    Is there a way to check this?
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    An ohmmeter would do.

    Seeing a schematic (or even a block diagram may even do), and perhaps a picture of your setup may help us understand what you are seeing.
     
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