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> From:
> To: piclist
> Subject: Fw: Intermittent Problems
> Date: 05 April 1997 22:29
>
>
>
> ----------
> > From: John Waterman <john@neutrino.softnet.co.uk>
> > To: piclist <piclist@mitva.mit.edu>
> > Subject: Intermittent Problems
> > Date: 05 April 1997 19:45
> >
> > I am a newcomer to PICs and have been having problems with my first
> > project. I am using a 16C84 with Port A as all inputs and Port B as all
> > outputs. Initially the PIC was just controlling LEDs, and although it
> > worked fine most of the time, occasionally an output would come on for
no
> > apparent reason. The only interrupt I am using is the RTCC overflow one
> and
> > I take the precaution of saving W and STATUS at the beginning of the
> > interrupt routine and restoring them at the end.
> >
> > I carried on with the project and connected the outputs to solid state
> > relays which in turn control contactors using 110volt a.c. coils.
> Whenever
> > the 110volts was turned on the problem became considerably worse. I
then
> > discovered that by replacing a sequence such as
> >
> > BCF         PORTB,0
> > BSF         PORTB,1
> > with
> > MOVLW       2
> > MOVWF       PORTB
> > the problem decreased dramatically.
> >
> > I have a subroutine which redefines the TRISs and OPTION, and I call
this
> > before virtually all I/O read or writes as recommended in the data
sheet
> > for a noisy environment. I also discovered that by putting a delay of
> > around 50mS at the end of this subroutine the program then became
> virtually
> > trouble free. An occasional problem would occur at just one part of the
> > cycle, but this was 'side-stepped' by changing the sequence of events
and
> > then everything appeared to be fine.
> >
> > I carried on further, and connected the outputs from the contactors to
> > 415volt 3phase
> > motors, and with these motors running under no load conditions
everything
> > still appeared to be fine, although testing at this stage was rather
> > limited. When however the machine was put on load, problems returned.
> > Sometimes it will work fine but at other times it will go wrong in an
> > unpredictable manner. I have put varistors across the 110volt coils but
> > with little or no effect. The PIC is inside a metal box maybe around
10cm
> > from the nearest contactor and all the input cables are screened - what
> > more can I do?
> >
> > Please help or I think I may soon be looking for another job!
> >
> > John Waterman