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Configuration for reset options on the PIC12F683 for Wig-W

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nuckolls.bob(at)aeroelect
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Posted: Sat Apr 28, 2012 9:15 am Post subject: Configuration for reset options on the PIC12F683 for Wig-W

At 01:28 PM 4/27/2012, you wrote:




Bob,



I had a question on which of the reset options should be set up

for the PIC12F683 on the wig-wag project besides the Power

On Reset. Looking at the PIC12F683 document it wasn't obvious

to me which options to enable...



Should the Brown Out Reset and the Power On Timer

functions be enabled for the chip?



    I think I'd go for the usual orderly start

    at power up. This isn't a system that is likely

    to wander off into the weeds . . . or create a

    tense day in the cockpit if it did.



    Your question gives rise to an interesting

    follow on. Suppose the thing simply craps. How

    will the pilot know it?



    On first pass I seems that a pre-flight test

    might be satisfied by turning the system on

    to both mode and watching for certain increase

    in load current for both modes. This pre-supposes

    the airplane is fitted with loads instrumentation

    with enough resolution to detect the new, lower

    current LED fixtures.



    Alternatively, we might add a tell-tale led to

    the installation drawings that comes on with just

    one of lamps. One could see that it flashes in

    wig-wag mode and is steady in landing light mode.



    If I were offering a product like this to the

    TC aircraft world, they would probably ask for

    a FAIL detector and light driver. Can be done

    with a two resistors, small fet and a capacitor.



    There's enough room on the board but we'd have

    to shuffle some pins.



    Good question to address in the PPOC (post proof

    of concept) phase. For now, assume all is right

    with the world after spool-up from cold start and

    revisit this later.

Also, did you want the external reset line (MCLR) to be enabled?



   No, it's pulled up with an external resistor and

   used as an general purpose input only.

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Apr 28, 2012 9:37 am Post subject: Configuration for reset options on the PIC12F683 for Wig-W

Alternatively, we might add a tell-tale led to

    the installation drawings that comes on with just

    one of lamps. One could see that it flashes in

    wig-wag mode and is steady in landing light mode.



    If I were offering a product like this to the

    TC aircraft world, they would probably ask for

    a FAIL detector and light driver. Can be done

    with a two resistors, small fet and a capacitor.



-----------------------



    Expanding that train of thought. GP2(Pin5) is not

    used in the Wig-Wag controller. You could write this

    port HI and LO along with, say GP5(Pin 2). We could

    wire an external LED from P1-10 to ground. The pull

    up would give 1 mA of drive to the LED . . . probably

    enough for useful light output as a tell-tale.



    This argues with the legacy philosophy of never taking

    any connection to silicon directly to the outside world.

    In this case, the LED would be on the end of a shielded

    wire terminated at the controller. This level of protection

    from ingress of EMC uglies is probably sufficient to

    protect the PICChip. I'll pray over that idea some

    more . . .



   Bob . . .

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