On 10/19/05, alan smith <micro_eng2@yahoo.com> wrote:
> This is going to be another one of those....really wierd problems.  OK, so
> we have a board design, using a 18F4680, I as the developer have a couple
> while the client has a couple as well.  I develop the code, test it best I
> can, send it off to him where he dumps it down to his target board to look
> for issues, etc.   99% of it works correctly, but the analog seems to be
> really wierd.  On my boards, I am measuring the Vin (thru a divider of
> course) and another analog input from an onboard sensor.  I test...send to
> him, he says....no data, or whats even stranger, the analog data is stuck at
> 7F.  The boards are running off a 3.3V DC/DC module so all is well there.

Are you sure or you didn't ever check with a scope, like somewhere
else from this list was saying ? There is no DC/DC converter which you
may say is well for an analogic measurement.

cheers,
Vasile


> So finally I said....send me YOUR board let me look...sure enough, the
> analog is hosed so I swap out the chip. I cycle once time thru the code, see
> good (semi valid) data and the next time....it goes bad and stays bad.
> Hmmmm.   So I change to another chip...3rd time, half the analog works fine
> meaing the voltage meas!
>  urement
>  is OK but the sensor data is not.  I take the chips that didnt work
> correctly, drop into my board...works just fine.  I can now see why the
> client is so frustrated...nothing I sent him would appear to work right.  So
> I am going to send my board to him...etc...so he can continue testing while
> I try and figure out what the deal is on his.  And yes, I did measure the
> voltage on the pins and its where I would expect it to be for both Vin and
> sensor data on the "bad" board.  I've done all the visual checks on
> components to make sure nothing was in backwards, wrong part, etc.  All the
> normal things one would do when first diving into a problem like this.
>
> So, making a long story short....anyone ever seen where the PIC A/D gets
> "stuck" on a certain value and doesn't want to change?  I'll have to go back
> and look at unused pins, but pretty sure that they are all tied to something
> right now.
>
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