Em 8/6/2010 09:08, Olin Lathrop escreveu:
> Yigit Turgut wrote:
>   =

>> You say the values are correct and then you say the circuit is really
>> bad, which one?
>>     =

> Both, since they are not mutually exclusive of course.  I said the values
> you reported from the A/D seemed correct given what you were driving it
> with.  That doesn't mean the way you were driving it was a good idea, and=
 in
> fact it wasn't.
>
>   =

>> It is basicly "
>>
>>     =

> http://www.best-microcontroller-projects.com/support-files/lcd-volt-meter=
.pdf"
>   =

>> this circuit, I just ported it to usart.
>>     =

> First, just because someone wrote up a circuit doesn't make it a good one.
> Any idiot can put up a web page.  However in this case the circuit looks
> reasonable enough at first glance.  Second, most of that circuit is not
> relevant to the discussion, which is about how to drive the PIC A/D input.
> That circuit merely shows the A/D input coming from elsewhere.  Note that=
 it
> specifically states "Input 0-5V", which is correct.  Your circuit does not
> adhere to that, which is the "really bad" part I was referring to above.
>
> The reason I said "really bad" instead of merely "bad" is that not only
> can't the A/D measure values below ground, but strange and possibly damag=
ing
> things can happen to the PIC when you cause enough current to be conducted
> thru a pin protection diode, especially if that happens during powerup.
>   =



The reset circuitry in the PDF seems not correct.
I couldn't find decoupling caps also.

And where is the most important circuit, the current sense itself?

Isaac
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