At 09:21 PM 1/12/02 -0500, Sean H. Breheny wrote:
>Hi,
>
>Regular PIC inputs are standard CMOS inputs and the threshold DOES change
>linearly with supply voltage. The threshold is close to 1/2 Vdd, so if your
>Vdd falls by 1 volt, the threshold will fall by 1/2 volt, so it won't work
>to use it as a reference. I'm not sure about the Schmitt Trigger inputs,
>but I'd suspect that their threshold is highly Vdd dependent, too.

Well, according to one graph, VinH typically varies from about 0.9Vdc
@Vdd=2.5V through about 1.4Vdc @Vdd=5.5Vdc (DS30561B Pg 112).  Thats for a
non-schmitt trigger input.

Because the change in VinH varies less than the change in Vdd, there should
be enough accuracy available to at least give an indication of battery
voltage.  And if he *IS* using a boost convertor to give a regulated Vdd,
there is no problem at all.

dwayne





Dwayne Reid   <dwayner@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 17 years of Engineering Innovation (1984 - 2001)

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Do NOT send unsolicited commercial email to this email address.
This message neither grants consent to receive unsolicited
commercial email nor is intended to solicit commercial email.

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics