Usual simple diodes can't be used as reference voltage because:
- drop-out voltage depends by diode flowing current
- there is an important temperature variation of about -2...-2.5 mv/C
But if a 1.25V Maxim reference don't satisfy you because of the price, and
you take care about minimum batteries voltage and choose a good current
it might work. You know better how stable must be your reference.

regards, Vasile

On Thu, 10 Jan 2002, Nigel Duckworth wrote:

> Hi All,
>
> I have to measure my PIC16C711's own battery supply (2 x AA cells) so need to
> generate a reference for the A to D, cost is everything on this one.
>
> I'm tempted to use two diodes in series to ground fed via a resistor from a
> port pin so I can enable the reference only when needed, this should produce a
> nominal 1.4V reference.
> The input volts to the A to D will be divided down from the same port pin so no
> current is consumed while the PIC is sleeping.
>
> The project will operated at room temperature so thermal drift should not be an
> issue.
>
> Has anyone come unstuck doing this in the past?
>
> Thanks in advance.
>
> Nigel
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
>

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body