I don't know what you think about this solution for an acurate reference voltage- but many old measuring devices which use wheatstone bridges use a battery ( mercury cell 1.4V.. I can't remember exactly) They last for years because you're not really drawing much current from it -and their voltage remains extremely stable over time. Probably not the ideal solution- but one of the quickest and cheapest. -- Jon Baker ----- Original Message ----- From: "Vasile Surducan" To: Sent: Thursday, January 10, 2002 11:40 AM Subject: Re: [PIC]: Low cost A to D reference > 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 > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.