Tie +Vref to a constant voltage source or a zener diode


----- Original Message -----
From: "Mike Singer" <mike@POLUOSTROV.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, June 27, 2002 3:04 PM
Subject: Re: [PIC]: Monitoring a voltage with a 16F877? the same voltage
source??


>    Brandon, I envy slightly you posted this message, not me.
> I was always wondering, what is going on inside the computer
> case with current flows, cause I'm forced to deal with cheap
> uncertified Chinee's cases.
>    One can literally hear this flows connecting Motherboard
> Sound Input to spare black ground wire of power supply.
>    I'm convinced, special advanced approach should be
> taken, when investigating current & voltage distribution inside
> the case. I'm not EE professional, nevertheless I suppose,
> you should get a sort of MSP430FXXX 16-Bit Ultra-Low-Power
> Microcontroller, from batteries powered.
>    It should be well shielded. Case ground should not be
> connected to microcontroller null. Microcontroller scheme
> should be galvanicaly decoupled from output, as well as from
> anything, but input.
>    Differential input - two AD inputs with an advanced automatic
> gain control capable of adjusting full scale to approx 0.1(?)v - 30v.
>    And so on...
>
>    Good luck.
>    Mike.
> ----------------------
>
> Brandon Stewart wrote:
> > I am building a project that fits into an empty computer bay and is
> powered
> > from the computer's power supply. This is done off of a 12 volt line and
> > through a 7805 -> which provides the 5V for the PIC to run on. Now, I
plan
> > to set up voltage dividers between the computer's 5 volt line and
ground,
> > and the 12 volt line and ground. This way I can use the A/D inputs of
the
> > PIC to monitor the computer's power supply voltage. This is done by
> > choosing resistor values that provide monitoring voltages at 2.5 volts
for
> > each of the two lines being monitored. This is done to allow for the
> > greatest fluctuation in the power supply voltage, whereby I can still
> > monitor it without 'clipping'.
> >
> > ==> My question is, should I worry about sensing a voltage that is
> > providing the power to my PIC to start with? Remember, I am monitoring a
5
> > & a 12 volt line, and this 12 volt line is the same one that powers my
PIC
> > through a 7805.
>
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