Re: pic a/d problems
From: timmmmayyy! (timmmmayyy_at_nospamplease.com)
Date: 10/23/04
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Date: Sun, 24 Oct 2004 00:19:13 +0100
Reference is the vdd and vss.
It may be the circuit boards, i will put an ic holder on one pcb, and try
different chips within the same circuit.
impedance is 1k
aquasision time is 1ms.
thanks
"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:25hkn0pg3sik7k7r9h3m5ggukcg3va1j11@4ax.com...
> On Sat, 23 Oct 2004 11:13:50 +0100, the renowned "timmmmayyy!"
> <timmmmayyy@nospamplease.com> wrote:
>
> >Has anyone else found this problem?
> >
> >I have many pic18f452 chips and use the a/d converters. I have found that
> >there is a large variation in what x volts will give, varing between chip
to
> >chip.
> >
> >1.55 volts on one chip gave 79 (8 bit result) 83 on others.
> >
> >It is quite strange this and quite anoying.
> >
> >Cheers
> >Timmay!
>
> Not at all, the ADCs meet all specifications when properly applied,
> IME.
>
> Perhaps your acquisition timing is off or your source impedance is too
> high, as Frank suggests (2.5K maximum). Under some (improper)
> conditions you can get voltage from a previously read input affecting
> the current reading. What about the reference voltage?
>
>
> Best regards,
> Spehro Pefhany
> --
> "it's the network..." "The Journey is the reward"
> speff@interlog.com Info for manufacturers:
http://www.trexon.com
> Embedded software/hardware/analog Info for designers:
http://www.speff.com
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