A CMOS 555 works well, temperature drift may be an issue. The input voltage
has to be kept in the 1/3 to 2/3 Vcc range. You can get very high resolution
on slowly changing signals such as temperature by counting for longer.
Accuracy depends on the linearity of the VCO transfer function, which can be
corrected for if necessary. For higher sampling rates measure the width of
single pulses.
/\/\/\/*=Martin

----- Original Message -----
From: "marco genovesi" <marco.genovesi@LIBERO.IT>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, February 21, 2002 10:36 AM
Subject: [EE]: A cheap A/D interface


> Hi all,
> I have to interface my 16F84 Datalogger ( 4.5V supply) with sensors that
> have a voltage output, but in my board I have only one free pin (RA4), so
> I'm thinking to a voltage-frequency converter. I need 8 bit resolution.
> For a lot of reasons, I would like a really cheap solution, preferably not
> over 2-3$.
> I have seen that a 4046 CMOS has a voltage-controlled oscillator, but I
> haven't never used it: can it be an acceptable solution for my specs or
I'm
> going in a wrong way? Have anyone any suggestion about 4046 VCO use or
other
> low cost alternatives?
> Thanks in advance
>
> Marco
>
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