Look at Scott Datallo's "Sigma Delta Converter".
Can't get cheaper than that.
RA4 would not be the best pin for that though.

4046 may be marginal on linearity to achieve 8 bits without quite a lot of
work.
Still be cheapish though.

You can do a fair dual slope VCO with an opamp (even a cheap LM324) plus
perhaps 1 transistor
NatSemi do an app note for this in the LM324 data sheet AFAIR.


      Russell McMahon


> 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?

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