> Ok Russel,  I like opamp solution. I have found in LM358
> AppNote a VCO example with few low cost components.
> The only problem is a bigger current consumption than 4046
> VCO, if I'm not wrong (my logger must operate for 4-6 months
> with 3 AA cells), so I will try to build and compare the two types of
> circuits.
> Many thanks for support

If you change the F84 for an F628 you can get 3 more i/o lines.
The two OSC pins and Mclr. The advantages are

F628 is cheaper than the F84, and is same pin-out

You can use those 3 lines + the one you have spare now to
operate a serial ADC like the TLC549. Use one for its Vcc,
one for CS, one for Clock and one for Data. The TLC549 is
a cheap, fast and accurate 8 pin 8 bit ADC

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