> Does anyone have a block diagram of the ( voltage ? )
> reading-to-audio-tone electronics ?

Taking that almost unbelievable question at face value.

1. Draw rectangle

Label rectangle "VCO"
Add input - label Vin.
Add output - label Fout
QED.

or

2. Use CD4046 block diagram.
Essentially as above with a few support components thrown in to set
frequency per Volt etc.

http://focus.ti.com/lit/ds/symlink/cd4046b.pdf

3. For extra points add a simple differential amplifier which amplifies the
small voltage beteen its probes to a level that best suits the 4046.


   Russell
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