[sdiy] Analog division

[cheater cheater]

Tim,
a logarithm can only be evaluated at a positive number. If this module
accepts negative numbers then it does not count their logarithm. It
can be said to be a generalized logarithm function.

Cheers,
D.

On Mon, Jul 19, 2010 at 21:25, Tim Daugard <daugard at cox.net> wrote:
> From: "cheater cheater" <cheater00 at gmail.com>
> you can only take logarithms of positive numbers, so it wouldn't work
> without modifications. However you can rectify each signal and extract
> the sign with a comparator, then multiply them with e.g. an AND gate,
> and apply that to the output. Then you should be fine, I think.
>
> This module:
>
> http://members.cox.net/synthfred/h_alg121.htm
>
> provides a signal that is the log of the signal centered on the reference
> voltage at the top of C7. If you look at the description, it takes the log
> of both the positive and the negative going portion of the signal. The
> waveforms from the theory section match the waveforms from the built module.
>
> The math would be:
>
> ref+(log(sig-ref)) -->  if the signal is greater than the ref
>
> OR
>
> ref-(log(ref-sig)) --> if the signal is less than the ref.
>
> I'm not positive I got the math right but, the figures are 100% verfified.
>
> Tim Daugard
> AG4GZ 30.4078N 86.6227W Alt: 12 feet above MSL
> http://members.cox.net/synthfred/h_toctop.htm (Fred's online edition)
>
>
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