The idea is the following:
We want a digital logarithmic potentiometer but we don't have one. Let us build one out of two linear potentiometers! (We put them in series.)
The GNU Octave script "calc_lookup.m" calculates a set of wiper settings combinations for both potentiometers which make the combined circuit act like a logarithmic potentiometer.
Linux users: Install GNU Octave with your usual package manager, e.g. sudo apt-get install octave
Open a terminal, "cd" to the folder containing calc_lookup.m and call the script by typing "octave calc_lookup.m" It generates several plots and a look-up table in csv format.
Windows users: You can use Cygwin, which is a Linux like software distribution. (https://cygwin.com/install.html) In the install wizard search and mark the package "octave" for installation. Then open the cygwin terminal, "cd" to the folder containing calc_lookup.m and call the script by typing: "octave calc_lookup.m" It generates several plots and a look-up table in csv format.
Go to http://acidbourbon.wordpress.com/2016/10/01/brute_force_logpots to read the full details about this and other projects.
2016 by Michael Wiebusch