How do I calculate frequency from an x position on a bode diagram?

Hi,

I'm using the code below to draw a bode diagram manually (drawing code omitted).

It's working reasonably well. In this scenario I have 3 'decades' divided by 10 logarithmic spacings for the x-axis (frequency). I am using the code to calculate the x position for where to draw the bode diagram vertical lines (gridx). In this scenario the grid canvas size is 320 pixels (gridWidth).

However, I'm not sure how I can get a corresponding frequency value from an arbitrary x-position pixel value? So for example, if I clicked somewhere on the canvas, at say, x position 109, what would be the corresponding frequency there?

Any ideas?

Thanks in advance,

Drew

gridWidth = 320;

numDecades = 3;

range = gridWidth / numDecades;

for decade = 0:numDecades-1,

      for index = 1:10,

          gridx = (log(index) * range / log(10.0)) + 0.5 + (decade * range);

          frequency = index * 10 * (10.0^decade);

          fprintf('Decade: %d, index: %d, x: %f, frequency: %f \n', decade, index, gridx, frequency);
      end

      fprintf('\n');
  end

Answer 1

[Youssef Khmou]

Drew, Your code does not return vectors to evaluate the gridx as function of frequency, try this version :

gridWidth = 320;
numDecades = 3;
range = gridWidth / numDecades;
ctr=1;
for decade = 0:numDecades-1,
    for index = 1:10,
        gridx(ctr,index) = (log(index) * range / log(10.0)) + 0.5 + (decade * range);
        frequency(ctr,index) = index * 10 * (10.0^decade);
        fprintf('Decade: %d, index: %d, x: %f, frequency: %f \n', decade, index, gridx, frequency);
    end
    ctr=ctr+1;
    fprintf('\n');
end
figure, plot(frequency, gridx)
xlabel(' Frequency Hz')
grid;

Using canvas, you get the corresponding frequency .