[Noisebridge-discuss] seeking circuit idea: frequency to voltage

[Michael Shiloh]

a student wants to build a bar graph type display that will show 
frequency, not voltage. the frequency is in the audio range.

i know there are chips to do this, but i'd like to find a circuit using 
more basic and common components, like a 555, 741, 2n2222, etc.

precision and linearity is not an issue. it's merely a visual element.

any ideas?