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

[Michael Shiloh]

555 oscillator with frequency in the audio range. i forget the precise 
values but can find out.

frequency is being varied by a potentiometer. student wants an LED bar 
graph to inducate the frequency (very roughly).

one workaround would be to use a dual potentiometer and use the second 
pot to directly control the bar graph display. i might recommend this to 
him after all.

jim wrote:
>    i love this discussion. best i can tell, the 
> problem definition should be improved: what is 
> the nature of the signal you want to measure, 
> what of that signal do you want to measure, and 
> what's the time constraint of the measurement? 
>    for example, if the signal is voice, we can 
> figure there's a fundamental frequency, there 
> are harmonics, and there's noise. a bar graph 
> indicator that is allowed to be imprecise with 
> a simple, hobbyist-level circuit, can probably 
> only usefully measure something in the domain 
> of power (area under the curve, an integration 
> type of measurement). seems to me at best it 
> might successfully reflect the fundamental 
> frequency of the voice, and that could be dicey 
> in the case of a rapidly changing inflection 
> (some one speaking excitedly), tho' it seems 
> like one might be able to make it useful for 
> singing, where the fundamental is consistent 
> for many, many milliseconds. 
>    hoping for more from the experts, 
> jim 
> 
> 
> 
> 
> On Fri, 2009-12-11 at 10:32 -0800, Christoph Maier wrote:
>> On Thu, 2009-12-10 at 20:55 -0800, Michael Shiloh wrote:
>>> 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?
>> Is independence from the _shape_ of the input signal an issue 
>> (i.e., that a sinewave [=flute] should give the same effect 
>> as a rectangle [=highly overdriven <whatever>])?
>>
>> What do you want to have shown if you feed in a _mix_ of frequencies,
>> i.e., a chord??
>>
>> Jonathan's comments are the correct answer of someone highly Skilled In
>> The Art, 
>> under the implicit assumptions 
>> that you actually want to measure frequency with as little
>> cross-sensitivity as possible, 
>> and that you want to measure the amplitude of each frequency
>> separately. 
>>
>> The other suggestions so far trade off simplicity against
>> cross-sensitivity. 
>>
>> Christoph
>>
>>
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> 
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