I was thinking that you would send BOTH the frequency component AND what was
left of the original signal after removing that component.

The point is to gain intelligence about the signal and therefore transmit
less information while still conveying the entire original.

The big problem is the bandwidth into and out of a PC. If you can use analog
components to compress the amount of data needed, then a smaller, slower A2D
can still be effective. 

---
James.
 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Mark Rages
> Sent: 2005 Feb 07, Mon 09:38
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Poor man's very low frequency oscilloscope.
> Importance: Low
> 
> On Mon, 7 Feb 2005 08:07:30 -0800, James Newtons Massmind 
> <jamesnewton@massmind.org> wrote:
> 
> > E.g. use a frequency to voltage converter to find what 
> frequency the 
> > signal is, and then filter out that AC component. Send only the 
> > frequency and the remaining DC signal to the PC. Now, in 
> the PC, use a 
> > program to reconstruct what the original signal was based 
> on the information.
> 
> That's all you need for a signal that is DC+a single 
> frequency component, although you cannot construct the 
> original signal without also having phase and amplitude information.
> 
> The real problem with this approach is that most signals will 
> have more than one frequency component.
> 
> > How you do that is a good question. I know exactly how it 
> is done in 
> > software, and I could guess at a digital circuit that would 
> do it, but 
> > in the analog world I'm worse than clueless: I come up with really 
> > strange ideas! <GRIN>
> 
> You need to understand Fourier analysis to understand this 
> kind of problem.  Not *how* to do the Fourier transform, just 
> the concepts involved.
> 
> > Perhaps something like an audio equalizer? Is it not true that a 
> > filter both removes part of the signal but can also be used 
> to measure 
> > how much of the signal is being removed and by knowing the 
> electrical 
> > characteristics of the filter that signal can be reconstructed and 
> > re-injected into the remaining signal at a later date?
> >
> > There was a system used years ago called "audio companding" which 
> > "compressed" the high frequency signal for tape recorders. It was 
> > combined with another circuit for play back that 
> re-expanded the signal on playback.
> > 
> > Some sort of calibration would probably be needed to set up the 
> > software as an accurate negative model of the analog component...
> > 
> > A quick Google for ["analog data compression" circuit] came up with:
> > http://www.freepatentsonline.com/image-4441183-1.html which looks 
> > really interesting, although it is more digital than analog.
> 
> Actually that looks like something you might see in a PIC 
> datasheet: a way for one pin to measure digital or analog 
> voltages, switchablew by software.
> 
> If this kind of thing iterests you, you might want to look at 
> "pre-digital" computer technology, such as the Philbrick 
> Applications Manual for Computer Amplifiers.
> 
> Regards,
> Mark
> markrages@gmail
> 
> --
> "We act as though comfort and luxury were the chief 
> requirements of life, when all that we need to make us happy 
> is something to be enthusiastic about."
> 
> - Einstein
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