The LM3900N I suggested in a previous thread is an amazing device. It is a
current mirror opamp and will function very well with a single +5 volt supply.
I've used them as comparators, general purpose opamps, timers, sinewave
oscillators, filters, voltage regulators, PLL's and mixers. They will easily
source enough current to light an led or drive a small speaker. It is a quad
opamp low current device in a 14 pin dip (also SO) and costs about $.59 ea. and
available almost anywhere.

Level shifting has no effect over the entire bandwidth of the device. It can
operate with a negative supply but is not required.
Rick

Gregory D Wagner wrote:

> Two op amps or two comparators. What you're looking for is called a window
> comparator. The hardest part will be level shifting the signal into the 0
> to 5V range without actually affecting the signal over the whole frequency
> range. You may have to look into generating a negative voltage supply.
> --
> Greg
>
> Rick C. wrote:
> >I'll poke around and see if can a schematic. The one I have in mind uses
> >two opamps.
> >Rick
> >
> >Richard Sloan wrote:
> >
> > >  >>  A couple more things need to be known before anyone can really
> > give you an
> > >  >>  answer.
> > >  >>  1) Are we assuming p-p freq. to be within audio range?
> > >
> > > any freq, we are dealing with audio range freq however, so it should
> > work for 20-15k range
> > >
> > >  >>  2) How long does the LED have to sustain after receiving threshold?
> > >
> > > well could just blink for the instant it happens, might be nice to have
> > it stay on for 0.25 - 0.5s
> > >
> > >  >>  3) Are you planning to use a PIC to do the detecting? (overkill
> > really)
> > >
> > > no opamp / comparator
> > >
> > >  >>  4) Do you want to detect on > +.2 and/or -.2v?
> > >
> > > yes
> > >
> > >  >>  5) We need to know if you are wanting to mix analog with digital to
> > >  >>  achieve your goal, or straight analog citcuitry.
> > >
> > > hopefully its just analog
> > >
> > >  >>  There are many sample circuits in the National Linear Databooks and
> > >  >>  application notes that will probably provide what you want. A simple
> > >  >>  opamp will achieve your
> > >  >>  desired results. A Norton Amp such as the LM3900 will probably
> > work and
> > >  >>  will operate from 4v to 36v single ended supply. You'll have to dig
> > >  >>  around for a sample
> > >  >>  circuit in the databooks, but they're there. Otherwise someone on
> > the list
> > >  >>  might be patient enough to walk you through a working circuit.
> > >
> > > I have looked and seen non in national book.... i can look again!
> > >
> > > And I agree on patience as question after  question on here needs
> > answering and you could have a full time job just answering!
> > >
> > > Thanks!
> > >
> >
> >--
> >http://www.piclist.com hint: The PICList is archived three different
> >ways.  See http://www.piclist.com/#archives for details.
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.

--
http://www.piclist.com hint: The PICList is archived three different
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