Re: SSTC Singing Arc Design - Help needed

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


There are a raft of voltage to frequency converter chips out there...

Dave's comment about heavily embedded FM chips is well taken.  Most cheap 
FM modulators (i.e. "mr mike") at RF use something like direct modulation 
of a varactor in a LC oscillator.  FM generators at lowish frequencies are 
very unusual (large percentage bandwidth for one thing).



At 11:37 AM 9/12/2002 -0600, you wrote:
>Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><davep-at-quik-dot-com>
>
>
> >     You might try the following:
> >     Run your audio signal through a comparator (zero crossing detector) so
> > you have a rough square wave version of the original audio. Use this signal
> > to trigger a fixed pulse width one shot (say, 20uS or whatever your current
> > maximum pulse width is with your TL494. You can make this circuit with a
> > '741 op-amp and a 74HC4538. This gives you a bunch of 50uS drive pulses at
> > the audio rate.
>
>         Thought:
>         (May have been covered, may not be applicable):
>         'simply' (chips are available) FM the audio.
>         FM is a quasi digital mode....  (I've not looked: all
>         the FM chipsets may be too heavily embedded, or with
>         too high an output freq to be useful...
>
>         best
>         dwp
>
>...the net of a million lies...
>         Vernor Vinge
>There are Many Web Sites which Say Many Things.
>         -me