[sdiy] The PPPPPulser

[jhaible]

Hi Grant,

yes, in your example the LEDs are performing the logical function
output_N and not output_N+1 all by themselves, because they are
floating.

JH.

-----Ursprüngliche Nachricht-----
Von: Grant Richter <grichter at asapnet.net>
An: jhaible <jhaible at debitel.net>; <synth-diy at dropmix.xs4all.nl>; Ian Fritz
<ijfritz at earthlink.net>
Gesendet: Sonntag, 8. Juni 2003 22:48
Betreff: Re: [sdiy] The PPPPPulser


> Hello Jurgen,
> >
> > I have a similar circuit, built from LM339 quad comparators, in
> > my JH-720:
> > http://home.debitel.net/user/jhaible/jh_720_vco_scanner.gif
> >
> >
> > As an ordinary comparator chain produces a "bar" rather than a
> > "dot" code, I had to find a way to convert the bar to dot.
> > At first I thought about some logic after the comparator outputs,
> > but as I'm also only taking every second output (to get that
> > multiple pulse waveform), I could simply wire the comparator
> > outputs together in pairs, with the comparator inputs having
> > opposite polarity. As we're going up the "thermometer code",
> > the first comparator of a pair "sets" the dot, and the second
> > "clears" it. Then the same thing will start again with the next pair
> > of comparators.
> >
>
> This trick may interest you, while not immediately applicable to your
> circuit, I was reminded of it by the string of LM339s.
>
> It produces a "dot" node with LM339s driving LEDs using only a single
> section. Consider a stack of LM339 comparators in a bargraph circuit using
> LEDs in series with current limiting resistors from the plus rail.
>
> If you use a diode to connect the next higher stage OC to the plus side of
> the LED below it, the OC will not only turn ON the LED for that stage, but
> shunt the current from the plus side of the LED below it, turning the LED
> below OFF.
>
> So adding 3 diodes will turn a 4 comparator "bar" into a "dot" display by
> current shunting.
>
>
>