[sdiy] The PPPPPulser

[Grant Richter]

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.