[sdiy] The PPPPPulser

[Ian Fritz]

At 01:43 PM 6/8/2003, jhaible wrote:

>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

Very interesting.  I hadn't seen that before.  So it's a PPPPPPulser.
:-)

>I've used a 3080 to control the input level. Your method
>of applying a variable Voltage to the resistor divider chain
>is certainly more elegant!
>
>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.

Ah, very clever how you did that.  I always pictured this as being more 
complicated, which is why I stuck with the 3914.  Your configuration seems 
quite versatile -- you could easily set separate amplitudes for the 
different pulses, or vary the input comparitor levels, etc.

>Of course these LED driver chips have all the required logic
>already built-in. But if someone is looking for a "standard chip"
>version, you may find the LM339 version interesting.

Either way, I think it's a really great waveform generator.  Pulse trains 
are underappreciated.  Here's an older synth based on pulse-train technology.

http://www.variophon.de/index_e.htm

   Ian