[sdiy] The PPPPPulser

[Ian Fritz]

Hi All --

I took an hour yesterday and white-boarded the variable multi pulser I 
proposed a while ago.  To review, it uses an LM3914 bar graph chip with a 
constant (0-1V) saw drive and a variable (5-.5V) control drive on the 
comparitor resistor chain.  The odd-numbered 3914 outputs are summed into a 
comparitor to make a pulse train. The output starts out as a square wave 
and continuously adds more pulses, up to five, as the external CV varies 
from 0 to 5V.  The whole circuit just takes the 3914 and two op amps.

The results are pretty interesting, I think.  The unit actually has a lot 
of the characteristics of a filter.  There is a lot of phase shifting going 
on, along with large and rapid changes in the harmonic content.  A sweep 
through control voltages sounds somewhat similar to a sweep of a high-Q 
bandpass filter.  Here's an MP3 demo, which is just a sweep up and down in 
CV, with no other processing.
http://home.earthlink.net/~ijfritz/xfer.htm


   Ian