[sdiy] Question for the sages...

[CHoaglin at aol.com]

In a message dated 5/4/01 5:53:41 PM Pacific Daylight Time, chris at smg.org 
writes:

<< I have a rather mundane question, but (like all my previous questions) one
 that is probably easily answered. Is there such thing as a simple circuit
 wherein you have an input for a control voltage, and (say...) a
 potentiometer for setting a split point, where all voltages over that point
 are sent out one output, and all voltages under that point are sent to a
 second output?
 
 This seems like such a simple (and usefull) concept for a module, but I
 can't for the life of me find a module or example circuit that does such a
 thing, which leads me to believe that it's not simple at all. Thanks in
 advance for any help on this matter.
  >>

It sounds like a job for a garden variety comaparator to me...use the pot to 
set the threshold at which the output swings, and drive the base of an NPN 
transistor with that, which routes the signal through it to one destination, 
as well as driving a PNP transistor which cuts off the signal path to the 
other destination. Input voltage below threshold=PNP transistor conducting, 
signal fed to first output. Input voltage above threshold=comparator output 
goes high, NPN transistor conducts, PNP stops conducting, signal fed to 
second output...at least that's the first thing I thought of. Maybe someone 
more experienced can think of something better?

Chris