[sdiy] Help with lm339

[Brock Russell]

At 09:48 AM 4/1/2006, you wrote:
>I am trying to use a lm339 comparitor to determine when an ADSR signal
>reaches the sustain level.  What I want to do is add a small voltage
>to the sustain level voltage so that the comparator fires just above
>when the envelope reaches it (if I don't do this, it just waffles
>around when the two voltages are equal ie:when the envelope is
>sustaining).  Is there a simple way to do this (without adding a
>summing opamp)?

Hysteresis. Basically it changes the input level after the trip point is 
attained.

http://www.national.com/an/AN/AN-74.pdf page 4
http://www.maxim-ic.com/appnotes.cfm/appnote_number/3616