[sdiy] Help with lm339

[harrybissell]

without seeing your schematic, its tough to give exact advice...
but the usual solution to your problem is to add hysteresis
to the circuit... you need a series resistor in the positive input
and a large value resistor from the output to the positive input.

Hysteresis moves the positive voltage a little bit... so that when the
trip point is reached the signal is suddently moved WELL into the
region and there is no oscillation.  Use a small amount, or you will
create a latch situation.

I did an envelop gen years ago where I chose your proposed solution...
it will work but it is a little complex.

H^) harry

J C 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)?