Hysteresis for comparator.

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I built a comparator using TL074, actually 1/4 of that.

everything works!
when I send audiosignal into comparator, LED will flach according to the signal.
but it flashes too fast. I want it to flash not so much-I want it to work for 30seconds after it has light once.

signal comes for 1/2 seconds, led works for 30secs.

can i do it adding a hysteresis to comparator or I have to add some transistor ana capacitor as well?


Thanx..

W@ldur
 
hysteresis reduces a comparator's susceptibility to noise, eliminating false triggering.

what you really want to do is add a time constant to one of the inputs of the comparator -- V = E^-(t/RC) -- then you have to figure a way of discharging the capacitor as the input impedance is not low enough to drain it.

take a look at Rod Elliot's VU meter project and you'll get the general idea.
 
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