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Old 14th January 2006, 09:30 AM   #1
W@ldur is offline W@ldur  Estonia
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Default Hysteresis for comparator.

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
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Old 14th January 2006, 10:36 AM   #2
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You can build a peak detector.
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Old 14th January 2006, 11:16 AM   #3
W@ldur is offline W@ldur  Estonia
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no need for a peak detektor, I only want short flash into a longer "burning".
time relay or smtg.
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Old 14th January 2006, 01:10 PM   #4
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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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Old 14th January 2006, 02:54 PM   #5
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You need a monostable to stretch the pulses to seconds.
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Old 14th January 2006, 11:41 PM   #6
W@ldur is offline W@ldur  Estonia
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problem solved.

between input and comparator a diode. from comp. input a 47uF lyt. to GND and parallel with it a 100k potensiometer.

really, it works.

it is called signal intergrating or smtnh like that.
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