Hysteresis for comparator.

W@ldur · 14th January 2006, 09:30 AM

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

peranders · 14th January 2006, 10:36 AM

You can build a peak detector.

W@ldur · 14th January 2006, 11:16 AM

no need for a peak detektor, I only want short flash into a longer "burning".
time relay or smtg.

jackinnj · 14th January 2006, 01:10 PM

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.

davidsrsb · 14th January 2006, 02:54 PM

You need a monostable to stretch the pulses to seconds.

W@ldur · 14th January 2006, 11:41 PM

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.

14th January 2006, 09:30 AM	#1
W@ldur diyAudio Member Join Date: Sep 2004 Location: In speakerbox	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

14th January 2006, 10:36 AM	#2
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	You can build a peak detector. __________________ /Per-Anders (my first name) or P-A as my friends call me Tube Buffered Gainclone in work \|Thread

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14th January 2006, 11:16 AM	#3
W@ldur diyAudio Member Join Date: Sep 2004 Location: In speakerbox	no need for a peak detektor, I only want short flash into a longer "burning". time relay or smtg.

14th January 2006, 01:10 PM	#4
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	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.

14th January 2006, 02:54 PM	#5
davidsrsb diyAudio Member Join Date: Dec 2005 Location: Kuala Lumpur	You need a monostable to stretch the pulses to seconds.

14th January 2006, 11:41 PM	#6
W@ldur diyAudio Member Join Date: Sep 2004 Location: In speakerbox	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.