Voltage comparator circuit required

[atifkamal]

I need a simple comparator circuit that can monitor voltage drop and latch a relay for few seconds, i have tried one but input detection part is not working as desired.

Scenario is like i have a output from an alarm clock that is 1.3-1.4 volts, when alarm is activated it fluctuate between 0.9 to 1.3v.



can some one help in this ?

 

[jiripolivka]

Check the data sheet of LM311, a good comparator.

 

[kabeer02]

you can also use LM358 is a good one too

 

[PA4TIM]

LM358 is a double opamp, not a comparator. , LM311 is a comparator

 

[amayilsamy]

Which point you monitor the voltage . Mark that point.
And what is the purpose for measure that voltage.

 

[PA4TIM]

Is the output from the clock you use AC od DC ?
You say it fluctuates, that sounds to me as a measurement related problem. If that is an AC signal (or AC with a DC offset) and you have a "not so good" meter the reading will be wrong in DC mode and if the frequency or crest factor is to high, also wrong in AC mode.

Is this a special DC output or did you use the signal from the speaker ?

Do you have a schematioc from the alarmclock?
Do you have a scope ?

 

[atifkamal]

Thanks friend...

Is the output from the clock you use AC od DC ?
DC, 1.5 volts button type cell.
You say it fluctuates, that sounds to me as a measurement related problem. If that is an AC signal (or AC with a DC offset) and you have a "not so good" meter the reading will be wrong in DC mode and if the frequency or crest factor is to high, also wrong in AC mode.
Yes, I am also thinking in this way, i am measuring output of clock alarm from normal digital multimeter, it could give false results between AC and DC, i would check this on AC scale on meter.

Is this a special DC output or did you use the signal from the speaker ?
I don't think any special output, yes i measured it from piezo buzzer points..

Do you have a schematioc from the alarmclock?
unfortunately No ! its a cheap Chinese brand digital alarm clock
Do you have a scope ?

Nops..

 

[atifkamal]

Which point you monitor the voltage . Mark that point.
And what is the purpose for measure that voltage.

i need to trigger a relay for few seconds when alarm activates, actually need to switch on a load at 11:00 pm