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multiple voltage levels comparison

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AttO

New Member
I want to make a circuit that is able to differentiate between 4 different voltages, if the input is 5volts, one led let, if 7volts, two leds let,... etc
i tried to make it using 4 comparators but when i test every one separately it works fine, but when i put the input (5 or 7 or...) to the 4 comparators all led let regardless the input value, and some times!!!
i'm supplying the op-amps with +ve 15 and -ve 15, i placed a diode on the comparator o/p to neglect the -ve output

Please help...
thanks
 

MikeMl

Well-Known Member
Most Helpful Member
Post a circuit
 

Sceadwian

Banned
You would use an opamp as a voltage follow and the output of the opamp would go to the comparators. If you've done this post the entire schematic of what you have so far
 

AttO

New Member
this is the circuit i tried.
Please note the following:

The diode id to assure no -ve signal go to the 555
the resistors before and after diode one as pullup resistor, the other is pulldown. i tried with and without the diode and two resistors but the problem is the same.

I didn't got what you mean by using opamp as voltage follower the to a comparator you want me to make a buffer before comparison??, if so, how will that help.
thanks and sorry for delay
 

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Sceadwian

Banned
You posted no schematic.
 

AttO

New Member
yes, ericgibbs.. thanks but i'm testing a capacitor discharge , so. the input duration is about 10ms only. thats why i need the monostable cct to prolong the time of output display
 
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