multiple voltage levels comparison

A

AttO

New Member

• Apr 27, 2009

• #1

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

• Apr 27, 2009

• #2

Post a circuit

 

Sceadwian

Banned

• Apr 27, 2009

• #3

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

 

A

AttO

New Member

• Apr 30, 2009

• #4

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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Last edited: Apr 30, 2009

Sceadwian

Banned

• Apr 30, 2009

• #5

You posted no schematic.

 

A

AttO

New Member

• May 1, 2009

• #6

i've edited the post

 

ericgibbs

Well-Known Member

Most Helpful Member

• May 1, 2009

• #7

AttO said:

i've edited the post

Click to expand...

hi,
Have you seen the LM3914 datasheet.?

 

A

AttO

New Member

• May 2, 2009

• #8

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

 

Last edited: May 2, 2009

A

AttO

New Member

• May 3, 2009

• #9

No more help for me???