# Help with using OPAs as comparators to decode logic level signals as colored LEDs

#### bozkurtkaan54

Joined Dec 6, 2022
3
MODERATOR NOTE: Thread title changed to something that (probably) approximates the question.

Hi guys. I'm student from Turkey , i can try explain subject.
I have AV and BV , us refferance V = 5 if
A<5 if Red
A>5 if Yellow
B<5 if Red
B>5 if Yellow
green = if A and B RED YELLOW or YELLOW RED
blue = if A and B RED RED or YELLOW YELLOW
I mean we need extra opamp or anything
i add as much as i can

I didnt blue and green led can u explain

Last edited by a moderator:

#### dl324

Joined Mar 30, 2015
17,010
Welcome to AAC!

Please post the complete text of the problem.

LTspice doesn't work well if you don't connect the voltage sources correctly.

#### bozkurtkaan54

Joined Dec 6, 2022
3
Welcome to AAC!

Please post the complete text of the problem.

LTspice doesn't work well if you don't connect the voltage sources correctly.
Sample:
For student number XXXXXXXXAB
Red if A<5
Yellow if A>5
Red if B<5
Yellow if B>5
Green if AB Red Yellow or Yellow Red
Blue if AB Red is Red or Yellow is Yellow
For example, if the student number is XXXXXXXX00, the Red Red Blue LEDs will light up.
is my question

#### crutschow

Joined Mar 14, 2008
34,697
All your sources need a ground connection.
Otherwise there's no place for the source current to go.

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#### WBahn

Joined Mar 31, 2012
30,251
Sample:
For student number XXXXXXXXAB
Red if A<5
Yellow if A>5
Red if B<5
Yellow if B>5
Green if AB Red Yellow or Yellow Red
Blue if AB Red is Red or Yellow is Yellow
For example, if the student number is XXXXXXXX00, the Red Red Blue LEDs will light up.
is my question
It's very hard to tell what you are trying to accomplish.

How many different LEDs do you have?

It sounds like you have two red and two yellow LEDs (one for each of the last two digits of the student number).

What should happen if the digit is equal to 5?

Then do you have a single green and a single blue LED?

How is the student number being presented to the circuit?

"is my question"... what? I don't see any question at all?

Is you question whether anyone here will solve your problem for you?

#### bozkurtkaan54

Joined Dec 6, 2022
3
It's very hard to tell what you are trying to accomplish.

How many different LEDs do you have?

It sounds like you have two red and two yellow LEDs (one for each of the last two digits of the student number).

What should happen if the digit is equal to 5?

Then do you have a single green and a single blue LED?

How is the student number being presented to the circuit?

"is my question"... what? I don't see any question at all?

Is you question whether anyone here will solve your problem for you?
The last 2 digits of our student number give the numbers A and B. For example, if my school number is G210100015, A=1 B=5, but B=6 was taken as nothing was said for the B=5 condition. If the lit leds are of the same color, the blue led will turn on, and if they are of different colours, the green led will be lit.

#### WBahn

Joined Mar 31, 2012
30,251
The last 2 digits of our student number give the numbers A and B. For example, if my school number is G210100015, A=1 B=5, but B=6 was taken as nothing was said for the B=5 condition. If the lit leds are of the same color, the blue led will turn on, and if they are of different colours, the green led will be lit.
And how are A and B presented to the circuit?

Why was B=6 used instead of B=4? It sounds like there is a hole in the problem specification that should be addressed instead of just making something up.