# op amp circuit that calculates grade percentage of a subject

Thread Starter

#### thedarkpty

Joined Nov 25, 2022
7
Hello, I need to make an op amp circuit that calculates the grade for a subject, where there are 4 types of grade 35% 10% 20% and 35%, within each percentage it is 0-100 points, so I plan to do this :
100%=10mV

Input 0-10mV output 0-3,5mV
Input 0-10mV output 0-1mV
Input 0-10mV output 0-2mV
Input 0-10mV output 0-3,5mV
How can I calculate the values of the resistors so that it gives me the value that I require? and the type of opamp?
Mod: cleaned up your image.

Last edited by a moderator:

#### ericgibbs

Joined Jan 29, 2010
18,835
hi the,
Welcome to AAC,
Is this a typo. 35% 10% 20% and 35%,
E

#### WBahn

Joined Mar 31, 2012
30,038
hi the,
Welcome to AAC,
Is this a typo. 35% 10% 20% and 35%,
E
I'm pretty sure those are the weightings of four different grades -- note that they add to 100%.

#### ericgibbs

Joined Jan 29, 2010
18,835
hi WB.
He has two 35% in his listing, is 5% or 15%.?
E
Added:
the grade for a subject, where there are 4 types of grade 35% 10% 20% and 35%,

Suggests to me just one subject, so why 4 Grades, with two the same.???

@WBahn
Read your post #6, sounds logical, I was following the old Adage, If in Doubt, Ask.

Last edited:

#### WBahn

Joined Mar 31, 2012
30,038
Hello, I need to make an op amp circuit that calculates the grade for a subject, where there are 4 types of grade 35% 10% 20% and 35%, within each percentage it is 0-100 points, so I plan to do this :
100%=10mV

Input 0-10mV output 0-3,5mV
Input 0-10mV output 0-1mV
Input 0-10mV output 0-2mV
Input 0-10mV output 0-3,5mV
How can I calculate the values of the resistors so that it gives me the value that I require? and the type of opamp?
Mod: cleaned up your image.

View attachment 281435
First thing that you need to do is select an opamp that is going to be good enough to work with this cascade of signals with 10 µV accuracy (1% of the grade that's weighted 10%) all the way through.

Why do you want 100% to be represented by 10 mV? Why not 1 V or even 10 V?

Ignoring that, you need to show YOUR best effort to solve the problem. We can then help steer you back on a good path when you go astray.

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#### WBahn

Joined Mar 31, 2012
30,038
hi WB.
He has two 35% in his listing, is 5% or 15%.?
E
Think of it this way:
Homework: 35% of total grade
Quizzes: 10% of total grade
Midterm: 20% of total grade
Final Exam: 35% of total grade

#### crutschow

Joined Mar 14, 2008
34,405
Why are you using such low voltages?

Thread Starter

#### thedarkpty

Joined Nov 25, 2022
7
Why are you using such low voltages?
at first I selected 10v for 100% but they told me that it worked better with mV, idk

Thread Starter

#### thedarkpty

Joined Nov 25, 2022
7
Think of it this way:
Homework: 35% of total grade
Quizzes: 10% of total grade
Midterm: 20% of total grade
Final Exam: 35% of total grade
If that was what i forgot to put

Thread Starter

#### thedarkpty

Joined Nov 25, 2022
7
This is theoretical that is going to be simulated with Multisim

Thread Starter

#### thedarkpty

Joined Nov 25, 2022
7
a clearer picture of my problem

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#### WBahn

Joined Mar 31, 2012
30,038
Still need to see your best attempt?

One thing you might ask yourself is how you can have four different voltages at the same node, like you've shown?

Where did this circuit layout come from?

#### ericgibbs

Joined Jan 29, 2010
18,835
Hi,
I have a draft working circuit, but as WB states, let's see your attempt.
E

#### crutschow

Joined Mar 14, 2008
34,405
Do you know how to calculate the gain of the inverting op amp configurations you have?
If not, do a little research on that subject.