op amp circuit that calculates grade percentage of a subject

Thread Starter

thedarkpty

Joined Nov 25, 2022
5
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.

16693915834591347555422702855228.jpg
 
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ericgibbs

Joined Jan 29, 2010
16,792
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. ;)
 
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WBahn

Joined Mar 31, 2012
27,893
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
27,893
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?
 

crutschow

Joined Mar 14, 2008
31,126
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.
 
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