Hello everyone,

I hesitated to post in this section because I couldn't determine if it was more appropriate to post it in the project sections or in the homework. Since this is a relatively simple project and counts as homework, I posted it here. However if I am posting in the wrong section I apologize in advance to the mod team.

I am currently a student in electrical engineering, sophomore. The project is to make an analog computer that solves 2nd order differential equations, with a feedback system.

For the 1st week, we had to build the system in multisim and run the simulation (for pre-experiment report) then make some simple measurements like Vmax and settling time.

I managed the first week to design and run simulation (please refer to attachment) of the system, as well as build it on the breadboard and check the output on the oscilloscope.

Now, for the 2nd week, we are asked to add a feedback circuit to the system. Here, I wasn't quite sure about what to do. Following the diagram, and from what I understood, I need a summer op-amp that will sum the amplified integrated output, with the step function source, to be the new input to the system ?

Well, if someone could please tell me if my assumptions are right, and if so, if the circuit is right.

Thank you !

Attachments :
doc file : description of the project and instructions.
week1.png : my system design.
week2.png : my designed system + feedback design.

 

Is that .doc file an official problem announcement from your school written originally in english? If so, you should really question your professor's credibility. It's english is awful.

As far as the exercise is concerned, I would feel safer if you added all of the feedbacks a, b and z in a summer OpAmp in the leftmost part of the screen.

I don't find any use in U5 in the current implementation. You are not asked to scale the input with a non-inverting OpAmp. Instead use it to sum the three input feedbacks. That would mean that you don't need to send the feedback 'b' directly to the input of U1 and feedback 'a' would have a dedicated inverting OpAmp going to the summer instead of a simple resistance R2 which isn't really feedback.

I think you pretty much nailed the feedback part. A differentiator is all that it seems to be asked for.

Correct me if I got part of your effort wrong.

 

... I need a summer op-amp that will sum the amplified integrated output

I think you just gave nbw an idea for his next cartoon. I can already see that opamp sitting on the beach, sipping a pina colada.

http://forum.allaboutcircuits.com/showthread.php?t=54873

 

Is that .doc file an official problem announcement from your school written originally in english? If so, you should really question your professor's credibility. It's english is awful.

My EE Department is part of a famous college in South Korea - while the professors are usually very good (Circuits I professor got many times awards from IEEE), got their PhDs in American and speak perfect English, the TA (who are in charge of the labs !) are usually grad students not really fluent in English...so the assignment was written in Korean and probably translated used Google that's why I am kind of having trouble with my labs...the instructions are not always clear and very often I don't understand the purpose of the experiment.

As far as the exercise is concerned, I would feel safer if you added all of the feedbacks a, b and z in a summer OpAmp in the leftmost part of the screen.

I don't find any use in U5 in the current implementation. You are not asked to scale the input with a non-inverting OpAmp. Instead use it to sum the three input feedbacks. That would mean that you don't need to send the feedback 'b' directly to the input of U1 and feedback 'a' would have a dedicated inverting OpAmp going to the summer instead of a simple resistance R2 which isn't really feedback.

I think you pretty much nailed the feedback part. A differentiator is all that it seems to be asked for.

Actually if you see the two diagrams, I had to add the z feedback (diagram 2) to the "system" circuit (diagram 1) , so after I checked with the TA today, I got full mark on this The U5 is mandatory because the question was to make u = x - z and only another Op-Amp could have done that (the way I made it).

So yes, basically what they wanted is what I designed.

Thank you a lot for your answer and your...feedback . I hope this post helps students or anyone wanting to build a 2nd order differential equation by using an analog computer.