# Waveform Generator Problem

Discussion in 'Homework Help' started by callum2510, Sep 7, 2015.

1. ### callum2510 Thread Starter New Member

Aug 26, 2015
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Hi, Just looking for some verification if I have complete this correctly? I'm not 100% sure on my solution.

2. ### WBahn Moderator

Mar 31, 2012
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It is incorrect to say that the inputs of the first opamp are at virtual ground. The term "virtual ground" means that the voltage is 0V (i.e., the same voltage as your "ground") even though that node isn't connected to ground. That is not the case here. These two nodes can be at a voltage other than 0V, but they have to be at the same voltage even though they are not connected to each other. This is known as a "virtual short". The distinction is important.

Feb 19, 2010
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4. ### shteii01 AAC Fanatic!

Feb 19, 2010
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I got C1=0.1 uF.

5. ### callum2510 Thread Starter New Member

Aug 26, 2015
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Do you mind me asking how you got that?

6. ### MikeML AAC Fanatic!

Oct 2, 2009
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That is not correct either. The first opamp is acting as a multivibrator, so the inputs are almost never at the same voltage...

Last edited: Sep 7, 2015
7. ### shteii01 AAC Fanatic!

Feb 19, 2010
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$
f=\frac{1}{T}
T=\frac{1}{f}
f=82 Hz
$

Find T.

T is known.
R3 is known.
Find B.
Plug everything in and solve for C1.
$
T=2*tau*ln(\frac{1+B}{1-B})
tau=R_{3}*C_{1}
B=\frac{R_{1}}{R_{1}+R_{2}}
$

Last edited: Sep 10, 2015
callum2510 likes this.
8. ### crutschow Expert

Mar 14, 2008
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That's true if the op amp is operating in the linear mode but here it's operating as a comparator in a square-wave relaxation oscillator circuit, so the two inputs are only at the same voltage at the instant the output changes state.

Edit: Okay, Mike beat me to it.

9. ### WBahn Moderator

Mar 31, 2012
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Hello! Homework HELP!

10. ### WBahn Moderator

Mar 31, 2012
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True. I didn't consider the circuit beyond seeing the notation -- only had a few seconds to make a reply when I got called away.

11. ### WBahn Moderator

Mar 31, 2012
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Wouldn't it be even more helpful if you wrote up the entire solution and submitted it for the TS?

12. ### shteii01 AAC Fanatic!

Feb 19, 2010
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The dude is too clueless. Me solving this one little problem is not going to make him finish that class with an A. I will be very surprised if the dude can get a B for this class. My bet is on C or D.

13. ### callum2510 Thread Starter New Member

Aug 26, 2015
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Last edited: Sep 9, 2015
14. ### callum2510 Thread Starter New Member

Aug 26, 2015
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I wasn't looking for a answer more an explanation. Why have a homework help section on the forum if you ***** are going to criticize me asking for some help?!

Last edited by a moderator: Sep 9, 2015
15. ### callum2510 Thread Starter New Member

Aug 26, 2015
9
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How the **** would you know what my academics capabilities are? Yes some questions are challenging for others hence why I approached this forum for clarification. You're just an old American wanker that loves to assume stuff without any knowledge

Last edited by a moderator: Sep 9, 2015
16. ### WBahn Moderator

Mar 31, 2012
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Watch the language -- that will get you banned pretty quickly.

I wasn't criticizing you at all -- I was making remarks aims at shteii01 (i.e., the person whose post I was responding to).

17. ### WBahn Moderator

Mar 31, 2012
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The you are always free to go elsewhere. But obscene language won't be tolerated here.

18. ### JoeJester AAC Fanatic!

Apr 26, 2005
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You thanked shteii01 and then quoted his post with no other comments.

Then you went on a rant.

Is there a question forthcoming?

19. ### shteii01 AAC Fanatic!

Feb 19, 2010
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Look. I was responding to WBahn.

Generally speaking, I was rude to callum2510. I admit it. So his response does not surprise me. However! I was rude. He was rude. I got what I deserved. The original question/homework problem was answered. Lock this thread and let us all move on.

Apr 26, 2005
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