# Plotting expected output for an inverting adder??

Discussion in 'Homework Help' started by dmkk09, Oct 9, 2010.

1. ### dmkk09 Thread Starter New Member

Oct 7, 2010
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0
The inverting adder has the following component values R1 = 10Kohm R2 = 100Kohm Rf = 100Kohm V1 = 100sin2000(pi)(t) mV V2 = 2V V3 = 0 plot expected output for 0<t<2mS

I have derived the voltage eq to be V0 = -Rf (V1/R1 + V2/R2 + V3/R3) plugging in values i got V0 to be -2.29 V how can i plot this??

2. ### Georacer Moderator

Nov 25, 2009
5,154
1,280
You forgot to give a value for the R3 resistance, not that it makes a difference...
Whate makes a difference is that the output is not a DC waveform of -2.29V, but it has an AC sine wave on top of it, caused by the V1 input voltage.

What is it that you want to plot? The output waveform? If so, you could try a free simulation software that will do the analysis for you as well as plot the output. PSpice is one of many, simple but basic format and interface.
If you want to skip the trouble and just plot the outcome, http://www.wolframalpha.com/ will do it for you if you give it the formula of the function you want to plot. In this case y=Va+Vbsin(wt). Replace with numbers, and presto! you have it.

3. ### dmkk09 Thread Starter New Member

Oct 7, 2010
4
0
Hello georacer Would i be right in Assuming that Va = V1 and Vb = V2? With the equation would i enter increments of t (0<t<2mS) to generate the plot?? Also i used t = 1/f and w = 2(pi)(f) to get the angular frequency values is this correct??

Oct 7, 2010
4
0
5. ### Georacer Moderator

Nov 25, 2009
5,154
1,280
Do not assume things. Take every step with caution. You had the initial formula right. Vo=-Rf(V1/R1+V2/R2+V3/R3), and you know all your variables. You know all the resistances (R) and all the input signals (V). Replace the variables with their actual value and let us know what you found.

6. ### dmkk09 Thread Starter New Member

Oct 7, 2010
4
0
Yes i got -0.289t - 2

7. ### Georacer Moderator

Nov 25, 2009
5,154
1,280
Not at all! For V1 substitute the whole sine. Where V1 replace it with $100 \cdot \sin(2000 \pi t) mV!

Try it once more and write down the steps too, so that we point out where you go wrong (if you do this time).$