Thus, It begins anew; no Operational Amplifiers for you

Woke up late this morning.  Fortunately, an hour late for me is still 6:52, and I made it to class on time. Even had time to shower, make coffee, wash dishes, and run a wet swiffer my bathroom's (presumably fake) hardwood floors.  Unfortunately I didn't have time for a walk.  Or to shave.  It was a good and hairy morning, nevertheless.

To school I travelled, and to class I went.  Upon entering the room, Mason met my eyes.  His beard bristled in indication of his anticipation for another day of excellent engineering.  His eyes teemed with knowledge waiting to be shared.  The knowledge of a new world unbeknownst to most non-engineers.  This was the world of XKCD comics.  He made a joke about sociologists. We did a simple inverting op amp example circuit.  And Mason saw that it was science.
We did a one of these, calculated gains, noted voltage rails.

Alex made a diagram.  We watched with admiration.


We did a one of these, and did nodal analysis.  There was a significant moment where we realized that the voltage on both inputs of the Op amp is about zero.





Then we were instructed in the summing amplifier.  The equation for this is simply the sum of those three Voltages over their respective resistances.  So, as the middle equations notes, Vout is the sum of the voltages if R1=R2=R3=..., times the ratio of Rf to Rin.

Lab 1 of 2
Summing Op Amp
We select R1 = R2, and use the inverting equation from above.  Values and measurements below:

We talked about another amplifier.  It had 4 resistors of non-equal resistances, and was anything but simple.  Difference amplifier.  Complication equation. If R3=R1, R2=R4, the equation gets much better.  If all are equal, then the output is simply the difference.

Lab 2: Difference Amplifier

Select R1=R3=10kOhm, R2=R4=21.5kOhm

Replace R3 with R2 in the below equation: