# Op amp learning

I teach electrical engineering and during 5 weeks, we cover the basics of op-amp. However, I felt that there wasn't enough content since I had a lot of time for review before the exam.

On a theoretical level we cover:

• Derivation of the gain equation for inverting and non inverting op-amp
• Op amp golden rule (try to maintain v+ and v- balanced and no current enter the op-amp input)
• Quick calculation for summing amp and differentiator topology.
• Comparator
• Gain
• Saturation voltage

On a practical level, we do different circuits based on the theory.

My question is: what is the next logical step if I want to push a bit more? My current choices are: GBW, slew rate or simply add another topology. keep in mind that it is an introductory course for technicians and that they mostly do industrial work once out of the school.

If you have any interesting circuits that you had more fun doing within a 2 or 4 hour time frame, I can also look at that. My end goal is to push a bit more and make my labs a bit more interesting.

• To make interesting, do a control system for something physical on a toy scale. Self balancing robots are possible, especially if you cheat in providing a black box to translate inputs and output from the more available digital sensors and actuators to host an analog control system in the middle. Or just gut RC hobby servos bringing out the motor and feeback wires, put big pointers and clock faces on them and build systems to make them track a potentiometer as it's manually turned. Aug 14, 2018 at 20:56
• Use the Falstad simulator to simulate the transfer function of car with softer springs but a variable hydraulic suspension to limit travel and g level of the ride using PID feedback. Aug 14, 2018 at 21:14
• Make a triangle square generator with variable frequency. Using hysteresis and negative feedback in 2 stages . Then buffer with PNP-NPN Darlingtons inside the loop to drive a speaker or a woofer or a small DC motor at very low frequencies with tri-level square wave which approximates a sine or make a very low f sine , vbl amplitude motor oscillator Aug 14, 2018 at 21:26
• Very important - to identify when an amp is working like an amp (v- ~ v+ and golden rule applies), and when it's not (comparator or relaxation oscillator, or in saturation) Aug 15, 2018 at 6:40
• One of my 1st OpAmp labs in Uni was a staircase generator , the GE app note schematic had a fault and I was the only student that got it to work. Aug 15, 2018 at 17:39

Before be an engineer, I was also an electronics technician. In a similar way to the course that you teach, the objective of my one was to enable technicians for the industrial segment. Our discipline was about linear and non-linear applications of Op. Amps. For the former case, for example, are the voltage follower, current sources, current amplifiers, voltage regulators and DA converter. A good topic to address are the single supply power configurations (avoiding CMR violation). For the later case (important for the industrial area) are the Schimitt-Trigger, waveform generators - square and triangular, window comparators, etc. A good topic to address is the internal (simplified) model of 555 IC. In the mid are the precision rectifiers.

EDIT

As a practical example of waveform generation with "some" additional glue, consider the high level circuit shown below. This is a way to generate a simple lighting pattern for a water fountain. The figure shows three LEDs (R, G, and B), but my original design drove three 12V high current water-proof incandescent bulbs (one 127Vac/12Vac transformer, three TCA785 ICs and three TRIACs completed the circuit). The complementary E1 and E2 (staircase) inputs are produced by means of 555 oscillator, one R2R network (D/A converter) and two LM324 op. amps. The switches S1 to S6 are implemented with 4066 analog switches. A set of flip-flops and logic gates (mealy machine) generates the signals for 4066's. The challenge was not to use microcontrollers twenty years ago.

• oh waveform generators, that is a good one indeed! Schmitt trigger is also extremely useful even tho people will classically use a dedicated IC for that. Your answer is quite insightful based on your background as well. Aug 15, 2018 at 1:34

I like the classic LM324 VCO circuit. It illustrates the integrator principle and you can make a audio-range VCO with it, which is one of the building blocks of a synthesizer. If you have an amplifier + speaker it's a nice change from the usual blinking LED demos.

• While I might do it for my personal fun, it is a tad bit too much on the complexity level for them. Maybe like a bonus or something could be applicable. Aug 15, 2018 at 16:10
• Maybe. It's pretty easy to do on a solderless breadboard. Aug 15, 2018 at 17:30

simulate this circuit – Schematic created using CircuitLab

A simple portable headphone amp using 9V battery. Input is from a source, example from a cell phone. Output connect to the headphone. Let the 470uF charge to 4.5V before plug in the headphone, otherwise there will be pop sound.

• Audio is quite interesting for them since they ''natively'' get the concept of frequency. I could go one step further and ask them to play with filters afterwards...Interesting! Aug 15, 2018 at 16:08