@Circuitfantasist Well, my suggestion on Covid Cough Signal Analysizer is for your students, perhaps supervised by you and/or your teaching colleagues. For you invention passion in circuits, it would be nice if you can make them or suggest how to make them as a practical engineering useful in real life, as I am saying, helping to fight against Covid19.

@Circuitfantasist But I watched the video by Dave Jones and found it very good to explain most of the basic things about op amp. His two fundamental rules of op amp, and the idea of "virtual ground" is very good. On the other hand you circuit diagram is a bit messy. So I think your students won't be that impressed. Perahps you can also make a youtube video to explain you ideas.

@tlfong01, I don't know why but I can't reply to a specific message from my phone... OK, let's begin from your last message. Regarding Dave's movie... It's a big show with a lot of words and gestures, something like a Hollywood movie. He says many things but explains almost nothing ... or he does it on the usual formal level...

In other words, "Much Ado About Nothing"... But I have watched it briefly... OK, I will watch it to see if there is something different in its content (not the form) than the usual web texts...

My circuit diagrams look "a bit messy" because my goal is to provoke student's (reader's) creative thinking. If I had time and space enough to expose my idea (because I always have an idea to explan), you (readers) would understand all. This can't happen here in SE EE but I have done it on my site, in Wikibooks and ResearchGate...

The true understanding of circuit ideas requires a very good contact with the person you are explaining to and goodwill on his/her part (what is missing here). My students always understand my explanations in the lecture hall and the laboratory because there is a very direct connection between them and me… and I don't stop explaining until I'm sure they understand me.

I will share a wisdom with you because you are benevolent and want to understand my way of thinking. It reads as follows: To truly understand the idea behind ​​a circuit, you need to know where the currents flow inside it. Each current starts from the positive terminal of the power supply and returns there to its negative terminal. That is why I present the currents with their full loops (in green, from the association with running water).

Also, to truly understand the idea behind ​​a circuit, you need to know what the voltages across its elements are the connection between them. That is why, I present voltages "geometrically" by voltage bars (in red). They can be easily summed according to KVL thus showing the relation between them...

This geometric way of presentation is much more visual than the digital way used in simulation programs with very varying digits after the decimal point... which is meaningless for the purposes of understanding.