Kirchoff's Laws

[seastate]

There have been many placeholder chapters from when I first created the IntroSensors.tex document. Chapters then roughly reflected handouts/activities/weeks in my course.

For example, the thermistor calibration activites are part of CircuitsIntro, and this chapter is now redundant.

I had listed a chapter (CircuitDesign.tex) on Kirchhof's Laws etc.

This seems very important and should be somewhere in the book. But I'm not sure it has enough content to be in a separate chapter.

In my class, all we really did (beyond resistors in series) was work a little with resistors in parallel in a thermistor circuit -- pretty much just an excuse to use parallel resistors and Kirchhof's Laws.

A more meaningful application might be a Wheatstone bridge, e.g. with a strain gauge, or hot wire anemometer, or...?

There is a placeholder now for a strain gauge activity, in the chapter on Environmental effects on electrical characteristics. So Kirchhof's Laws could go there. However, that seems a low-visibility place for an important topic.

Alternatively, Kirchhof's Laws and a simple application could go in Environmental sensing with voltage, current & resistance. That fits conceptually but risks becoming a long unwieldy chapter.

(BTW I have the sense that the title of this chapter should include time, but I don't know a way to fit that in without it sounding cumbersome).

Another possibility is to break out the voltage/current/resistance content and the time-based content (so far, light frequency & the acoustic distance sensor) into two shorter more focused chapters.

The latter scheme just occurred to me, so I haven't though much about it. But at first glance it seems appealing to me.

What do you think?

[jwlauer]

I never specifically covered Kirchoff's laws, but I started down that direction in the chapter where I cover voltage and current measurements. I tried to limit the discussion to resistor dividers, and even then, the section got pretty long. I'm not sure we need to talk too much about networks--I image most users of the text will be interfacing with digital sensors anyway. But I think you are right that something on strain measurements (and thus Wheatstone Bridges) would be nice (same with hot wire anemometers), and I guess I kind of agree that would be the place to cover Kirchoff's laws, if they even show up under that name in the text.

All that said, we could introduce the concept of parallel loops at the end of the section on voltage measurement, in the context of the CTD. It is debatable whether the EC sensor should be connected in parallel with the thermistor (which reduces the number of GPIO and ADC pins needed) or if it's better to connect it to it's own GPIO pins . If in parallel, the circuit is really a network with two loops. Maybe maybe simply discussing the relative merits of each approach would be enough for an introduction.

I think it's good to break out the voltage/current/resistance from time. Fundamentally, time is closely related to capacitance anyway--c.f. the concept of an RC circuit's time constant. I don't think you would need to change the order of exercises in the book in order to handle frequency or time-based measurements differently. It's still fine to cover timestamps and their accuracy first, then talk about voltage, then talk about time/frequency and maybe capacitance.

I also think we have to be careful not to go too deeply into AC circuit analysis. When I suggest covering RC behavior, I'm only suggesting a brief discussion of capacitor charge/discharge cycles and how these can produce a frequency output that varies with an electrical signal. I'm not suggesting analysis.