Let's face it: when most students looking think about what “electrical” engineers work on – to the extent they do so at all – they think software, programming, apps, and similar. Designing circuits (what we colloquially and misleadingly refer to as “hardware”) is unlikely to fit into their perception. If they think of electronic circuitry at all, it's probably just processors and memory. It's a good bet that analog circuits and components don't enter into their mental image at all.
Yet the broadening of STEM efforts such as the FIRST robotics program shows that sooner or later, students with almost any sort of EE leanings will need to deal with real-world circuitry. Software alone won't build a successful robot; you need lots of analog, digital, and power components and circuitry for a moving object (plus motors and other mechanical components, of course).
For those who think engineering consists mostly of sitting at a keyboard and writing, modifying, or debugging code, the world of real circuits can be a shock. There's a large mental disconnect between tapping out a few lines of code to control a motor, for example, and truly understanding what actually changes in a circuit's behavior as a result, such as drive voltage and current dynamics versus mechanical response.
That's why I think that for students who have a desire or need to better understand what circuitry and signals are all about, it may make sense to work with basic all-analog circuits. By building, probing, and observing the signals and their changes in these circuits without any code requirements, students can get a real feel for otherwise abstract concepts such as voltage, current, and more. Even better, by changing some component values, they'll have some sense of what that capacitor or resistor does.
I've seen many of non-trivial analog “starter” circuits over the years, and the good ones are easy to build, do something interesting, and also very amenable to basic probing with a voltmeter or basic oscilloscope. They have the needed criteria: no hard-to-obtain components; no critical component parameters; through-hole components with few or no SMT parts; nothing costly; have flexible layout options (soldered or breadboard); and can be easily probed since they are all low-voltage designs.
Among the good ones I have seen are this Lightning Detector and its companion Lightning Simulator (scroll up at same link), both based on basic discrete transistors and passive components. Another nice one was in May 2015 issue of QST, published by the American Radio Relay League (amateur radio), “Key Your Rig Without a Wire” (Table of Contents here; the article itself is not online to non-subscribers). It showed how to use the venerable 555 timer to control a 40-kHz ultrasonic transducer at the transmit side, and use a complementary transducer, 741 op amp, 567 PLL decoder, and 7404 hex inverter at the receive side to effect a contact closure. Very simple, very nice, and the ultrasonic aspect adds some pizzaz.
Speaking of the 555, could there be a better analog instruction vehicle than that IC? Yes, there is: the very reasonably priced “Three Fives” kit from Evil Mad Scientist is a discrete kit version of the 555 timer IC. As a discrete implementation, it allows you to probe all the internal waveforms of that ingenious IC. Once you truly understand those signals, you can go on and build any of the thousands of 555 circuits available online or in various handbooks using the kit or the IC 555—many of which are quite interesting. (They also have an XL741 kit, which is a discrete version of the legendary 741 op amp; it also looks like fun and a potential teaching tool).
As an added benefit, since these projects have lots of static voltage points, students can measure voltages and current with a basic DMM. Going a little further, they can observe waveforms using front ends which transform iPhones into oscilloscopes, such as those from Oscium or the iOS scope, or use standalone scopes such as those discussed by Ken Wyatt in his article “Try an oscilloscope for under $200.” Low-frequency operation relaxes many of the demands on the scope function.
What's your view on good ways to introduce students to real-world circuitry, once they are beyond the standard starter circuit of a battery, some switches, and LEDs used in simple series and parallel circuits?
Caption Figure: The “Three Fives” kit from Evil Mad Scientist is an all-discrete version of the classic 555 timer IC, and allows full access to all the internal waveforms; it's a great tool for insight and understanding. Related links