Electronic – Connecting AND Gate Chip to an Integrated Circuit

Given the goals of the class, I think the TTL approach is fine, and I say this as an "FPGA guy". FPGAs are a sea of logic and you can do all sorts of fun stuff with them, but there's only so much that's humanly possible to do in a semester.

Looking at your syllabus, your class is a mix of the logic design and "machine structures" courses I took in undergrad. (Plus, it's for CS majors. I'm all for CS majors having to face real hardware--letting them get away with writing code seems like a step back.) At this introductory level, where you're going over how assembly instructions are broken down, I see no real benefit to having students do things in code versus by hand. Doing HDL means learning the HDL, learning how to write synthesizable HDL, and learning the IDE. This is a lot more conceptual complexity and re-abstraction. Plus you have to deal with software issues.

Generally the point of a course that uses FPGAs is to practice creating logic that is useful--useful for talking to peripherals, serial comms, RAM, video generators, etc. This is valuable knowledge to have, but it seems very much out of the scope of your course. More advanced classes in computer architecture have students implement sophisticated CPUs in FPGAs, but again, this seems out of the scope of your course.

I would at the very least devote a lecture to FPGAs. Run through a few demos with a dev board and show them the workflow. Since you're at Mills, perhaps you could contact the folks at Berkeley who run CS150/152 and go see how they do things.

It is conventional to draw circuits so signals flow from left to right, like so:

^{simulate this circuit – Schematic created using CircuitLab}

(You need a base resistor, R3, to limit base current, and a resistor from base to ground to ensure that the transistor does turn off when the switch is open)

With the switch open, the base will be held at ground by R4, so no current will flow through the transistor, so the collector will rise to a voltage determined by R1, R2, and the 2 volts or so voltage drop in the LED - this will allow current to flow through the LED and light it.

With the switch closed, the base will be pulled up, allowing current to flow through the transistor. If the resistors are selected correctly the transistor will be saturated, pulling the collector down to about 0.2 volts. As the LED requires about 2 volts across it, it will not pass any current.

I really dislike the sentence "Current always takes the path of least resistance", as many beginners seem to read it as "Current takes only the path of least resistance". In face, an electric current takes all possible paths, withthe lower resistance paths passing higher currents than the higher resistance paths.