Digital electronics on Chromebooks, one working circuit per unit
- 192parts on the bench
- 25boards running now
- 1.00xreal time, on every board
A high school digital electronics course follows a familiar arc: breadboards and Ohm’s law, logic gates, Boolean algebra and Karnaugh maps, adders, then latches, flip-flops, counters, the 555 timer and finally a microcontroller. This page gives you one circuit for each step. Every one opens in a Chromebook’s browser and runs, built from the chips your students will meet on a real bench.
It is a companion, not a curriculum. The unit names below are generic and follow no publisher’s numbering, and the circuits are ours. Use them for demos, warm-ups, make-up work, or as the build step of an activity you already teach.
The circuit above is the Karnaugh map unit in one picture. A majority function (the output is 1 when at least two of three inputs are 1) simplifies to AB + AC + BC, which factors to AB + C(A + B): two AND gates from a 74HC08 and two OR gates from a 74HC32. Flip the three switches through all eight rows and check the LED against the table. We did, and it lights on exactly the four rows it should.
Breadboards, LEDs and Ohm’s law
Before any logic, students need to read a breadboard: which holes connect, where the rails run, and why an LED needs a resistor. The starter circuit is a switch, a resistor and an LED. Add a multimeter from the parts picker and measure the resistor’s voltage, and Ohm’s law becomes a number they found rather than one they were told.
Logic gates and truth tables
Two buttons feed a real 74HC00 and a real 74HC86. Students fill in both truth tables by pressing, then pull the ground wire off one chip and watch its output go dark rather than read 0. That one experiment explains most of the “my circuit does nothing” moments later in the year.
Boolean algebra and Karnaugh maps
The workflow students practice is truth table, map, groups, expression, then circuit. Mokxi has no Karnaugh map solver yet, so the map stays on paper, where the thinking happens anyway. The build is the check: if the LED disagrees with the truth table on any row, the grouping or the wiring is wrong, and the switches tell you which row.
A good extension: build AB + AC + BC as written, with three ANDs and two ORs, next to the factored version, and count the gates. Same truth table, one fewer gate. That is the argument for simplifying.
Adders and combinational logic
A full adder is three chips: two XORs from a 74HC86 for the sum, two ANDs from a 74HC08 and one OR from a 74HC32 for the carry. Set A, B and carry-in on slide switches and read the sum and carry on two LEDs. The adder page goes from the half adder to a two-bit ripple-carry adder.
Latches and flip-flops
Two cross-coupled NAND gates from one 74HC00 make an SR latch, the smallest circuit that remembers. The next step is the edge-triggered D flip-flop in a 74HC74, clocked by a button, where moving the D switch alone changes nothing until the clock rises. The flip-flops page has both, plus a JK flip-flop built from a D.
Counters and clocks
Tie a flip-flop’s D input to its own Q-bar and it divides its clock by two. Chain two and you have a counter. Here a 555 supplies the clock and a logic analyzer shows the clock and both bits together, which is where the ripple in “ripple counter” becomes visible. The dedicated counter chips (the 74HC161, the 74HC193 and the CD4017) are in the catalog too, but building the first counter from flip-flops is the better lesson.
The 555 timer
An astable 555 blinks an LED at a rate set by two resistors and a capacitor, and a slide switch changes the rate while it runs. The monostable page covers the other mode: one press, one pulse of a set length, with a calculator and a scope.
Microcontrollers
The course usually ends where logic meets code. An Arduino Uno runs real compiled C++ in the tab, with the same pin numbers as the board on a desk. Start with Blink, then read a switch and drive the same LEDs the logic units used, so students see a program doing the job a handful of gates did.
Assigning it to a class
A routine that works with every circuit here: students predict the outputs on paper first, then open the circuit and test every input combination, then write one sentence on any row where the prediction was wrong and why. The prediction is what makes it a lab rather than a demo, and a wrong row is the most useful thing a student can find.
Every circuit on this page opens and runs without an account. If you want students to save work and submit it, a class on the Teacher plan ($129 a year, up to 40 students) lets you give out a starter, watch progress and collect submissions, and a free 30-day classroom trial runs one class once per account. The printable lesson plan below has the circuit list and a short assessment.
Questions
Is this a Project Lead The Way resource?
No. Mokxi is not affiliated with PLTW, and this page does not use or reproduce PLTW activities. The units are the standard topics of any introductory digital electronics course, and the circuits are ours.
Which parts are missing for a full digital electronics course?
Programmable logic devices and HDL. The chips most courses use are in the catalog: the gates, the 74HC74, the 555, the CD4511 decoder, the 74HC138, the 74HC161 and 74HC193 counters, the CD4017, the seven-segment display and the instruments.
Do students need accounts?
Not to open and run a circuit. They need one to save work or join a class.
Keep going
Build this for real
Open the editor, change a value and watch the number move with it. Nothing to install, and no account needed.