Circuit design: what it is, why it matters, how to start from scratch
Circuit design is the engineering of logic circuits: how a device is built out of wires, gates and memory elements, and how a computer is built out of devices. This page collects everything a beginner needs: what a circuit is made of, how the field differs from programming, which books to read, what the job looks like, and where to practise — across 47 levels of a browser-based trainer.
What circuit design actually is
In short: it is the engineering of logic circuits. Not "drawing pretty schematics", but solving a problem: a signal arrived, so the circuit must produce the right answer, fit inside the clock, draw little current and not disturb its neighbours.
The field splits into four skills. You train the first three in the early parts of the course, and the fourth becomes the main one in part 2 and in the Verilog part:
| Skill | What it covers | Where you practise it |
|---|---|---|
| Boolean logic | Gates, truth tables, De Morgan's laws, minimisation, Karnaugh maps | Levels 1–5, the article from truth table to circuit |
| Reading and drawing schematics | Component symbols, nets and buses, power, hierarchical blocks | Levels 1–2, the article how to read a schematic diagram |
| Memory and state | Feedback, latches, flip-flops, registers, setup and hold windows | Levels 10–12, the article on windows around a clock |
| Architecture | Adder, ALU, instruction decoder, program and data memory, instruction set | Levels 13–29 and 30–47, the course curriculum |
The third skill is the most underestimated one. Memory and state are what separate a circuit that "computes" from a circuit that "remembers": while there is no feedback in the loop, any function can be reduced to a combination of gates, and adding a single flip-flop turns it into a sequential machine.
What a circuit is made of
Every circuit, from two gates to a full processor, is built from six things. It pays to know them by sight — everything else you assemble out of them for months:
- A signal — one logical value: 0 or 1. In a circuit these are not "weak" and "strong"; they are two states, and physically they correspond to voltage ranges covered separately in the article on TTL and CMOS levels.
- A wire — a connection between one element's output and another's input. A dot at a crossing means the lines are electrically joined; no dot means they merely pass by.
- A gate — an element without memory: AND, OR, NOT, XOR and their inverted forms. The output depends only on the inputs at that moment.
- A flip-flop — an element with one bit of memory: it stores a value and presents it on the next clock edge. Eight flip-flops side by side form an 8-bit register.
- A bus — several signals drawn as one line and labelled with their width:
D[7..0]is eight wires, not a "complicated signal". - A block — a rectangle with a name inside, hiding a whole subcircuit such as an ALU or an instruction decoder. A rectangle with pin numbers on it is a physical chip.
Combinational and sequential logic
All digital design divides neatly into two classes. A combinational circuit remembers nothing: a signal arrives, a gate computes, and forgets. A sequential circuit keeps state between clock cycles, so its output depends not only on the inputs but also on what came before.
The boundary sits wherever the first flip-flop appears. You can redraw the combinational half of a processor from scratch and get the same result; the sequential half you cannot, because carrying state forward is its entire purpose. A dedicated article covers both classes with course examples, including glitches and synchronisation, while the latch walkthrough shows how memory emerges from two gates with feedback.
The learning path
The Ershov Computer trainer is 47 levels in four parts. Every level gives you a task with a truth table, and you assemble a circuit out of components on the canvas; checking happens against the table, not by eye. The full timeline with expected time and outcome is in the course curriculum.
| Part | Levels | What you have to understand and build |
|---|---|---|
| Part 1. Logic | 1–16 | A wire, gates built from one element, an adder, a multiplexer, a latch, a flip-flop, a register, an ALU, a program counter. It starts at level 1, where the whole circuit is one wire |
| Part 2. Architecture | 17–29 | An instruction decoder, Harvard architecture, an assembler, peripherals, and your own game running on your own processor |
| Part 3. Verilog | 30–43 | Describing hardware in text: modules, buses, memory, timing diagrams and debugging in the RTL Viewer |
| Part 4. Your own computer | 44–47 | Designing a complete computer and exporting it as a ZIP for a real Tang Nano 9K board |
The first ten levels take a few evenings, which is a comfortable pace for learning the mechanics without getting stuck. After that the difficulty sets the speed: level 14 on the ALU module and level 18, where the processor is assembled as a whole, require understanding the earlier steps, not just care.
What the course covers and what a university covers
An honest answer: the course does not replace a university programme and does not prepare you for a diploma project. It covers what usually comes first in a degree and normally needs a live electronics lab — and it does it in evenings rather than a semester.
| Topic | In this course | In a university programme |
|---|---|---|
| Boolean logic and gates | Yes: from level 1, checked against a truth table | Yes: usually in one of the first courses, in more depth and with proof exercises |
| Processor-level circuit design | Yes: adder, ALU, registers, memory, decoder, program counter | Yes: the same set, but on real chips and with delay calculations |
| Voltage levels and timing | Explained at the level of meaning: voltages, setup/hold windows, delays | A full course: datasheet calculations, SPICE models, measurements on a bench |
| Hardware description languages | Yes: Verilog in part 3, from one module to a processor | Yes: Verilog and SystemVerilog, plus verification and timing analysis |
| Analogue circuit design | No: the trainer is digital | Yes, as a separate course: amplifiers, filters, power supplies |
| Chip design and fabrication | One introductory topic: FPGA, ASIC or microcontroller | The full route: microarchitecture, synthesis, physical design, verification |
| Lab work and grades | None | Yes: a bench, a lab report, a grade |
The practical conclusion: if you need to understand how a processor works and verify it with your own hands, the course gets you there in evenings. If you need a diploma, lab reports and team work, go to university and use the course as preparation so that your first encounter with the subject is not in a lab report. The boundary between roles is covered in the article on the schematics engineer.
Books worth reading on the subject
The list of circuit design books is long, and what usually wins is not the most complete one but the one you finish. So we do not retell the contents of thick volumes; we work out who each book suits and how to read it alongside the course.
- The Art of Electronics by Horowitz and Hill — the classic for anyone moving past digital logic into the analogue side: editions, chapter order, and the point where a beginner should pause.
- Books on digital logic and circuit design — a curated list with an honest "who is this for" note: the single book for the first year, Harris and Martin, the classics, and the picks for those heading into RTL or FPGAs.
It pays to verify book facts in the publisher's catalogue rather than in online summaries: a typo in the title of a page people will cite costs more than an hour of checking. On reading technical books and datasheets in English, see the project history and the methodology guide.
Who works in this field
Circuit designers build what ends up "inside" every piece of digital hardware: from a microcontroller in a kettle to a processor in a server. They take requirements, break them into registers and blocks, describe the hardware in a description language, and then make sure it meets timing and power budgets.
For the profession itself, salary ballparks, the boundary with RTL engineering and verification, and how to start without a microelectronics degree, see the dedicated article: schematics engineer — the role and how to get there. And the architecture you assemble in the trainer, described in terms of an industry standard, is covered in the article on RISC-V.
Tools
There is no need to compute boolean functions in your head — free online tools exist, and all of them work without installation:
| Tool | What it does | When it helps |
|---|---|---|
| Truth Table Generator | Builds a truth table from a boolean formula | Checking that you understood a gate-level task |
| Boolean Function Calculator | DNF, CNF, Zhegalkin polynomial, minimisation, Karnaugh map | Levels 4–5 and the article on Karnaugh maps |
| Number Base Converter | Converts numbers and two's complement | Part 2 of the course: addresses, data, operands |
| Logic Circuit Simulator | Assembles a circuit with the mouse and checks it against a truth table | Practice with no risk: mistakes show up immediately and no board burns |
| Assembly Simulator | Runs programs for the 8-bit processor step by step, with breakpoints | Once the processor is built and you want to see what it actually does |
| Component datasheets | Truth tables, pinouts and behaviour of the trainer's elements | Settles "but what element is this?" in a minute |
What sets the trainer apart from all of these utilities is that it uses the same components you build the processor from, and the same truth table you are checked against. You can start with a placement test — it shows which level to continue from if you already know your logic.
Common questions about circuit design
What is circuit design?
It is the engineering of logic circuits: how a device is built out of wires, gates and memory elements, and how a computer is built out of devices. The field has four skills: boolean logic, reading and drawing schematics, memory and state, and computer architecture. Everything you do in the browser-based trainer is circuit design at teaching scale: from a single wire at level 1 to a processor described in Verilog.
How is circuit design different from programming?
In programming you describe actions for a machine somebody else has already built. In circuit design you build the machine itself: wires, gates, flip-flops, memory. A mistake in a circuit cannot be fixed by shipping a new version of a file, because the connection has to be redrawn. At level 4 it becomes clear that a circuit is a program written not in instructions but in connections. That is why the developer who wrote the code for a processor and the engineer who assembles that processor are two different entry points into one profession.
Do I need to be able to draw schematics before I start?
No, but knowing the symbols pays off from the first level: the gate on a schematic and the gate in the simulator palette are the same element. A simulator is the easiest place to practise, because the circuit is checked against a truth table immediately and a mistake shows up at the output rather than on a frozen oscilloscope. Once the basics are in place, reading other people's schematics comes on its own: how to read a schematic diagram.
How long does a basic circuit design course take?
The full trainer path is 47 levels in four parts: logic from a wire to a processor, architecture with an assembler, Verilog, and designing a computer for an FPGA board. The first ten levels take a few evenings, and after that the difficulty sets the pace, because every level builds on the one before it. Nobody rushes you: there is no timer, and hints come in a circle — the second and third walk you through a worked solution.