Logic Circuit Simulator Online
A free online simulator where you build digital circuits from logic gates right in your browser — from the first wire to a working 8-bit processor. Nothing to install: open the page and start building.
What you can build in the simulator
The simulator is organized as a course of 47 levels in 4 parts. Each level is a specific circuit you build from available components and verify against a truth table:
- Basic gates. Start with a wire, then build NOT, AND, OR and XOR from the NAND gate.
- Arithmetic. A half adder, full adder and 8-bit adder teach the circuit to add numbers.
- Memory and time. An SR latch, D flip-flop and 8-bit register are the basis of all memory. Add a clock generator.
- Processor. An ALU, program counter and decoder — and by level 16 you assemble an 8-bit computer with assembly.
- Peripherals. A gamepad, matrix display and random generator — and your own processor runs Snake.
- Verilog and FPGA. Levels 30–47 describe circuits in Verilog; the final level exports the project to a ZIP for a real Tang Nano 9K board.
Sandbox: two modes
The sandbox is free experimentation — no checks, no limits. The Sandbox button offers two variants:
Circuit
Build circuits with the mouse from a palette. 32 components are available right away — from logic gates to ROM, RAM, the ALU, a gamepad and a matrix display — plus everything you unlock in the levels. The clock controller and the assembler (once you add a ROM) switch on automatically, and the circuit autosaves.
Verilog
The same experiments, but in code: describe a module in Verilog — the IDE checks syntax, builds an RTL schematic and draws a timing diagram. Instead of a palette you use language primitives: and, or, xor, not, dff.
Ready-made examples in Circuit — loaded with one click from an empty sandbox:
Clock Beacon
A clock generator wired to a display: press ▶ and the value blinks 0 and 1.
Half Adder
Adds two bits: sum and carry. Flip the A and B toggles.
0–255 Counter
A register adds 1 every tick — watch the display.
Random Number Generator
An LFSR produces a new "random" number on every tick.
Running Light
A ROM program drives the program counter: a light runs across the bits.
Ready-made examples in Verilog:
Half Adder
xor + and: sum and carry from two inputs.
Blink (T flip-flop)
dff and not divide the clock by 2: the output blinks 0, 1, 0, 1…
4-bit Counter
A synchronous 0–15 counter: an and/xor carry chain.
MUX 2→1
A multiplexer built from not/and/or: picks a or b by the s signal.
Running Light
An 8-dff Johnson counter: a wave of bits runs one way, then back.
How to start
- Open the simulator. Go to Levels mode — the first level is waiting.
- Build a circuit. Drag components from the palette onto the canvas and connect them with wires.
- Verify and pass. Press Check (F9) — the simulator runs the circuit against the truth table and tells you what to fix.
Stuck? Press the hint button or ask the AI tutor — it analyzes your circuit and asks guiding questions.
Who it is for
The simulator suits school students learning computer science, university students, and anyone curious about how a computer really works — from silicon to code. The course is used as a basis for a school curriculum in circuitry.
Other tools
- Truth table generator — enter a Boolean formula and get the full table.
- Number base converter — convert between binary, decimal and hexadecimal.
- Knowledge library — 46 articles and 43 component datasheets on circuitry.