Gates, flip-flops, registers, counters, RAM, ROM, an 8-bit ALU, and full CPU blocks.
Digital Logic LabReleased
Start at one gate. Finish at a CPU.
A digital-logic workbench with sixty-one components and an event-driven timing model. Wire an AND gate first, then continue to an 8-bit processor that executes assembly you wrote yourself.
Runs in your browser · no installation · build without signing in
The actual Logic Lab workspace — palette, canvas, oscilloscope, and displays in one browser bench
Open the Logic LabA dependency-ordered path from digital signals and truth tables to memory and processor control.
Write assembly, load it into ROM, and step the machine through your own program.
Direct answer
What is DigiSim Logic Lab?
DigiSim Logic Lab is an online digital-logic simulator for studying how a computer can be organized from gates, registers, memory, and control logic. You drag components onto a canvas, wire pin to pin, and an event-driven engine evaluates the circuit with per-component modeled propagation delay. Alongside 0 and 1, the lab represents undefined, high-impedance, and contention states so tri-state buses and model-level timing faults remain visible.
Best for: secondary-school logic through undergraduate computer architecture, processor-design coursework, and anyone who wants to see fetch–decode–execute happen instead of reading about it.
SimCastDigital Logic Lab
12 modules · 98 live circuitsGuided Logic course
98 lessons in a structured learning sequence.
Each SimCast builds its circuit in front of you and explains why every component goes where it does. Every lesson is a live bench, so you can stop mid-sentence and probe the thing being described.
The first 22 lessons — from digital signals and binary through Boolean simplification and don’t-care conditions — are public. Pro opens the complete course.
Browse all Logic lessons
Beginner · Logic FundamentalsTwo-Key AND Gate Demonstration
Beginner · Logic FundamentalsBuffer Fan-Out Demonstration
Beginner · Logic FundamentalsThree-Switch OR Gate Lighting Circuit
Beginner · Logic FundamentalsNOT Gate Dual-Output Inverter
Beginner · Logic FundamentalsThree-Sensor OR Gate Alarm Logic
Beginner · Logic Fundamentals2-Input OR Gate- FOUNDATIONSFoundations5
- GATESGates14
- BOOLEAN_ALGEBRABoolean algebra8
- ARITHMETICArithmetic13
- DATA_ROUTINGData routing13
- SEQUENTIALSequential13
- REGISTERS_COUNTERSRegisters and counters11
- MEMORY_SYSTEMSMemory and systems4
- BUSESBuses and transfer2
- ARITHMETIC_UNITThe arithmetic unit3
- PROCESSORThe processor9
- COMPUTERThe computer3
From an empty canvas to a running circuit in four steps
How it worksNothing is hidden behind a form. You place the parts, you make the connections, and the consequence of both is what you read back.
- 01
Open a template or an empty canvas
Start from a finished adder, counter, or ALU and take it apart, or drag your own gates in from the palette. Templates open in the same editor — nothing is read-only.
- 02
Wire output pin to input pin
Drag from one pin to another and the wire routes itself orthogonally. Connected wires are color-coded by state — including high impedance — so you can read the circuit without probing it.
- 03
Drive it and change one thing
Flip a switch, set a clock frequency, or load a program. The event-driven engine schedules the resulting state changes in simulator time without requiring a circuit rebuild.
- 04
Probe it until you know why
Put the scope on the clock and the suspect signal, compare what you expected against what arrived, correct the wiring, then continue with the next section.
Tools for examining a computer from the gate level up
A workbench, not a diagram toolThe Logic Lab pairs its component catalog with instrumentation, so you can build a circuit, observe its simulated states, and investigate why it behaves as it does without leaving the tab.
61 components, one palette
Seven gate types and buffers, switches and constants, multiplexers, encoders, adders, comparators, latches, flip-flops, registers, counters, 256×8 RAM and ROM, program counter, instruction register, and control unit.
Modeled digital timing you can inspect
Connect the eight-channel logic oscilloscope to supported signals and compare transitions in simulator time. It can expose authored propagation delays, ordering effects, and model-level races; it does not measure transistor behavior, analog signal integrity, or timing on physical hardware.
Assembly that runs on your own machine
The Assembly Program Loader assembles source into bytes and transfers them to a wired RAM through address, data, and control pins. Write LDA, ADD, STA, and JMP, complete the load, then step the processor you wired through its fetch–decode–execute cycle.
Output worth looking at
Seven-segment displays turn multi-bit values into readable digits, and a 16×16 pixel screen gives a CPU project something to actually draw on. Counter values and memory contents stop being hex dumps.
Complex systems stay inspectable
Build a register file or an ALU from visible gates and wires, then probe any signal with the oscilloscope as the design runs. The implementation stays open to inspection instead of disappearing behind a custom block.
Portable project files
Circuits save in browser-local storage without an account, and lab-specific undo and redo cover recent edits. A .digi project can be exported as JSON; rendered PNG or SVG export is available only where the active plan and product capability permit it.
Who it is for
For the point where the diagram stops explaining it
Use it where breadboards are impractical, where a class needs to see the same circuit at once, or where a concept only lands once you have broken it yourself.
Architecture lectures
Open a public-access datapath on the projector, break it mid-explanation, and distribute a supported .digi file afterwards. Students need only the access level required by the components used; Classroom availability is a separate institutional question.
Coursework and capstones
Design a processor, document it with supported rendered exports when available, and submit the .digi project file. Its JSON representation can support instructor-developed inspection workflows, but DigiSim does not claim automatic grading from the file alone.
Learning it on your own
Follow the lesson sequence at the pace the material requires, with no kit to buy and no logic analyzer to borrow. Repeat the experiment until the relationship is clear.
The free tier is a real workbench. Pro completes the machine.
Honest accessThere is no trial clock and no watermark. Free includes the core 16-component bench and 22 lessons; Pro adds the memory, CPU, and instrumentation a processor project needs.
Free
Enough to master the foundations
Open the bench without an account and learn digital signals, gates, Boolean logic, and circuit timing with the core parts a first course reaches for.
22 / 98narrated lessons free
- Switches, clocks, constants, buffers, and all seven gates
- Lamps, digit displays, seven-segment displays, and text labels
- An oscilloscope and 22 interactive lessons
- Local autosave and .digi export, no account
ProINCLUDED WITH PRO
Everything needed to build a processor
Add memory, the CPU library, and the assembly loader, then continue from the first truth table to a machine running your own program.
61 / 61components included
- 256×8 RAM and ROM, 8-bit ALU, and CPU blocks
- Assembly loader and 16×16 pixel screen
- Eight-channel oscilloscope
- All 98 lessons and the full template library
Questions
Before you open it
Is it really simulating, or just animating?
Simulating. The engine is event-driven with per-component modeled propagation delay, tri-state and high-impedance pins, and bus-contention detection. The logic oscilloscope displays supported signals in simulator time, including ordering effects and model-level races; it is not a measurement of physical-device timing.
Can I actually program the CPU I build?
Yes. Wire an 8-bit CPU or open one from the template library, write assembly in the Assembly Program Loader, and transfer the assembled bytes into a wired RAM through its address, data, and control pins. You can then observe fetch–decode–execute and, in a suitable circuit, output on the 16×16 pixel screen. The compact instruction set includes LDA, STA, ADD, and JMP.
What exactly is free?
The 16-component core workbench and the first 22 lessons, with no time limit and no account required. Pro adds the memory and CPU components, the assembly loader, the complete instrumentation set, and the remaining lessons.
Where do my circuits live, and can I get them out?
In your browser’s local storage, saved automatically. Export any circuit as a .digi file — plain JSON — or as PNG or SVG. Local storage does not sync between browsers, so export before you switch machines.
Can I use it with a class?
Yes — distribute a starter circuit as a .digi file and collect the completed one back. DigiSim does not provide a general gradebook or automatic grading; Classroom provides Logic Lab assignment results, text feedback, and CSV export. Annual seat subscriptions and administrator invoices are available.
Three more ways in
Relay Lab
Electromechanical control models with 112 governed catalog entries
Relay Lab
Electricity Lab
Modeled DC networks with batteries, meters, and bulbs
Electricity Lab
Analog Lab
Op-amps and filters using Rust/WebAssembly modified nodal analysis
Analog LabThe first gate takes a minute
The processor is the same work, continued. Open a bench and find out how far you get before you need anything from us.
Open the Logic LabFree to start · no account · runs in your browser